connecting rod & rod length too stroke info

grumpyvette · Oct 14, 2008

I build mostly BBC engines, but most of this info also applies to SBC connecting rod selection,
I was asked if stock rods were ok or should they swap to better ARP bolts or BUY the BETTER RODS WITH THE UPGRADED BOLTS,
the first thing Id point out is that, in most cases, when I diagnose engine failures , I see that its usually related to rod bolt stretch or valve train control issues or failures to check clearances, or occasionally failure to provide cooling or lubrication that are the major factors that cause problems, but by far, failure to check clearances, valve train stability issues at higher rpms and rod bolt stretch, and detonation issues are more common.
no connecting rod made can successfully compress bent valves or loose chunks of detonation damaged piston, without damage occurring

https://garage.grumpysperformance.com/index.php?threads/dynamic-static-comp-ratio-cranking-pressure-calculator.4458/page-3

some basic bbc math, to get you thinking about your potential dream bbc combos.

I recently had a discussion with one of the local guys concerning what heads and rotating assembly he should buy now that he recently purchased a tall deck (10.2") big block chevy block. he has a perfectly good 427 forged crank (3.76" stroke) but hes seriously thinking of buying a (4.25" stroke)...

garage.grumpysperformance.com

Compression Ratio Calculator - Wallace Racing

http://www.wiseco.com/Calculators.aspx

http://garage.grumpysperformance.co...-about-your-potential-dream-bbc-combos.14607/

Damper Size for 327

Hi guys I just sent my short block out to get redone. new rods ( scat), pistons .060 over racetec. small journal 327. ARP everywhere. I had a 8in performance damper and the guy doing the work ( one of the best in the area) said the 6in is what he recommends. He will of course rebalance the...

garage.grumpysperformance.com

failure to verify clearances, verify valve train geometry , provide lubrication, and maintain cooling , stay out of DETONATION,or use of inferior components or exceeding your engines valve train control limitations, or red line on rotating assembly design strength can get darn expensive
read these links

notice how the longer crank stroke effects the piston stroke distance in the bore, both at the lower and upper end of the cylinder
http://arp-bolts.com/pages/technical_failures.shtml

http://www.hotrod.com/techarticles/stee ... index.html

http://garage.grumpysperformance.co...calculate-the-bore-stroke-displacement.14906/

link too bore vs stroke info on hundreds of engines
http://users.erols.com/srweiss/tablersn.htm

the 7/16" ARP connecting rod bolts are about 18% larger in cross sectional area than the 3/8" bolts and the better L19 or ARP 2000 bolts are a MINIMUM of 150% stronger than stock bolts even in the smaller 3/8" size,, the larger 7/16" is at least 200% stronger than the stock bolts in the rods., now rods can fail from high rpms and stress in other areas but its the rod bolts that fail in many cases, and in no case would I advise the use of stock 3/8" bolt connecting rods with lots of mileage on them be reused. the (H) design rods can be made slightly lighter in total weight than a similar (I) beam rod, in the common 4340 steel forgings ,but tends to cost slightly more,(notice I DIDN'T SAY I BEAM RODS are STRONGER, but STRONGER FOR A GIVEN WEIGHT) the weak point is usually the connecting rod bolts not the rod forging itself, always go with the 7/16" ARP bolts and the BOLT upgrade is advisable to L19 or better bolts once you start expecting to exceed 4000 feet per minute in piston speed, and its almost mandatory over 600hp and 4500 fpm (FEET PER MINUTE)in piston speed.
strength, obviously it depends on materials, design, care in manufacturing and which connecting rods are being compared properly prepared LS7 or L88 big block rods are a whole lot stronger than the stock 3/8" rod bolts big block rods, but many of the better aftermarket rods are significantly stronger that even the l88 rods
I beam rods typically have a balance pad and thats a good feature, typical H beam rods are SUPPOSED TO BE nearly identical in weight, as they are usually machined not castings (obviously they too occasionally need to be balanced)
theres not a thing wrong with either the (H) or (I) designs if the quality is there in the design and manufacturing.
for most high performance cars,the choice should probably be based on which design has better clearance too the cam lobes and block rails and the use of 7/16" arp bolts, and what kind of package deal you can get on an INTERNALLY BALANCED CRANK, DESIGNED FOR THE RODS if your looking to build the better assembly.
If your build any BBC engine as a general rule, you can expect to see about 1-to-1.3 hp and 1.2-to-1.4 ft lbs of torque per cubic inch of displacement at the flywheel, from a properly designed engine, using higher quality components,
yes you can improve both figures but as power goes up so does component cost.
so basically there's a noticeable boost in power if you build the larger displacement engines, especially if you keep the compression ratio. up or above 9.5:1, max power will require race octane fuel and compression ratios above 12.5:1, and cams with enough lift and duration to make low speed driving in traffic miserable, and these engines will NOT be useful designs for street performance use.

look most stock chevy connecting rods are rated at no more than 6000rpm and 450-500hp
one factor to keep in mind is that rods typically have a side that rides against its matched companion and a side thats BEVELED for clearance on the crank journals radias EXAMPLE

notice how one side of the bearing holding section has a radias (left) but the opposite sides flush (right)

if you wonder why I suggest using SCAT (H) beam style cap screw connecting rods vs stock or most (I) beam designs this picture should show the increased cam to connecting rod clearance
the best solution from a performance perspective is to do the required calculations to select the longest length connecting rod and the lowest weight piston,
of a decent design that will reduce the reciprocating mass significantly more.
the tall deck has a 10.2" deck height, a good dual plane aluminum high rise intake manifold will tend to provide the best compromise if you use a low compression and mild cam duration,
while it might seem like a waste of time, now, reading the links and sub-links will provide a good base to work from, later and save you a great deal of wasted time and money
you have a choice, you can slap the components you own together, now and live with what you have built regardless of the results , or you can put some real thought into making the result perform and carefully select parts and significantly boost power... yes that routes more expensive up front, but in the long term it tends to get better results and cost LESS.
common BB CHEVY piston compression heights are
1.270"
1.395"
1.520"
1.645"
1.765"
remember the blocks deck height, minus the piston pin height minus 1/2 the crank stroke will equal the required connecting rod length
OR
the blocks deck height, minus the connecting rod length, minus 1/2 the crank stroke. will equal the required piston pin height

if you wonder why I suggest using SCAT (H) beam style cap screw connecting rods vs stock or most (I) beam designs this picture should show the increased cam to connecting rod clearance

After market performance ,big block connecting rods come in several common lengths

6.7-6.8"

https://www.summitracing.com/parts/esp-67003dl19/overview/make/chevrolet

https://www.summitracing.com/parts/cpi-u16230/overview/make/chevrolet

https://www.summitracing.com/parts/sca-6670022a/overview/make/chevrolet

https://www.summitracing.com/parts/sca-6680022a/overview/make/chevrolet

https://www.summitracing.com/parts/sca-6680022/overview/make/chevrolet

notice the pin height in the pistons pictured above allow a longer or shorter connecting rod length

heres a selection of commonly available big block chevy connecting rod lengths

https://www.uempistons.com/index.php?main_page=calculators&type=deck

https://www.uempistons.com/index.ph...n_comp&zenid=a0b4d1c0899b781e5a1cffb2fe0afe21

your going to want the longer length and 150%-200% stronger aftermarket connecting rods with the much stronger 7/16" ARP rod bolts if your building a tall deck BBC engine,
so if your trying to build the best combo, you should select the longest and strongest connecting rods that allows you to select an off the shelf compression height piston to save money,
keep in mind head gaskets come in head gaskets come in .010 steps from about .020-to-about .80 and blocks generally measure 10.223 if that O.E.M. block has not previously machined, try too get the quench in the .040-.044 range,
you can get the piston thats compression height is .010-.015, .020 , .025, below or above the deck height, and with a matched head gasket get the quench correct after measuring the deck height, and compression height.

Diamond_12711_nitrousdome__25621.1432240797.png

I recently helped one of the local guys assemble a 496 BBC 4.25" stroke
engine using 6.385: SCAT rods with 12.7:1 pistons thats being built
I watched him start to install the first piston with the dome facing the lifter gallery, or upper side of the cylinder... I waited until he had started to install the connecting rod cap on that first rod and asked him to rotate the crank to TDC I handed him a bridge and a dial indicator

https://www.uempistons.com/index.php?main_page=calculators&type=deck

https://www.uempistons.com/index.ph...n_comp&zenid=a0b4d1c0899b781e5a1cffb2fe0afe21

and asked him to verify the deck height.....honestly I had a real hard time not laughing.....I think most of us realize that we all made similar mistakes.... no harm done (YET).
after a few seconds, I suggested he check the spark plug clearance with the head just laid on the block with an old head gasket...yeah, he caught the mistake then!

heres a selection of commonly available big block chevy connecting rod lengths
now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.
cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is approx .15 sq inches BTW when you go to buy a ring compressor....this type works far better than the others

http://store.summitracing.com/partdetail.asp?autofilter=1&part=PRO-66766&N=700+115&autoview=sku

http://garage.grumpysperformance.co...g-and-installing-connecting-rods-pistons.247/

Proform 66766 $31

common sbc pin height info
Specs

Comp Height 5.565" Rod - 1.561
Comp Height 5.7" Rod - 1.433
Comp Height 6.0" Rod - 1.13
Pin Diameter - 0.9272

how they work is you clamp it around your piston and adjust it to that size before the rings are installed so the piston is a snug slide thru fit, then, install the rings, dip the rings and piston in clean oil, place the compressor over the cylinder on the block with the base firmly held against the block deck and push the piston into its much larger open entrance, as it slides thru the funnel like construction squeezes the rings into the grooves and they can,t spring back until they are in the bore, remember to line up the rod bolts and having them covered with the ends of a 3 ft long section or 3/8" fuel line to protect the crank journal is a good idea, having a ROD GUIDE TOOL you can use to guide and PULL THE PISTON INTO THE BORE WITH IS EVEN A BETTER IDEA
use those good L19 bolts and assuming you sellected the good L19 bolts that test at 220,000 psi, for each the differance is 24.2 thousand lbs vs 33 thousand lbs or a 36% increase in strength, but the stock rod bolts are 160,000 psi so your really swapping from about 17.6 thousand to 33 thousand in strength or an 88% stronger rod bolt

http://arp-bolts.com/pages/technical_torque_us.shtml

http://arp-bolts.com/pages/technical_installation.shtml

redline

youll generally find that 4000 FPM (FEET PER MINUTE)of piston speed with stock parts or 4500fpm with VERY good quality forged parts is the reasonable limit on the lower end ROTATING ASSEMBLY stress, if you don,t think selecting high quality components and correctly assembling them is...

garage.grumpysperformance.com

http://issuu.com/arpbolts/docs/catalog2 ... ipBtn=true

reasonable quality connecting rods are CHEAP

http://www.cnc-motorsports.com/product.asp?ProdID=3150

http://www.cnc-motorsports.com/product.asp?ProdID=8817

keep in mind if a rod comes loose at high rpms you'll be LUCKY to save the intake, heads, blocks and cam are frequently damaged, spending an extra $90 for the better rod bolts is a total no brainer, in my opinion, if spending an extra $400-500 on rods and $90 on better bolts prevents rod failures, thats a minor consideration, when you may be spending $5500-$12,000 plus on an engine build.
you might also want to be aware that over revving and floating the valves, and using a poorly designed oil system is a major potential source of engine failures
I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... and keep in mind a good deal of what might appear to be rod/rod bolt failures, are ACTUALLY the result of over revving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods

well worth reading

http://www.rehermorrison.com/techtalk/63.htm

http://arp-bolts.com/pages/technical_failures.shtml

IM OFTEN ASKED WHY I DON,T REBUILD CHEVY CONNECTING RODS, WELL MAYBE A PICTURE WILL HELP,

a good set of SCAT FORGED 4340 forged connecting rods costs less than $400 and they are 150%-200% stronger than MOST OEM chevy SBC rods
it will cost you almost that much to replace the bolts with ARP wave lock bolts, balance and polish and resize stock rods and you have far weaker rods when your done

Do not assume all the rod bolts will all take the same torque to get to the specified listed stretch

SUMMIT SELLS ROD BOLT STRETCH GAUGES
http://www.summitracing.com/parts/ARP-100-9942/

grumpyvette · Oct 27, 2008

Re: connecting rod info

http://victorylibrary.com/mopar/rod-tech-c.htm

http://www.stahlheaders.com/Lit_Rod Length.htm

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

http://rustpuppy.org/rodstudy.htm

http://www.iskycams.com/techtips.php#2005

http://drag.race-cars.com/techtips/tech ... 1047440910

http://www.grapeaperacing.com/GrapeApeR ... ngrods.pdf

http://www.hotrod.com/techarticles/stee ... index.html

Aftermarket Connecting Rod Manufacturers
Rod Manufacturer Tech Support # Website
Argo +61 (02) 4934 7099 (Australia) argorace.com.au
Arrow Precision +44 (0) 1455 234200 arrowprecision.com
Bill Miller +1 (775) 887-1299 bmeltd.com
Brian Crower +1 (619) 749-9018 briancrower.com
CAT +1 (626) 330-1999 catpep.com
Callies +1 (419) 435-2711 callies.com
Crower +1 (619) 661-6477 crower.com
Dyers +1 (815) 657-9970 dyersrods.com
Eagle +1 (662) 796-7373 eaglerod.com
EARP Machine +1 (928) 428-3835
GRP +1 (303) 935-7565 grpconrods.com
Howards Cams +1 (920) 233-5228 howardscams.com
K1 Technologies +1 (440) 497-3100 k1technologies.com
Lunati +1 (662) 892-1500 lunatipower.com
Manley +1 (732) 905-3366 manleyperformance.com
Molnar Technologies +1 (616) 940-4640
Ohio Crankshaft +1 (937) 548-7113 ohiocrank.com
Oliver +1 (616) 451-8333 oliver-rods.com
Pauter Machine +1 (619) 422-5384 pauter.com
RPM +1 (562) 926-9188 rpmmachine.com
R&R Machine +1 (941) 621-8143 rrconnectingrods.com
Saenz +1 (305) 717-3422 saenzgroup.net
Scat +1 (310) 370-5501 scatcrankshafts.com
Swanson +1 (574) 858-9406 spmtitaniumrods.com
Wagler Competition Products +1 (812) 636-0391 email Wagler
Wossner +1 (865) 862-5264 wossneronline.com
ZRP Europe +30 2108251640 zrp-rods.com

displacement = bore x bore x stroke x 8 x .7854

1/2 stroke + rod length+piston pin compression height,
should roughly equal block deck height ,

Connecting Rods

Connecting Rods sold by SCAT Crankshafts, the leader in high-performance engine components for over 50 years.

www.scatcrankshafts.com

BBC Rods | 396 427 454 502 | Molnar Big Block Chevy Rods

Molnar BBC rods. Big selection of H beam big block Chevy connecting rods. Standard, stroker, turbo, power adder, power adder plus and small journal.

molnarrods.com

9.8 Short deck
Aftermarket block

Bore. Stroke. Rod. Displacement
4.5. 4. 6.385/6.535. 509
4.5. 4.25. 6.135/6.535 540
4.5. 4.5. 6.135. 572
4.56. 4.25. 6.385 555
4.6. 4.25. 6.385. 565

Tall deck 10.2
4.5. 4.25. 6.535. 540
4.5. 4.5. 6.535. 572
4.5. 4.75. 6.7. 604
4.56. 4.25. 6.535. 555
4.6. 4.5. 6.535. 598
plus or minus a few thousandths,
minor adjustments in compression,
due to head gasket thickness and what the piston deck height is are common
common BB CHEVY piston compression heights are
1.270"
1.395"
1.520"
1.645"
1.765"
remember the blocks deck height, minus the piston pin height minus 1/2 the crank stroke will equal the required connecting rod length
OR
the blocks deck height, minus the connecting rod length, minus 1/2 the crank stroke. will equal the required piston pin height
more good info, BTW if your going to buy aftermarket connecting rods a stroker crank, higher compression pistons ETC,
BUY A COMPLETE BALANCED ROTATING ASSEMBLY FROM A SINGLE SOURCE

http://www.adperformance.com/index.php? ... x&cPath=71

http://www.ohiocrank.com/rotatepage1.html

http://www.dougherbert.com/enginecompon ... 1_611.html

when you go to clearance a block and select components read the fine print on what your buying and remember to clearance the block and rods to clear the cam lobes, a clearance of,0.050" is OK, Ive always suggested 0.060" but thats not enough difference in clearance in that application to worry about.
EXAMPLE SCAT,IF your looking to save money theres a good deal of variation in kit components,aftermarket connecting rods with ARP 3/8" bolts are significantly stronger than stock rod bolts, and connecting rods so they are a big improvement, but in the future Id suggest looking at similar 7/16" cap screw rod kits with internally balanced cranks for most builds as the cost is usually only minimally higher.
forged cranks are nice, to brag about, but certainly more expensive and not required for a street/strip 383 that seldom sees 6400rpm,or similar applications
as a general rule you'll find 7/16" rods add about 20% more strength for a minimal cost upgrade.

3/8" rods(Fastener Yield Strength (psi) 160,000 psi)
http://www.summitracing.com/parts/ESP-5700BPLW/

7/16" rods
Fastener Yield Strength (psi)200,000 psi

http://www.summitracing.com/parts/SCA-26000716/

http://www.summitracing.com/parts/SCA-25700716/

grumpyvette · Nov 2, 2008

Re: connecting rod info

I get asked all the time,
"should you re-use those stock rods, when I rebuild my 350 or when I build my 383 stroker"
most sbc gen I stock rods are designed to be cheap,
and dependable in engines spinning under 6000rpm that make under 400hp,
this is one area where ,
I'm simply amused and a bit worried at the lack of thought shown in selecting components, by some guys.
most stock chevy small block rods are VASTLY inferior in strength to many of the mid range and better aftermarket rods available.
a 7/16" cap screw type ARP rod bolt is EASILY 200%-300% stronger than a stock 3/8" factory rod bolt and frankly, the cost & TIME to correctly modify and prep stock rods is a total waste, its almost always cheaper to buy decent aftermarket rods.
Three’s Company: Understanding Rod Length, Piston Compression Height and Crankshaft Stroke

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SPONSORED BY
Diamond Pistons

The relationship between connecting rod length, piston compression height and compression ratio is often misunderstood, largely due to the misuse of the term “compression”. In all honesty it probably shouldn’t be applied to piston terminology at all except as it relates to the shape of the piston crown surface. Compression is a volume related term that refers to compression ratio. It bears no relationship the mechanical link created by a specific crankshaft stroke and connecting rod center-to-center length or the pin position that brings the piston crown essentially even with the top of the bore.

Compression Height (compression distance) is the dimension from the flat top of the piston crown (not inclusive of dome or dish) to the centerline of the piston pin.

This should always be referred to as the pin height to avoid confusion.

We often say an engine has some specified compression ratio, such as 10:1 compression for example. But it is not an appropriate usage when referring to the mechanical interaction of crank stroke and rod length. Pin height is the preferred term and you can see the relationship in the accompanying illustration. With a fixed stroke length, changing the rod length affects two things, neither of which is the compression ratio. It dictates the required pin height to bring the piston crown flush with the block deck at TDC. It also influences the approach and departure speed of the piston relative to TDC and to some degree the piston’s dwell time at TDC.

If you study the accompanying diagram you will note there are four core dimensions governing the crank, rod, piston relationship
Key Engine Dimensions

Block deck height
Stroke length
Rod center to center length
Pin height

The crank throw, connecting rod and piston must all fit within the block height dimension so that the piston deck comes nearly flush with the deck surface at TDC. Because the crank throw rotates about its own center at the main bearing you can see that only half the stroke length is used when the piston is at TDC. The rest of the distance is taken up by the rod length and the pin height of the piston. So, the reciprocating assembly final dimension is calculated as:

½ stroke length + rod length + pin height

Since block height is fixed within a narrow window available for deck milling, the combination of stroke length, rod length and pin height must add up to the same height with a small tolerance for desired deck height and piston to head clearance which also incorporates gasket thickness. A common practice in performance circles is to zero-deck the block. That means that the combination of one half the stroke length plus rod length and pin height equals the fixed deck height of the block. The flat portion of the piston top is exactly even with the deck surface of the block. This forces the builder to select the appropriate compressed gasket thickness to control piston to head clearance. Not surprisingly, most performance head gaskets are .039″ – to .042″ thick when compressed. The commonly accepted minimum piston to head clearance with steel connecting rods is .035″.

Longer rods invariably drive the pin position higher in the piston where it intersects the oil ring groove. Piston manufacturers like Diamond offer an easy solution with an oil ring support rail. Support rails do an excellent job and allow for very short piston heights.
The stroke length is almost always chosen first as it relates to the bore and stroke combination for the desired displacement. Rod length is usually specified next based on the application. Theory on this is widely debated and often contradicting, but as a rule, shorter rods are usually chosen to gain a more rapid departure from TDC as the piston starts down the bore. This opens a larger cylinder filling space more quickly so that a high velocity intake system can start filling the cylinder faster. It is often used to enhance throttle response on applications that are frequently throttled.

Pistons with shorter rods arrive at TDC more briskly and don’t hang around long before they depart swiftly. The piston achieves maximum velocity sooner and at less crank angle, which reduces cylinder volume exposure at the point of maximum pressure differential. Appropriate intake valve timing is required to ensure optimum efficiency under these conditions. Since the piston achieves maximum velocity sooner, the intake valve can be opened sooner to take advantage of the cylinder pressure differential. Less overall cylinder volume is exposed at this point, but the early initiation of flow will chase the piston down the bore as volume exposure rapidly increases. This is commonly referred to as the piston tugging harder on the charge due to its increased acceleration.

This block dimension from the centerline of the main bore dictates the final stack length for the crank, rod, and piston assembly. That includes the rod length, one half the stroke length and the pin height. Rod length and pin height can be juggled according to the application, but the final dimension is always fixed by the block height.
Many racing engines use longer connecting rods to help reduce piston weight while having positive effects on torque curve shape and positioning and combustion efficiency. Longer rods typically require shorter, lighter pistons. This pushes the ring pack higher on the piston. In normally aspirated applications, builders appreciate this because they like to move the ring pack up to lighten the reciprocating assembly, improve piston stability and minimize unburned gasses in the crevice volume above the top ring. However, longer rods in a supercharged application can be problematic because boosted applications need to move the ring pack down the piston to move it farther from excessive heat. Longer rods make this difficult to accomplish as the pin bore intersects the oil ring groove. In many cases a shorter rod can be specified for boosted applications because boost pressure reduces the need for the critical rod/stroke tuning relationships required for efficient normally aspirated operation.

In effect, connecting rods provide an additional tuning component in a competition engine. As rod length (center to center) varies, it affects piston motion such that it can be used as a tuning tool. By influencing piston acceleration and velocity it dictates the rate at which a differential is created between atmospheric pressure (above the carburetor) and cylinder pressure during the intake stroke. Accordingly, it impacts major contributors to the VE equation, i.e. intake and exhaust path cross sections, valve event timing and optimum ignition point.

While these pistons look almost identical, the one on the left is designed for a longer rod (or stroke). This is evident due to the shorter compression height, IE the wrist pin is machined closer to the crown.
Faster exposure to atmospheric pressure improves cylinder filling and thus VE provided intake tract dimensions and valve event timing are appropriately sized and synchronized. It is important to recognize that piston acceleration and velocity are both zero at TDC and BDC. At all points in between, acceleration and velocity are dictated by rod length. For any given rod length, the piston achieves maximum velocity at a precise point in the stroke relative to the crank angle where the rod axis is 90° to the crank throw (typically about 70-75° of crank angle). This point represents the highest rate of pressure drop exposure in the cylinder and is closely tied to intake valve timing for optimum cylinder filling.

Note how the length of the rod alters its angle during the same crankshaft position.
Once rod length is chosen, you have two parts of the equation. Since the rod length and stroke are now fixed, the pin height is the remaining variable. To find the necessary pin height, add the rod length and half of the stroke and subtract the result from the block deck height. Blocks that have not been decked typically provide a fudge factor of about .020″. This is often removed when the block is zero decked to match the piston crown. At this point, the builder can evaluate the available room for the ring pack and determine whether a longer rod negatively impacts ring location.

Note that none of this affects compression ratio. The piston crown still stops at the block deck surface, thus the combustion space (volume) above it remains unaffected unless you alter the head gasket thick- ness. The compression ratio can only be altered by increasing or decreasing the volume of the combustion space above the piston at TDC. And, because the relationships are mechanically fixed, dynamic compression ratio can only be affected by cam timing.

Longer rods can improve rod stroke ratio, reducing thrust loading on the piston. A popular misconception is that rod length affects displacement, which it does not. Only cylinder bore and crankshaft stroke alter the displacement of an engine.
You can use an online calculator (such as that at www.diamondracing.net) to juggle all these figures and determine the best combination for your application. When ordering pistons, your tech rep can also assist you in homing in on the best combination. The tech can also help you with ring pack placement to avoid issues with the valve reliefs. There are multiple ways to package these components depending on the requirements of your application and the tech guys will keep you within the necessary limits to protect your investment.

This article was sponsored by Diamond Pistons. For more information, please visit our website at www.diamondracing.net
related info
http://garage.grumpysperformance.com/index.php?threads/another-496bbc.5123/

http://garage.grumpysperformance.com/index.php?threads/496ci-revamped.14642/

http://garage.grumpysperformance.co...n-wrist-pins-one-really-over-looked-part.978/

http://garage.grumpysperformance.co...g-and-installing-connecting-rods-pistons.247/

http://garage.grumpysperformance.co...-about-your-potential-dream-bbc-combos.14607/

http://garage.grumpysperformance.co...-articles-you-might-want-too-look-over.14682/

http://garage.grumpysperformance.co...ng-and-basic-piston-ring-info-youll-need.509/

http://garage.grumpysperformance.com/index.php?threads/rotating-assembly-bearings.9527/

http://garage.grumpysperformance.com/index.php?threads/maximizing-piston-to-bore-ring-seal.3897/

http://garage.grumpysperformance.com/index.php?threads/big-block-chevy-info.710/#post-72463

http://garage.grumpysperformance.co...in-height-compression-height.5064/#post-66240

http://garage.grumpysperformance.com/index.php?threads/scat-cranks-related-info.10930/

http://garage.grumpysperformance.com/index.php?threads/tall-deck-options.14678/

example

http://www.sdparts.com/product/12495071/5700quotPMConnectingRods.aspx
$265 for a set of stock rods and then you should still have ARP bolts installed, polish, balance and sized your looking at easily $500-$600 or more for a set ready to run

compared to something like this below its a joke

http://store.summitracing.com/partdetail.asp?part=SCA-6570021&autoview=sku

http://store.summitracing.com/partdetail.asp?part=SCA-25700716&autoview=sku

keep in mind theres far stronger rods available if you have some extra cash, and that connecting rods and their rod bolts are under a huge amount of stress at high rpms....one rod bolt stretching at high rpm will usually result in engine failure and its common for only the intake, valve covers, distributor, and water pump and a few other parts to be salvageable if that were to happen at high rpms...stretch a rod bolt and the piston contacts the head, or bends a valve, the rod bends, the heads destroyed, the block can be history and it can go down hill rapidly from there as fragments work their way around thru other of the moving parts as the engine locks up
ITS not generally HP but RPMS or lack of lubrication to the bearings that kills rods, I know guys with turbo cars that have carefully reworked stock rods pushing over 700 hp but they don,t generally exceed 6300rpm, rods generally fail in TENSION when the rod or rod bolts stretch /stretches not in compression due to cylinder pressure.
thats why the 7/16" rod bolts are so much better, as the bolts are the weakest component in most designs
on the compression stroke the whole rod structure resists deformation on the exhaust stroke the rod bolts are playing crack the whip and the rods trying to keep the piston from pulling/distorting it maybe 25-40 thousands it takes to prevent head to piston contact, and the bearing shells from distorting ,under the load so they don,t loose the oil pressure support, if the rod elongates and hits the head or valves in valve float bad things cascade into worse things fast.
the rod bolt cross sectional area is generally far smaller than the rod itself and if the piston compresses the rod a few thousands on the power stroke there not much effected, but let the rod stretch and bad things happen real fast.
a 7/16" rod bolt is about 20% larger in cross section than a 3/8" rod bolt and the L19 ARP steel in the better rod bolts is easily 50%-100% stronger than the stock rod bolt steel in many cases, giving a decent aftermarket cap screw rod design a significant strength advantage

grumpyvette · Nov 3, 2008

Re: connecting rod info

connecting rods and rod bolts are under high stress, levels, if your going to buy cheaper non-brand name rods your taking a greater chance on having a part not meet minimal specs and strength levels than the better brand rods and ARP rod bolts, but that does not mean the rods are necessarily bad or not a good deal.
I've used several OFF brand rods, in builds but I INSIST the guys supplying the parts for those builds use 4340 steel rods with 7/16" ARP rod bolts
READ THIS INFO BELOW

http://www.dragzine.com/tech-storie...campaign=stroker-engines-the-long-and-short-o
We have all heard the adage “there’s no replacement for displacement.” The more air an engine can displace, the more fuel it can burn. Anytime you can add more fuel, more power is sure to follow. This is the reason that turbos and nitrous oxide are so popular. Both force more oxygen into the combustion chamber, allowing additional fuel to be burned. The same concept holds true for displacement.

There are three ways to increase the displacement of an engine: increase the number of cylinders, increase the bore size of the cylinders, or increase the stroke of the crankshaft. The first choice requires a completely different engine block to achieve, so for this article, that narrows the choice down to bore and stroke. Increasing bore size is easy, and is the most common practice. However, an increase in bore size is typically restricted to less than one-hundred-thousandths of an inch (0.100)due to cylinder wall thickness on a stock block. Aftermarket blocks or the installation of cylinder sleeves does allow for more of a size increase, but again that requires a different block or major machine work.

An engine’s stroke on the other hand, can typically be increased by five-hundred-thousandths (1/2-inch) or more in some stock blocks. The result is a large increase in cubic-inch displacement. Using an aftermarket block could allow for even more of an increase, and of course, there are always limitations and other things to consider. An engine builder must consider all factors when designing a stroker engine for a particular application. Chapters could be written covering all of those factors, but for this article, the focus will be kept on the physical (dimensional) and dynamic (operational) properties associated with selecting connecting rod length for a stroker engine. We spoke with Tom Lieb of Scat Enterprises, Trip Manley of Manley Performance, and Kirk Peters of Lunati so we could get their take on the effect of engine performance in regards to connecting rod length. It should be noted that these concepts are based on differing rod lengths using the same stroke (comparing a 5.7-inch rod to a 6.0-inch rod in a 383 ci Chevy stroker) not necessarily rod length in general (comparing rod length in a 383 ci small-block to rod length in a 632 ci big-block) unless otherwise noted.

Rotating Assembly Height

When you increase the stroke of a crankshaft, each journal will rotate on a larger diameter. Think ofcrankshaft stroke as a circle. The centers of the crankshaft’s main journals represent the center of the circle. The centers of the connecting rod journals represent the outside of the circle. As the crankshaft rotates (circular motion) the rod journal travels in a circle, which has a diameter equal to the stroke.

When a given cylinder is at top dead center (TDC), the rod journal is directly above zero degrees of rotation on the center of the circle. At bottom dead center (BDC), it is 180 degrees directly below the center. Although the big end of the connecting rod (connected to the crankshaft) travels in a circular motion, the small end (connected to the piston) travels in a reciprocating motion (up and down). The connecting rod converts the rotation of the crankshaft into a reciprocating motion of the piston. The total movement of the piston from TDC to BDC is equal to stroke.
pi
Rotating assembly height is equal to half of the stroke, plus the connecting rod length, plus the compression height of the piston. The goal is to achieve a rotating assembly height that will provide the desired deck volume or clearance for a particular application. Deck volume or clearance is determined by finding the difference between rotating assembly height and the deck height. Deck height is measured from the center of the main journal bores to the top of the block’s deck. An engine where rotating assembly height and deck height are equal is considered a zero-deck engine.

There may be multiple combinations of connecting rod length and piston compression height available for a particular stroker engine. A long rod will require a short compression height piston (distance from the center of the wrist pin to the top of the piston crown), and a short rod will require a tall compression height to achieve the same assembly height. Before selecting which combination of rod and piston you will use, there are a few factors to consider.

Engine Balance

Once the desired assembly height has been determined, rod length and piston compression height are selected. A short rod will require a taller compression height piston than a long rod would require and vise-versa. The weight of the components should be considered. A piston with more compression height will also weigh more than a piston with less compression height for the same application. A heavier piston requires the crankshaft to have heavier counter weights to offset the additional reciprocating weight of the piston. This may even require additional weight to be added externally to the harmonic balancer and flywheel. When this is the case, the engine is considered to be externally balanced.

Any additional weight incurred by using a longer connecting rod has less of an effect on counter balance weight because the connecting rod is both reciprocating and rotating. Reciprocating weight requires more weight to offset than rotating weight. The difference in connecting rod weight is split between rotational and reciprocating while differences in piston weight is only applied to reciprocating weight. Using a lighter piston will allow for lighter crankshaft counterweights and may not require any additional weight to be added externally. When this is the case, the rotating assembly is considered to be internally balanced.

Lieb, says that many times, the connecting rod length is determined by whether or not the engine builder is looking for an internally or externally-balanced engine.

pi2
Piston Design and Stability

While on the topic of piston compression height, it is worthy to note that more compression height will allow for more room between the top of the piston crown and ring pack. Manley states, “Performance engines today are all about power adders. For the tuner crowd it’s boost, and for the drag racer, it’s big-blocks on nitrous. With a short rod, the piston pin is moved lower on the piston, creating a better ring pack for boost.” In addition, more compression height can increase the thickness of material on the deck of the piston, which provides increased strength for higher cylinder pressures created by power adders.
Stability of the piston should also be considered. A longer connecting rod will keep the piston further up in the cylinder bore when at BDC than a short rod would in the same application. Keep in mind, this comparison is true, only if we are using the same piston and only changing connecting rod length. If a different piston is used, the location of the wrist pin in relation to compression height could be different, thereby changing piston location at BDC.

This is important if the piston skirt comes out of the bore. The further the piston skirt moves out of the bore, the more piston rock becomes an issue. Piston rock ultimately causes a loss of ring seal. The piston skirt contacting the cylinder wall is what limits the rocking motion of the piston.

Rod Angle

As the crankshaft rotates the big end of the connecting rod, the small end is moving up and down. This creates an angle between the cylinder wall and the connecting rod. The severity of the angle is determined by the ratio of rod length to stroke (rod ratio). Rod ratio is determined by dividing the rod length by the stroke.

Common Formulas For Building Stroker Engines

A few formulas you need to know when building a stroker engine:

Displacement in cubic inches = Bore x Bore x Stroke x Number of Cylinders x .7854
Assembly Height = (Stroke / 2) + Rod Length + Piston compression height
Rod Ratio = Rod Length / Stroke
Mean Piston Speed (feet per second) = (2 x Stroke x RPM / 60) / 12

A shorter rod will decrease rod ratio, while a longer rod will increase the ratio for the same stroke. As the ratio decreases, the rod angularity, or angle between the connecting rod and cylinder wall, will increase. The maximum achieved angle always occurs at 90 degrees before and after TDC. Increasing rod angularity (decreased rod ratio) increases the amount of thrust acting on the cylinder wall, and the result is increased frictional loss and wear on the piston skirt and cylinder wall in some cases.

All three rod manufacturers that we consulted had a slightly different view when it came to rod ratio.

According to Lieb, “Any angle that does not exceed 20, 21, 22 degrees is a non-event. When you look at a 410 ci Chevy sprint car engine with a 6-inch rod, that angle is pretty severe, and those engines run pretty good.”

A 410 ci small-block’s rod ratio when using a 6-inch rod, will be in the 1.5 to 1.6 ratio range, depending on the bore and stroke combination used to achieve 410 cubic-inches. The maximum rod angle for a 1.5 rod ratio is just under 19.5 degrees, and that falls into Lieb’s non-event category. He adds, “When you get into big-block stuff where you have a 4.750-inch stroke, then you get into some issues.”

Manley pointed out the large range of ratios from 1.87 in the Nissan GTR engine to less than 1.5 in some big-block strokers. “Rod ratio is not as important as other factors,” stated Manley, referring to moving ring location down with a short rod for boosted engines.

Peters suggests using, “As high a ratio as possible,” citing less rod angularity, reduced reciprocating weight due to a shorter compression height piston (remember, although a long rod will weigh more, the difference is not as significant because it is split between rotating and reciprocating mass), and reduced piston rock as benefits.

Rod length and ratio further affect one of the most important aspects of a stroker engine’s performance — piston speed.

Piston Speed

It is common to see formulas and calculators that will determine mean piston speed. This is simply the average speed of the piston for the given stroke at a set RPM. Mean piston speed will always be the same for the given stroke, regardless of connecting rod length. Peak piston speed, on the other hand, is dependent on rod length.

[A change in performance] has nothing to do with rod length, per se, it has to do with the relationship of the piston when the valves open or close. – Tom Lieb, Scat Enterprises, Inc.

Piston speed is zero at TDC and increases as it accelerates toward BDC. The speed peaks at a specific degree after TDC (ATDC), and then decelerates back to zero at BDC. The piston accelerates on its way back toward TDC reaching its maximum speed at the same specific degree before TDC (BTDC). The peak piston speed (at a given RPM) is determined by the actual rod length and stroke, while the degree of rotation at which it occurs is determined by the rod ratio.

A common error that is made regarding peak piston speed is assuming that it occurs at 90 degrees of rotation — which is not true. Peak speed actually occurs somewhere around 70 to 75 degrees BTDC and ATDC (depending on rod ratio) due to the angle of the rod affecting piston speed and location. Peak piston speed is higher with a short rod compared to a long rod (stroke being the same), because the shorter rod creates a greater angle.

As mentioned previously, the rod ratio determines at what degree in rotation peak speed occurs. As rod ratio decreases (shorter rod), the number of degrees before and after TDC at which peak speed occurs also decreases (in other words, peak speed occurs closer to TDC). This also means the piston starts to decelerate sooner in rotation with a shorter rod. Therefore, piston speed is less with a short rod on the lower half of the stroke (across BDC) than (refer to the graph provided by Prestige Motorsports).

The significance of a rod length’s effect on piston speed is ultimately dependent on piston speed in relationship to valve events. “The rod length and stroke of the crankshaft determines piston speed,” Lieb says. “[A change in performance] has nothing to do with rod length, per se, it has to do with the relationship of the piston when the valves open or close.”

In today’s engine building, one would use a shorter rod when the engine builder wants to improve the scavenging effect at lower RPM. – Kirk Peters, Lunati

This applies to both piston position and speed. The greatest difference in piston position will occur at the largest rod angle, or 90 degrees before and after TDC. A short rod will put the top of the piston further down the bore at this point as compared to a long rod on the same stroke (due to the angle of the short rod being greater). The difference in position has the largest effect on exhaust valve opening and intake valve closing. The opening of the intake and closing of the exhaust occur near TDC where piston position only differs by a few thousandths-of-an-inch or less (because the difference in rod angle between a short and long rod at this point in rotation is minimal).

“In today’s engine building, one would use a shorter rod when the engine builder wants to improve the scavenging effect at lower RPM,” Peters stated.

This is true because piston speed has a greater effect than piston position during overlap. Piston speed is near its peak when overlap begins before TDC. A short rod will carry more speed from the peak back to TDC, and again back toward the peak (in other words, there are less degrees of rotation between peaks). Therefore, rod length can significantly affect the scavenge effect due its affect on piston speed. A short rod will increase piston speed during overlap allowing the benefit of scavenging to occur at a lower RPM than a long rod.
The camshaft’s intake lobe opening ramp also follows right along with piston acceleration. A short rod will provide more piston speed on the opening side, but lower speeds on the closing side. The exhaust lobe, on the other hand, is opening and closing on the BDC side of rotation where a short rod provides slower piston speeds. Therefore, a long rod will increase piston speed during the exhaust events.

Conclusion

Stroker engines provide a significant increase in displacement. While an increase in displacement alone will provide for additional power, there are many factors to consider to get the most out of the increased stroke. Connecting rod length is one aspect to consider when designing a stroker engine.

Rod length changes both the physical and dynamic properties of the engine. Factors such as assembly height, engine balance, piston ring location, and cylinder length are physical features that must be considered, while rod angle and piston speed are dynamic characteristics affected by rod length. The dynamic characteristics will change engine performance based on their relationship to camshaft events.

As an engine builder, it is important to take all aspects into consideration, and understand how one component will affect the overall combination. Rod length alone cannot be generalized as providing a certain change to every engine. Rather, any change in engine performance is due to the rod length’s role in changing the dynamic properties of the entire combination.

THINK THROUGH YOUR OPTIONS AND THE COMPLETE COMBO,
I see guys have long discussions about things like the difference in port cross sectional area or the best connecting rod length, to use, no one factor is going to make your engine totally dominate the competition, its a combo of small almost insignificant individual component choices being made and a good deal of time and effort taken during the assembly and clearancing work, that stack up to give you or prevent you from maximizing the engines performance.
you may not even think about factors like polishing crank journals, or valve train geometry or intake runner cross sectioinal area or length ,or intake runner port matching or surface finish, but the combined effects of your choices and components selected do mater!
look guys I think a good deal of this discussion is missing the point here, Ive built well over 150 engines in the last 45 years, (I lost cound decades ago)
but I can assure you that longer rods and the easily verifyable slight increase in dwell time, the longer rods produce will be totally meaningless UNLESS, you design the engine for and select components too take full advantage of the minor increase, by carefully calculating the REQUIRED compression ratio,fuel octane required,all the factors related to the cam timing,(duration,lift, LCA) you calculate and build and install, and tune the engine for , a matched exhaust header scavenging (header primairy length and diameter plus collector design) and the intake runner length and cross sectional area, to maximize the cylinder scavenging effects, plus you match the fuel/air ratio, and ignition advance curve, to maximize that longer dwell times potential advantage.

RELATED INFO
http://garage.grumpysperformance.com/index.php?threads/types-of-crankshaft-steel.204/

http://garage.grumpysperformance.com/index.php?threads/connecting-rod-strength-h-vs-i-beam.1168/
SCAT , EAGLE and CAT parts have all proven to function
heres some sources I use

http://www.scatenterprises.com/

http://www.survivalmotorsports.com/

http://www.adperformance.com/

http://www.dougherbert.com/

grumpyvette · Nov 13, 2008

Re: connecting rod info

don,t get too concerned about your choice, between connecting rod lengths, here Ive built enought engines with both rod lengths to be sure both can result in a good combos

http://www.cnc-motorsports.com/product.asp?ProdID=8089

http://www.cnc-motorsports.com/product.asp?ProdID=8087

http://www.cnc-motorsports.com/product.asp?ProdID=3145&CtgID=1003

http://www.cnc-motorsports.com/product.asp?ProdID=6922&CtgID=1003

PROS/cons for 6"

KEEP IN MIND!!
the crank you select must have counter weights and clearances matching the rods you select, an INTERNALLY BALANCED CRANK IS UNDER LESS HIGH RPM STRESS
NEXT the ROD BOLTS you use in EITHER rod should be the ARP 7/16" CAP SCREW DESIGN as they are at least 150% -200% stronger than the stock 3/8" rod bolt and nut designs, and its the rod bolts stretching that cause many problems, BALANCING THE FULL ASSEMBLY IS CRITICAL TO LONG LIFE

Longer rod ratios have a longer dwell at TDC ,
In theory thats more high rpm tq for the 6" rods due to more efficient use of cylinder pressure at those high rpms but cam timing, scavenging and compression ratio must match to get the benefits, and detonation could be slightly more common
MATCHED ,CAM TIMING, PORT CROSS SECTION AND LENGTH< <COMPRESSION< AND EXHAUST HEADER CONSTRUCTION, DESIGNED TO MATCH THE LONGER ROD DWELL TIME IS REQUIRED TO ACCESS THE POTENTIAL BENEFITS, FAIL TO DO THAT CORRECTLY AND YOU LOOSE THE SLIGHT POTENTIAL GAINS
a 5.7" will have longer DWELL at BDC and move away from TDC slightly faster so in theory it can produce better low rpm tq and higher port vacuum readings but again,but cam timing, scavenging and compression ratio must match to get the benefits

less cylinder side wear/loading
lower angle reduces side thrust, and ring wear but the differance is something like two degrees of angle so its not super critical

lower over all piston/rod weight
longer rod allows a shorter piston that weights less and has more counter weight to skirt clearance between piston and crank, generally this makes for slightly less high rpm stress

HIGH PISTON PIN
the 6" rod places the upper edge of the piston pin hole in the lower oil ring, this is generally not a huge problem but more a P.I.T.A. due to extra precausions need to prevent the lower oil scraper from placing the ring gap in the unsupported areas

LOWER PISTON PIN
longer piston skirt, more stable piston in the bore and lower oil ring fully supported, but heavier piston and less clearance on crank counter weights

BOTTOM LINE
ITs generally a toss up as to which is better in a street application, I prefer the 6" but you will have fewer assembly problems with the 5.7" rods

HERES WHAT ISKY CAMS SAYS

"Rod Lengths/Ratios: Much ado about almost nothing.

Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".

To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!

Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).

To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.

In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!

Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.

Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype.

5.70" Verses 6.00" Rod Length Comparison Chart

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

MORE INFO, and yes its worth your time to read thru it

http://www.stahlheaders.com/Lit_Rod Length.htm

http://victorylibrary.com/mopar/rod-tech-c.htm

http://em-ntserver.unl.edu/Mechanics-Pages/Luke-schreier/unzip/Tension and Compression in Connecting Rods VI.htm

http://www.grapeaperacing.com/tech/connectingrods.pdf

grumpyvette · Nov 25, 2008

Re: connecting rod info

I build mostly BBC engines but this also applies to SBC connecting rod sellection, I was asked if stock rods were ok or should they swap to better ARP bolts or BUY the BETTER RODS WITH THE UPGRADED BOLTS

look most stock chevy connecting rods are rated at no more than 6000rpm and 450-500hp

now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.
cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is aprox .15 sq inchs
use those good L19 bolts and assuming you sellected the good L19 bolts that test at 220,000 psi, the differance is 24.2 thousand lbs vs 33 thousand lbs or a 36% increase in strength

http://arp-bolts.com/pages/technical_torque_us.shtml

reasonable quality connecting rods are CHEAP

http://www.cnc-motorsports.com/product.asp?ProdID=3150

http://www.cnc-motorsports.com/product.asp?ProdID=8817

keep in mind if a rod comes loose at high rpms youll be LUCKY to save the intake, heads, blocks and cam are frequently damaged, spending an extra $90 for the better rod bolts is a total no brainer, in my opinion, if spending an extra $400-500 on rods and $90 on better bolts prevents rod failures, thats a minor consideration, when you may be spending $5500-$12,000 plus on an engine build.
you might also want to be aware that over reving and floating the valves, and useing a poorly designed oil system is a major potential source of engine failures

I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... and keep in mind a good deal of what might appear to be rod/rodbolt failures, are ACTUALLY the result of over reving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods

read thru this

http://arp-bolts.com/pages/technical_failures.shtml

How A Stroker Crankshaft Affects Piston Speed and Inertia.

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SPONSORED BY
Wiseco

An intense look at mean piston speed, inertia, and controlling the massive, destructive forces at work inside your engine.

Engine builders have long calculated the mean piston speed of their engines to help identify a possible power loss and risky RPM limits. This math exercise has been especially important when increasing total displacement with a stroker crankshaft, because the mean piston speed will increase when compared to the standard stroke running at the same RPM.

But what if there was another engine dynamic that could give builders a better insight into the durability of the reciprocating assembly?

“Rather than focus on mean piston speed, look at the effect of inertia force on the piston,” suggests Dave Fussner, head of research and development at Wiseco Pistons.

Let’s first review the definition of mean piston speed, also called the average piston speed. It’s the effective distance a piston travels in a given unit of time, and it’s usually expressed in feet per minute (fpm) for comparison purposes. The standard mathematical equation is rather basic:

Mean Piston Speed (fpm)=(Stroke x 2 x RPM)/12

There’s a simpler formula, but more on the math later. A piston’s velocity constantly changes as it moves from top dead center (TDC) to bottom dead center (BDC) and back to TDC during one revolution of the crankshaft. At TDC and BDC, the speed is 0 fpm, and at some point during both the downstroke and upstroke it will accelerate to a maximum velocity before decelerating and returning to 0 fpm.

As the piston races from bottom dead center to top dead center, for a brief moment, it comes to a complete stop. This places tremendous stress on the wrist pins. Shown, these Trend pins are offered in various wall thicknesses depending on the application.

002wiseco-piston-speed-k1-stroker-crankshaft-300x200.jpg

The mean piston speed takes the total distance the piston travels during one complete crankshaft revolution and multiplies that by the engine RPM. Piston speed obviously increases as the RPM increase, and piston speed also increases as the stroke increases. Let’s look at a quick example.

A big-block Chevy with a 4.000-inch-stroke crankshaft running at 6,500 rpm has mean piston speed of 4,333 fpm. Let’s review the formula again used to calculate this result. Multiply the stroke times 2 and then multiply that figure by the RPM. That will give you the total number inches the piston traveled in one minute. In this case, the formula is 4 (stroke) x 2 x 6,500 (RPM), which equals 52,000 inches. To read this in feet per minute, divide by 12. Here’s the complete formula:

(4 x 2 x 6,500)/12=4,333 fpm

You can simplify the formula with a little math trick. Divide the numerator and denominator in this equation by 2, and you’ll get the same answer. In other words, multiply the stroke by the RPM, then divide by 6.

(4 x 6,500)/6=4,333 fpm

With this simpler formula, we’ll calculate the mean piston speed with the stroke increased to 4.500 inch.

(4.5 x 6,500)/6=4,875 fpm

As you can see, the mean piston speed increased nearly 13 percent even though the RPM didn’t change.

Reducing piston weight plays a huge role in creating a rotating assembly that can sustain high rpm. The seemingly insignificant gram weight of a piston is magnified exponentially with rpm.
Again, this is the average speed of the piston over the entire stroke. To calculate the maximum speed a piston reaches during the stroke requires a bit more calculus as well as the connecting rod length and the rod angularity respective to crankshaft position. There are online calculators that will compute the exact piston speed at any given crankshaft rotation, but here’s a basic formula that engine builders have often used that doesn’t require rod length:

Maximum Piston Speed (fpm)=((Stroke x ?)/12)x RPM

Let’s calculate the maximum piston speed for our stroker BBC:

((4.5 x 3.1416)/12)x 6,500=7,658 fpm

By converting feet per minute to miles per hour (1 fpm = 0.011364 mph), this piston goes from 0 to 87 mph in about two inches, then and back to zero within the remaining space of a 4.5-inch deep cylinder. Now consider that a BBC piston weighs about 1.3 pounds, and you can get an idea of the tremendous forces placed on the crankshaft, connecting rod and wrist pin—which is why Fussner suggests looking at the inertia force.

“Inertia is the property of matter that causes it to resist any change in its motion,” explains Fussner. “This principle of physics is especially important in the design of pistons for high-performance applications.”

When the connecting rod is lengthened, it provides a softer transition as the piston changes direction. The longer connecting rod also reduces the compression height of the piston and can help pull weight out of the rotating assembly.
The force of inertia is a function of mass times acceleration, and the magnitude of these forces increases as the square of the engine speed. In other words, if you double the engine speed from 3,000 to 6,000 rpm, the forces acting on the piston don’t double—they quadruple.

“Once started on its way up the cylinder, the piston with its related components attempt to keep going,” reminds Fussner. “Its motion is arrested and immediately reversed only by the action of the connecting rod and the momentum of the crankshaft.”

Due to rod angularity—which is affected by connecting rod length and engine stroke—the piston doesn’t reach its maximum upward or downward velocity until
about 76 degrees before and after TDC with the exact positions depending on the rod-length-to-stroke ratio,” says Fussner.

Stroker cranks such as this forged LS7 piece from K1 Technologies, are a great way to add displacement. However, when the stroke is lengthened the piston must accelerate faster each revolution to cover the larger swept area of the cylinder wall.
“This means the piston has about 152 degrees of crank rotation to get from maximum speed down to zero and back to maximum speed during the upper half of the stroke. And then about 208 degrees to go through the same sequence during the lower half of the stroke. The upward inertia force is therefore greater than the downward inertia force.”

If you don’t consider the connecting rod, there’s a formula for calculating the primary inertia force:

0.0000142 x Piston Weight (lb) x RPM2 x Stroke (in) = Inertia Force

The piston weight includes the rings, pin and retainers. Let’s look at a simple example of a single-cylinder engine with a 3.000-inch stroke (same as a 283ci and 302ci Chevy small-block) and a 1.000-pound (453.5 grams) piston assembly running at 6,000 rpm:

0.0000142 x 1 x 6,000 x 6,000 x 3 = 1,534 lbs

With some additional math using the rod length and stroke, a correction factor can be obtained to improve the accuracy of the inertia force results.

Crank Radius÷Rod Lenth

“Because of the effect of the connecting rod, the force required to stop and restart the piston is at maximum at TDC,” says Fussner. “The effect of the connecting rod is to increase the primary force at TDC and decrease the primary force at BDC by this R/L factor.”

For this example, the radius is half the crankshaft stroke (1.5 inch) divided by a rod length of 6.000 inches for a factor of .25 or 383 pounds (1,534 x 0.25 = 383). This factor is added to the original inertia force for the upward stroke and subtracted on the downward movement.

Both the crank on the left and right are at the same point in their respective rotations. However, the piston on the left will have to travel much faster to reach top dead center at the same time as the piston on the right.
“So, the actual upward force at TDC becomes 1,917 pounds and the actual downward force at BDC becomes 1,151 pounds,” says Fussner. “These forces vary in direct proportion to the weight of the piston assembly and the stroke to rod length and they also vary in proportion to the square of the engine speed. Therefore, these figures can be taken as basic ones for easily estimating the forces generated in any other size engine.”

As the piston reaches top dead center on the exhaust stroke, there is no cushion of compression to help slow it down. Instead, the connecting rod takes the full brunt of the force which pulls on its beam and tries to separate its cap. Quality connecting rods are paramount to a high-horsepower, high-rpm engine.
“We know a common measure used for many years to suggest the structural integrity danger zone of a piston in a running engine is mean piston speed,” sums up Fussner. “As the skydive instructor told his student, it’s not the speed of the fall that hurts, it’s the sudden stop. And so it is with pistons. So rather than focus only on the mean piston speed, let’s decide to also consider the effect of inertia force on the piston, and what we can do to reduce that force. And if that is not possible, make sure the components are strong enough to endure the task we have set forth.”

This article was sponsored by Wiseco. For more information, please visit our website at wiseco.com

grumpyvette · Nov 26, 2008

Re: connecting rod info

no one ever said this hobby is cheap! think how foolish youll feel if a rod fails simply because you got cheap and tried to save $50-$100 at the cost of allowing your rods to be %50 weaker than spending $50-$100 more on your combo could have done.
lets look at it...
the first thing I do with 3/8" bolt big block rods is sell them,you can usually get ($50-$70 a set for them)
heres why
the 7/16" ARP connecting rod bolts are about 18% larger in cross sectional area than the 3/8" bolts and the better L19 or ARP 2000 bolts are a MINIMUM of 150% stronger than stock bolts even in the smaller 3/8" size,, the larger 7/16" is at least 200% stronger than the stock bolts in the rods.
but ID strongly resist the urge to just drill out and install 7/16" ARP rod bolts in rods designed for the 3/8" rod bolts, theres a very good chance youll have removed enought material from around the bolt to effect its strength.
the amazing thing is that the total out the door cost of even the moderate aftermarket forged 4340 cap screw rods, is similar or even cheaper than the ,machine shop cost of the arp bolts and reworking the stock connecting rods.
BTW THE $90 ROD BOLT UPGRADE IS WELL WORTH IT IF YOUR PUSHING THE UPPER RPM LIMITS IN YOUR ENGINE BUILD

http://www.adperformance.com/index.php? ... cts_id=519

http://www.adperformance.com/index.php? ... cts_id=243

your average machine shop charges at least $120 to add the bolts and resize the rods, the bolts themselfs cost about $80, so your into those rods for about $200 minimum,now if your smart youll also have them magnaflux checked for stress cracks (another $50 minimum)now that $$200-$250 machine shop cost plus the $50-$70 minimum youll normally make selling the stock rods goes a LONG WAY toward upgradeing) yet a 3/8" rod bolt is a MINIMUM of 7000psi weaker than a 7/16 rod bolt due to the differance in cross section, now add to that the fact that the (H) style rods are rated at LEAST 50% stronger,are usually lighter in weight and closer in tollerance and require less ballancing and youll quickly find that the work necessary to get those 3/8" rods up to racing condition is wasted time and money in a true high performance engine

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1397&prmenbr=361

lets see, recondition old 3/8" rods = hours of work and costs $250-$300 minimum and they are still 50% weaker
OR
buy new (H) style cap screw 7/16" rods that are 50% stronger that require HOURS less work, are closer tollerance and cost on average $350-$400 NEW [color:"black"]remember that $400 is really minus the $250-$300 youll spend on the old rods so its only $50-$100 more for the up-grade [/color] plus they have more cam to rod bolt clearance in the block and require less grinding on the pan rails if a stroker cranks used, and if your buying pistons also you can buy a longer rod at minimal cost to improve the engines rod/stroke ratio!

http://www.flatlanderracing.com/crhbeamscat.htmlIF you already have 3/8" bolt big block rods and are about to rebuild the big block engine, please understand IM CERTAINLY NOT trying to rain on your parade! what I am trying to do is show anyone reading the thread, that the stock 3/8" rods are not the best choice to spend your money on and that proper planing helps the over all combos strength for the money spent
IVE seen to many guys spend major amounts of money
pollishing
shot peaning
resizing
ballancing
and ,magnafluxing stock rods
and winding up spending more and having less with stock rods then they might have had for the same or less money with aftermarket FORGED 7/16" bolt rods with careful shopping. you will occasionally get great deals on those rods on EBAY or at the LOCAL speed shops

grumpyvette · Dec 20, 2008

Re: connecting rod info

GOSFAST posted this great photo to illustrate the differance between rod designs

http://www.scatcrankshafts.com/index.htm
paint, marker etc. tends to wash off, you really should lightly die stamp the main caps

https://www.harborfreight.com/36-pi...mping-set-63675.html?_br_psugg_q=number+stamp

rods designed like the 3 SERIES generally won,t work with stroker cranks while the 2 series usually will

the connecting rods you sellect make a huge differance in the rod to cam lobe clearance, even a small base cam won,t clear some designs, it should be obvious that the connecting rod with the thru bolt has a great deal less cam lobe clearance potentially than the cap screw design next to it., and the cap screw rod probably clears the blocks oil pan rail area easier also

Im running that crane 119661 cam retarded 4 degrees BTW but detonation has not been a problem, remember that the coolant temp, air temps the engine sees, QUENCH distance, type of head gasket and its construction ,ignition advance,plug heat range,piston to bore clearance, exhaust valve seat width, and oil temp and pollishing your combustion chamber and piston domes, and your AIR/FUEL RATIO , and the effective DYNAMIC compression ratio, have a noticable effect on detonation

and if you do see detonation, theres octane boosters like TOULUENE

if you wonder why I suggest using SCAT (H) beam style cap screw connecting rods vs stock or most (I) beam designs this picture should show the increased cam to connecting rod clearance

notice the pin height in the pistons pictured above allow a longer or shorter connecting rod length

heres a selection of commonly available big block chevy connecting rod lengths
now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.
cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is approx .15 sq inches BTW when you go to buy a ring compressor....this type works far better than the others

http://www.gnttype.org/techarea/misc/octanebooster.html

http://www.team.net/sol/tech/octane_b.html

http://www.elektro.com/~audi/audi/toluene.html

READ THIS

http://www.rehermorrison.com/techtalk/02.htm

many guys don,t realize that the rod bolt material and cross sectional area are critical to durrability , especially in a high rpm range combo,while the rods themselfs ocassionally fail, its much more likely that the rod bolts lost thier clamping strength, stretched a bit first and that was a major contributing factor in the bearing failure or the rod failure process.

interesting info from ARP

Other Stresses

It must be realized that the direct reciprocating load is not the only source of stresses in bolts. A secondary effect arises because of the flexibility of the journal end of the connecting rod. The reciprocating load causes bending deformation of the bolted joint (yes, even steel deforms under load). This deformation causes bending stresses in the bolt as well as in the rod itself. These bending stresses fluctuate from zero to their maximum level during each revolution of the crankshaft.

Fastener Load

The first step in the process of designing a connecting rod bolt is to determine the load that it must carry. This is accomplished by calculating the dynamic force caused by the oscillating piston and connecting rod. This force is determined from the classical concept that force equals mass times acceleration. The mass includes the mass of the piston plus a portion of the mass of the rod. This mass undergoes oscillating motion as the crankshaft rotates. The resulting acceleration, which is at its maximum value when the piston is at top dead center and bottom dead center, is proportional to the stroke and the square of the engine speed. The oscillating force is sometimes called the reciprocating weight. Its numerical value is proportional to:
It is seen that the design load, the reciprocating weight, depends on the square of the RPM speed. This means that if the speed is doubled, for example, the design load is increased by a factor of 4. This relationship is shown graphically below for one particular rod and piston

http://www.arp-bolts.com/Tech/TechWhy.html

I did a quick DOUBLE TAKE on that bottom graph the first time also....look closer at the edges of the graph, its points out the STRONGER the material USED the SMALLER the dia. necessary for a given tensile strength, your limited in clearance on rod bolt max size so the material needs to have higher yeild strength, and potential durrability, to increase the rod bolt strength

FROM ARP

"Metallurgy for the Non-Engineer

By Russell Sherman, PE

1. What is grain size and how important is it?

Metals freeze from the liquid state during melting from many origins (called allotropic) and each one of these origins grows until it bumps into another during freezing. Each of these is a grain and in castings, they are fairly large. Grains can be refined (made smaller); therefore, many more of them can occupy the same space, by first cold working and then by recrystallizing at high temperature. Alloy steels, like chrome moly, do not need any cold work; to do this â€“ reheat treatment will refine the grain size. But austenitic steels and aluminum require cold work first. Grain size is very important for mechanical properties. High temperature creep properties are enhanced by large grains but good toughness and fatigue require fine grain size-the finer the better. (High temp creep occurs at elevated temperature and depending on material and load could be as much as .001 per inch/per hour.) All ARP bolts and studs are fine grain â€“ usually ASTM 8 or finer. With 10 being the finest.

2. How do you get toughness vs. brittleness?

With steels, as the strength goes up, the toughness decreases. At too high a strength, the metal tends to be brittle. And threads accentuate the brittleness. A tool steel which can be heat-treated to 350,000 psi, would be a disaster as a bolt because of the threads."

http://www.arp-bolts.com/Tech/TechMetals.html

grumpyvette · Dec 24, 2008

Re: connecting rod info

theres a wide sellection of connecting rods you can choose from,and even some of the less expensive 4340 steel rods with ARP 7/16" rod bolts make a decent component for a street strip engine up to easily 600hp, , but its very hard to tell just looking, because the type of steel,critical measurements, heat treating and pollishing are hard to identify by looks,alone,IVE used alot of SCAT,AND CROWER rods and a few LUNATI and MANLEY and all the 4340 STEEL RODS with 7/16" ARP bolts have worked just fine.
I would strongly suggest a KNOWN NAME brand and insist on ARP bolts
NEVER SCRIMP ON RODS, ROD BOLTS, BEARINGS OR VALVE SPRINGS
more connecting rod info

http://www.nolimitmotorsport.com/eagle/

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

grumpyvette · Dec 31, 2008

Re: connecting rod info

http://store.summitracing.com/partdetai ... toview=sku

http://store.summitracing.com/partdetai ... toview=sku

heres a stretch chart
http://www.arp-bolts.com/Tech/TechTorque.html

Do not assume all the rod bolts will all take the same torque to get to the specified listed stretch

SUMMIT SELLS ROD BOLT STRETCH GAUGES
http://www.summitracing.com/parts/ARP-100-9942/

heres the short version,AFTER each rods installed with its bearing on the crank, durring the short block assembly process,set the stretch gauge to zero on the bolts unstretched length, you use a torque wrench on rod bolts lubed with assembly lube too tighten each of them in several stages, tighten the rod bolts to the recomended torque then loosen them and re-tighten them a minimum of three times each, after the final torque value is reached for the third time, you check each bolt against the chart values, most will be a bit short,of the full permited stretch value, while the bolts being meassured , you can slip the stretch gauge off for a second and use the correct long wrench to further tighten them slowly and carefully too just under or up too the stretch chart limits in length, if they are not at that length due to the torque wrench stretching the bolt,this insures max clamping loads, without exceeding the bolts elastic limits so its at max holding strength for the application. cycling the bolt thru several cycles tends to make sure its firmly seated and fully stretched and tends to find problems like deffective bolts, and bolt that doesn,t shrink back below the chart value when the tensions released is deffective and needs replacement

FROM ARP

"We highly recommend using a stretch gauge when installing rod bolts and other fasteners where it is possible to measure the length of the fastener. It is the most accurate way to determine the correct pre-load in the rod bolt.

Simply follow manufacturerâ€™s instructions, or use the chart on page 25 of the ARP catalog for ARP fasteners.

Measure the fastener prior to starting, and monitor overall length during installation. When the bolt has stretched the specified amount, the correct preload, or clamping load, has been applied.

We recommend you maintain a chart of all rod bolts, and copy down the length of the fastener prior to and after installation. If there is a permanent increase of .001Ë in length, or if there is deformation, the bolt should be replaced. "

http://www.carcraft.com/techarticles/11 ... index.html

a few more less expensive tools

http://www.chevyhiperformance.com/techa ... rices.html

grumpyvette · Nov 13, 2010

bore to stroke ratio

in the constant quest for increased performance many guys install stroker cranks to gain displacement, many guys don,t consider the changes in stroke mandate other changes such as increased friction from the changed rod angles and clearance issues plus the reduction in peak rpms that the increased piston speeds the longer strokes mandate will require.
longer strokes tend to have increased rotational friction and lower rod length to stroke ratios
both tend to limit upper rpm cylinder filling efficiency, longer strokes are not necessarily, a bad thing as the increased displacement helps torque but your valve size needs to keep pace with the displacement, and in many cases the restriction in max valve size, and the related curtain or flow potential, that the engines bore limits you too, will cause major increases in stroke to only produce slightly more torque
the IDEAL bore to stroke ratio and rod length, (from seeing the results of many engine dynos) seem to fall close to a range of stroke should be between about .70-.75 of bore diam.and rod length should be between about 1.55-1.9 times the stroke, but theres been many successful combos that did not fall into that basic range
examples of very efficient engines that maximize the horsepower per cubic inch of their displacement
are the 302 Chevy with its 3" stroke and 4" bore and the 477 BIG BLOCK with its 4.5" bore and 3.76" stroke
neither is ideal but both engine combos tend to produce excellent power for their displacement when the correct components are used to build them, but Id also point out that the common strokes on the same bore (the 383 in the 302s case and the 540bbc in the 477s case)produce MORE TORQUE AND HORSEPOWER, just not as much horse power PER CUBIC INCH OF DISPLACEMENT
in an ideal world having a 1.9:1 rod/stroke is great, in theory its worth a few extra hp and reduces friction and thrust drag on the cylinder walls, in the real world as long as your crank counter weights clear the piston skirts at bdc by at least .060 and the pistons don,t get closer than about .037 to the heads at TDC the rod length is not super critical as long as the piston speed stays under about 4000 fpm (feet per minute)with components similar to stock and with forged balanced components 4500fpm may be tolerated for brief periods...youll seldom have problems unless the valve train or lube system fails

QUOTE
"Under-square engines

These produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke. But, under-square can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft and a smaller bore means smaller valves which restricts gaseous exchange; however, modern technology has lessened these problems (explanation?). An under-square engine usually has a lower redline, but should generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. Going undersquare can cause pistons to wear more quickly (greater side-loads on the cylinder walls) and can cause ring seal problems and lubrication problems; with increased loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings (due to piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss. A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.

Over-square engines

These are generally more reliable, wears less, and can be run at a higher speed. In over-square engines power does not suffer, but low-end torque does - it being relative to crank throw (distance from the crank center to the crank-pin). An over-square engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the over-square engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Breathing is an important advantage for over-square engines, as the edges of the valves are less obstructed by the cylinder wall (called "un-shrouded"). The big bore can fit larger (or more) valves into the head and give them more breathing room.

With shorter crankshaft stroke (and therefore piston travel) parasitic losses are reduced. Ring drag is the major source of internal friction and the crankshaft assembly also rotates in a smaller arc, so the windage is reduced. Oil-pressure problems caused by windage and oil aeration are lessened."

you might want to read thru these links

http://www.strokerengine.com/RodStroke.html

http://www.wallaceracing.com/enginetheory.htm

viewtopic.php?f=53&t=343&p=6341&hilit=redline#p6341

http://www.purplesagetradingpost.com/su ... ngine.html

viewtopic.php?f=53&t=510

http://www.rbracing-rsr.com/runnertorquecalc.html

http://hemrickperformance.com/valve.aspx

http://www.rustpuppy.org/rodstudy.htm

http://www.wallaceracing.com/runnertorquecalc.php

http://www.swartzracingmanifolds.com/tech/index.htm

http://tomorrowstechnician.com/Article/ ... adder.aspx

http://victorylibrary.com/mopar/intake-tech-c.htm

viewtopic.php?f=53&t=343&p=6341&hilit=redline#p6341

http://victorylibrary.com/mopar/chamber-tech-c.htm

http://victorylibrary.com/mopar/cam-tech-c.htm

http://victorylibrary.com/mopar/rod-tech-c.htm

http://victorylibrary.com/mopar/piston_position-c.htm

Bbc Related & Links And Useful Info

a few useful links, and sub links videos, and tips to look over yeah, increased displacement helps and building a killer BBC old school, for your car can be both cost effective and produce impressive results some of the most effective, cost per hp and efficient combo's , will be the 496...

garage.grumpysperformance.com

grumpyvette · Dec 3, 2010

Re: connecting rod info

Connecting Rods - Enginology
On The Rod Again...
From the November, 2010 issue of Circle Track
By Jim McFarland

http://www.circletrack.com/enginetech/c ... ength.html

Connecting Rods
Connecting rod geometry, particularly...

read full caption
Connecting Rods
Connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions.
It is generally acknowledged that connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions. These include specific relationships to valve timing (camshaft design), cylinder pressure history, spark ignition timing requirements and torque output, the latter with respect to the actual shape of torque curves. We'll touch on the more important of these a bit later.

Depending upon specific applications, connecting rods are perhaps some of the most highly stressed parts in an engine, particularly those intended for racing. From the high loads experienced at and just beyond TDC piston position during combustion to the tensile and unsymmetrical loading caused by offset piston pin axis, loads that are actually opposite to combustion pressure loads and stresses set up by lateral inertia, connecting rods become virtual "whips" that mechanically join pistons to the crankshaft.

Further complicating the issue are vibratory loads caused by oscillatory motion of a crankshaft, rotating about its axis while spinning in a normal direction. Visualize this set of load conditions in very slow motion. Each firing impulse intended to accelerate crankshaft rotation is applied as a force delivered in a span of time. Because of its inertia, a crankshaft can't immediately increase its speed and, therefore, is momentarily deflected in the same direction as its rotation. This deflection is local to the crank pin to which the load-delivering connecting rod is attached. Then, because of its elasticity, the crankshaft (at that pin location) will spring back against its direction of rotation, continuing this back-and-forth oscillatory motion until the next firing pulse is delivered to that particular crank pin. The connecting rod is thereby required to absorb what amounts to a series of tensile and compressive loads caused by oscillations of the crank pin, during primary crankshaft rotation.

Keep in mind that we've just provided a very simplistic description of the load dynamics experienced by the connecting rod for only one operational cylinder. The complexity of this varying load environment is increased by orders of magnitude when you add another seven cylinders and turn up the wick on rpm. So, when you think about connecting rods as "shock absorbers," several issues come to mind.

For example, consider cylinder pressure loads not as "hammer blows" to a piston but very rapid pressure rises that are influenced by combustion flame rate and net combustion pressure development. We also know that this pressure "history" is not constant or uniform as it is applied to a piston. Plus, whatever auxiliary forces are applied to a piston are also transferred in some way into the connecting rod. Rods can be designed too stiff, thereby transferring combustion pressure too aggressively to rod bearings and crank journal bearings. They can also be too flexible, and neither condition is acceptable. But in any case, rods need to absorb load spikes and minimize pressure transfer loss to prevent a waste of torque that's ultimately produced by the crank.

Perhaps one area of concern where connecting rod stiffness is important deals with vibratory loads produced by the torsional stiffness of a connecting rod's beam section, as piston weight is reduced. As you might expect, the reduction of rotating and reciprocating mass in an engine's crankshaft assembly can become a trade-off to the absorption of gas and mechanical loads by sheer mass alone. Visualize throwing a medicine ball to a 150-pound person and then to a 250-pounder and you may understand this more clearly.

Of course, to minimize the rotational resistance of a crankshaft assembly, reducing the weight of pistons and rods is a time-honored approach. However, compromising weight for strength and durability is the fulcrum about which this issue pivots. Perhaps one exception to this "rule" was in the early design of composite connecting rods (the so-called "poly motor" of years past), in which first-design rods were inordinately stiff and caused rod bearing failures for a lack of load absorption capability. On the other hand, lightweight materials that offer strength and low mass may be too costly to market, even in the average racing engine. So while other considerations must be included, the fundamental objectives should include strength, low weight, and durability.

In speaking with leading connecting rod manufacturers, you often hear that a high percentage of rod failures don't occur during the high pressure of combustion. Rather, it's during the exhaust stroke that a rod gets "yanked" away from TDC. This sudden movement of the piston causes abnormally high tensile loads in the rod's beam and leads to a fracture in this area, typically somewhere just below the piston pin end.

Also, failures can occur during either valve float or conditions of over-revving the engine. What happens is that the open valves (and lost combustion pressure) don't provide any sort of a cushion for pistons heading toward TDC. So when they pass through TDC, there's nothing to stop them from being "pitched" at the cylinder heads, often leading to another cause of tensile fracture in the beam section. In fact, the "effective" or dynamic weight of a piston passing through TDC under these conditions can be far in excess of its actual static weight. Multiple times, in fact.

Connecting Rods - Enginology

Connecting Rods
Connecting rods become virtual...

read full caption
Connecting Rods
Connecting rods become virtual "whips" that mechanically join pistons to the crankshaft and sometimes they fail. But situations like the one pictured above can be avoided by properly selecting and integrating various internal engine components.
Yet another common location for rod failure is a portion sometimes called the "hinge point," which is generally where a connecting rod's beam section changes in cross-section area (wide to narrow). Connecting rod designers frequently work in this area to determine the best compromises between rod strength and material selection. Of course, you should always include proper rod side-clearance, making certain not to provide excessive dimension that allows oil to create over-oiling of cylinder walls. Insufficient side-clearance can lead to over-heated and failed rod bearings, as well.

Finally, if we assume that a piston represents the "floor" of an engine's combustion space, then the rate of piston movement and time spent at each crankshaft angle will affect the rate of change in combustion space (volume). Of the reasons this is important, one is that piston movement can affect mixture density during the compression stroke (and subsequent flame rate and rise of combustion pressure). This, in turn, bears influence on spark ignition timing and the optimization of IMEP (minimizing "negative" torque). During an exhaust cycle, piston motion can also affect efficient cylinder evacuation and, therefore, is linked to proper exhaust valve timing.

Just considering these two peripherals of piston movement, we can immediately see that any changes to a piston's rate of travel may affect net cylinder pressure and power. Connecting rod length can, and does, influence cylinder pressure. Perhaps obscure is the fact that while longer connecting rods produce a larger included angle between rod axis and crank throw (stroke) at the same piston position and crank angle, it is piston motion approaching and leaving TDC and BDC that provides some interesting study.

Here's an example of that. As connecting rod length is increased, piston motion (both acceleration and velocity) away from TDC decreases. This results in a slower rate of pressure drop across the inlet path, therefore causing a reduction in intake flow rate (all else being equal). Unless compensation is made for this change in piston speed, some degree of volumetric efficiency may be lost.

In contrast to this effect upon volumetric efficiency (potential torque), piston "residence time" at and near TDC during combustion tends to hasten flame rate, correspondingly raise cylinder pressure per unit time, and enhance the tendency toward detonation. Reduced initial (or total) ignition spark timing, applied to reduce pre-TDC cylinder pressure, also increases IMEP by the reduction of negative torque. Or it can work against the piston as it approaches TDC during combustion.

Long rod combinations usually like intake manifold passages (actually heads and manifold) that help boost flow rates not provided by more rapidly descending pistons associated with shorter rods. So in addition to adjusting valve timing and lift patterns to match changes in piston speed needed to increase volumetric efficiency for increased rod length, port section areas and even carburetor sizing can be used to help restore reduced flow rates.

There is also the issue with reduced piston side-loading with long rod use. This reduction in friction horsepower has been attributed to power gains, especially when piston speed increases beyond about 2,500 feet/second. Improved ring life with long rods has also been claimed by some engine builders.

So while none of this month's Enginology was intended to advocate the use of short or long connecting rods, it emphasizes the importance of contemplating other engine functions that required consideration when making material changes to the rate of piston travel as a direct function of crankshaft angle. You will find that knowledgeable parts manufacturers, relative to the subject of connecting rod length, generally have a store of information linking how their components can affect an engine's ability to capitalize on rod length changes. If they don't, you may want to consider finding manufacturers who do. The concept of functional parts integration isn't without basis.

before you buy components talk to both the vendors and your machine shop of choice , you damn sure don,t want mis-matched components and clearances.
you need to measure accurately, know what your current block will function correctly with and pay attention to clearances and other details that make or break the engines potential durability and power potential.

enigma57 · Feb 17, 2011

Re: bore to stroke ratio

Thanks, Grumpy! As it happens, I am right in the middle of a long stroke small block build and I will certainly read over all the links you posted before proceeding.

Best regards,

Harry

grumpyvette · Feb 19, 2011

Re: bore to stroke ratio

Figuring Compression Height of a piston

The compression height is the distance from the center of the wrist pin hole to the top deck of the piston. (see attached pix)

Custom pistons are available in any practical compression height to compensate for stroker or de-stroker cranks, long rods, or blocks which have been milled excessively, etc. Winston Cup & Busch motors usually have a very low or small compression height. (1.245 to 1.12 inches) The reason is that they have a shorter than stock stroke with a longer than stock rod length.
Ive always preferred to keep the piston pin out of the lower oil ring groove if I can, a compression height in the 1.5-1.375 range or larger will frequently allow that , but obviously each piston supplier will have a slightly different design, and obviously the applications will differ so you may be required to select something thats not always your ideal compromise
keep in mind theres some leeway, in that head gaskets can be used with different thicknesses to maintain a set quench distance, so if a piston sticks lets say as an example .010 out of the bore a .050 thick head gasket could be selected to maintain a .040 quench, if the pistons .015 down the bore, a thinner .025 head gasket could be used, so if your calculations show you need a 1.4" compression height a 1.390-1.410 could be used in most cases giving you a bit more choice selecting pistons

1st thing you need to know is the block height. To find this you need to measure from the crankshaft center line to the deck (cylinder head mounting surface) of the block.

2nd Next thing is rod length. To determine exact rod length, you should have a good pair of calipers to measure with. Measure the size of the rod bearing opening (big hole) and the size of the wrist pin opening, and divide them in two (or one half) Finally, determine the distance between the two openings (center of the rod) and add the half you just calculated. That gives you the rod length. It comes out to be the distance between the center of the two holes.

Finally you need the stroke length.

Stroke length is;

twice the distance from the center line of the crankshaft main bearing journals to the cente rline of the connecting rod journals or ;

It is also the distance the piston moves up and down in the cylinder

Now that you have all the info, you can calculate the compression height of the piston;

To calculate the compression height, use the following formula:

Block Height minus 1/2 the crank stroke, minus the rod length, minus the deck clearance (amount piston is "in the hole").

For example, a 350 Chevy engine with a stock 3.480 stroke, stock length 5.700 rod, standard .017 deck clearance and standard 9.025 block height would be:

3.480 stroke divided by 2 = 1.740

9.025 - 1.740 - 5.700 - .017 = a compression height of 1.568.

if you were building a 496 BBC the deck height on the standard blocks 9.8"
rods are typically 6.385"
stroke is 4.25", so half the stroke is 2.125" plus 6.385" rod length, subtracted from 9.8" deck height, =1.29" piston compression height

https://www.uempistons.com/index.php?ma ... iston_comp

related info

viewtopic.php?f=52&t=4081&p=12278&hilit=quench#p12278

http://garage.grumpysperformance.co...-about-your-potential-dream-bbc-combos.14607/

viewtopic.php?f=52&t=727

http://www.kb-silvolite.com/calc.php?action=piston_comp

viewtopic.php?f=53&t=3061&p=8095&hilit=piston+suppliers#p8095

viewtopic.php?f=53&t=2208&p=5942&hilit=piston+suppliers#p5942

viewtopic.php?f=69&t=2645&p=6834#p6834

http://www.lunatipower.com/Tech/Pistons ... eight.aspx

enigma57 · Feb 20, 2011

Re: bore to stroke ratio

Great info, Grumpy! The diagrams make it much easier to visualize the relationship of the various component parts that make up an engine and how they work together.

Thanks,

Harry

grumpyvette · Feb 21, 2011

Re: bore to stroke ratio

quote=enigma57

"If I replaced the entire reciprocating assembly with a crank having 1/8" less stroke and went to longer 6" rods and pistons having a comp. height of 1.0875", it would improve rod/stroke ratio somewhat.....

4.000" stroke / 5.850" rod = 1.462:1 (My present combo)
3.875" stroke / 6.000" rod = 1.548:1 (New combo)
3.75" stroke / 6.000" rod= 1.6:1

Or I could destroke to 3.300" and use 6.2" rods along with my present 4.125" bore pistons having 1.170" comp. height......

3.300" stroke / 6.200" rod = 1.878:1 (This combo should rev easily and nets 352.8 cu. in. displacement)
3.000" stroke / 5.700" rod = 1.900:1 (stock 265,283,302)"

ok lets say youve got a new dart block with a 4.125" bore and your selecting a crank, youve narrowed the choices to a 3.30", a 3.75" and a 4" stroke crank combo

I think your placing a bit more concern on rod to stroke ratio and rod angle than is warranted, under the conditions.
every choice has a compromise in some area, and as the rpms go up so does the stress on the rotating components and valve train.

keep in mind that your likely to produce about 1.25-1.35 hp per cubic inch with a well tuned combo like you've described , lets assume the larger combo only makes 1.25 hp per cubic inch and a de-stroker with its better rod angle makes a full 1.35:1 cubic inch

427 x 1.25=534(4" stroke)
372 x 1.35=502 (3.75" stroke)
352 x 1.35=476 (3.30 stroke)
but keep in mind the larger engines going to have about a 30-60 ft lb or more torque advantage over the smaller displacement combos over most of the rpm range and that power will come in at about 400rpm-600rpm lower and its responsive low and mid rpm torque that tends to be far more important than peak hp on a street car.
and its going to be cheaper and easier to maintain valve train control,at 6300rpm and below a good hydraulic roller cam,possibly with a rev kit should control the valve train,
yes there's some advantage in the better rod stroke ratio, but it will quickly be compromised by the need to rev the engine to higher rpms and valve train control issues , in many combo, less say your limiting the engine to 4200fpm in piston speed?
a 4" stroke=6300rpm . or about the max rpm any hydraulic lifter valve train is likely to function reliably
a 3.75" stroke=6700rpm =surely solid lifter rpm with a stud girdle
a 3.5" stroke=7200rpm=surely solid lifter rpm =shaft rocker time
a 3.3" stroke=7600rpm=surely solid lifter rpm =shaft rocker time
I get asked why the 301/302-327-331 sbc engine, is just not seen as commonly any more, the basic reason is the 283-327 they were built from is no longer as common as the current 350 basic core engine the 383-396-401 gets built from, as the 350 sbc is far more common.
just some info guys....there's a GOOD REASON why the 302 is less than popular compared to a 383-401 stroker built from a 350 basic block.
THERE'S NO way a 302 with its 3" stroke and the higher stress on the valve train that rpms over 7000rpm that the 302 sees will match the results and dependability a 383-396-401 stroker combo with its 3.75"-3.875" stroke and under 6500rpm valve train stress will produce
lets say a 302 can produce 1.25-1.4 hp per cubic inch, you can do the same with a 396 sbc
your looking at say 410 hp for the 302 and a similar 396 sbc costing almost the same will produce 535 hp with the same hp per cubic inch WITH LOWER VALVE TRAIN STRESS, its a FACT your far more likely to have valve train problems at over 6500rpm than under that rpm
there's also a much faster ramp up on the torque curve with the larger displacement.
we USED to build 301-327-331 sbc when the cylinder heads flow limited the effective displacement that could effectively be fed, those days are long gone, with the current aftermarket heads.

example

http://airflowresearch.com/articles/article031/A-P1.htm

http://www.chevytalk.org/fusionbb/showt ... id/131229/

http://www.bracketmasters.com/small_blo ... 383_cu.htm

http://airflowresearch.com/articles/art ... A14-P1.htm

http://airflowresearch.com/articles/art ... A16-P1.htm

BTW USING A HYDRAULIC LIFTER VALVE TRAIN in a 302-331 SBC that's built for MAX HP,is about as useful as snow shoes on a snake

ID also point out the differences in bearing sizes and the difficulty in building good compression with flat top pistons with the shorter stroke combos

for those guys that think high rpms are the way too go....,think about this, in a correctly clearanced and balanced lower assembly,
piston speeds should almost always be UNDER 4000fpm with correctly reworked stock type parts , or 4500FPM with all forged aftermarket race quality parts, if you expect the lower assembly to live a decent life span, that's,
between 8000-9000rpm on a 302 and 6400-7200 rpm with a 383 so as you should see, its far more likely the valve train is the weak link that determines the RED LINE
since the cars engine speed is usually restricted to the rate of acceleration of the car due too the engine being locked into driving the drive train,the larger engine has a slight advantage in acceleration with equal rear gears but in the real world you'll run 3.73:1-4.33:1 rear gears with a 383 and 4.56:1-5.13:1 with a 302, making the crank acceleration rates similar, or higher with the 302.
personally Ive never seen any advantage to spinning a smaller stroke engine to higher rpms, to make power, the stress on the valve train and lower assembly tends to cause more parts failures, its a whole lot easier to control valves at 6000rpm than at 8000rpm, and it gets darn expensive when pistons kiss valves, keep the engine operating well within its safe/ low stress speed,limits and it will last far longer.
at 8000rpm the valves open and close in each cylinder 67 TIMES A SECOND, your approaching absurd inertial loads and control problems well under that at 6400 rpm where the valves open and close at 53 times a second

[/color]
the discussion about whats the best connecting rod length to stroke ratio and what rod design should be selected has been hashed thru in a near endless debate, I,d suggest you pay a great deal of attention to the quality of the connecting rods, bearings used, quench,clearances and engine lubrication, and preventing detonation, and maximize oil and coolant cooling to keep both in a reasonable range (THERE THREADS ABOUT THIS) and use an internally balanced rotating assembly, and while longer rod ratios are in theory beneficial the proven benefits are usually minimal as long as you keep the piston speeds reasonable
before I even begin,to discuss this Id strongly suggest IF your planing an engine build, that you purchase a complete matched rotating assembly, thats internally balanced from a well known manufacturer, and an SFI certified DAMPER AND FLYWHEEL OR FLEX-PLATE because any attempt at matching, miss matched components will result in zero warranty on any problem, fitting, matching or breaking in,the components

anyone who understands physics and geometry and can use a calculator or do minimal research into those questions,understands that a change in rod length will also change several other of the parameters of the engine, not only do you change the rod length, you also change rod angles, ring drag, piston weight, piston pin height, ring stack height in some cases, crank counter weigh, piston dwell, exhaust scavenging timing etc.

If you take some time and actually calculate out , or do the math,what changes happen between lets say a 5.7” rod and a 6.0” rod on a 3.48” , or 3.75"stroke crank, in a 350 or 383 sbc.. You will soon see the actual amounts of the angle changes are very minimum. Then , your forced to ask your self how or even if these small changes in rod angle will affect the engines hp/torque, and to what extent, and will the changes be beneficial or hurt your results, and Id also point out that the compression and cam timing will also effectively change your results in some cases.

yes the internet is full of claims, claims that The motor will carry the power and torque curve father up into the rpm range with a longer connecting rod.
But you are forced to ask, by how much? and is the result , because of the rod length,change or because you used totally different lighter piston with a different ring package,and in many cases changed quench or compression etc. There are sure to be other changes that were required inside an engine with a rod length change, so you can't instantly conclude that the change in connecting rod length alone made the changes (IF ANY) you see on a dyno.

I doubt its even possible to build two virtually identical engines where only the rod length alone changed, not I personally have tried to install the longer rods and try to get a rod to stroke ratio as close to 2:1 AS OTHER FACTORS ALLOW.
this rod to stroke ratio,can be built with a 6" connecting rod and 3" stroke to build a 302 with a 283 crank and using a 327 or 350 4" bore block, or the same 283 crank in a 400 larger bearing size block with custom machined bearing spacers, to build a 4.155 bore and 3" stroke combo, correctly set up these combo are known to make very good horsepower per cubic inch, but theres no question that the added cubic inches of a 3.75" stroke crank far exceeds the results even with a less desirable rod to stroke ratio.
now a 350 with a 3.48" stroke with a 5.7' rod has a 1.64 rod to stroke ratio,
a 383 with a 5.7" rod has a 1.52:1 ratio
a 383 with a 6" rod has a 1.6"1 ratio and in every case Ive ever seen the increased displacement had a far greater effect on the 383 performance than the change in rod length seemed to induce.
as to connecting rods , from a mechanical limitations point of view, the rod bolts and the area they connect tend to be the connecting rod weak point, so Id strongly suggest ARP 7/16" rod bolts in cap screw rod designs, with the (I) beam in theory having a almost non-existent strength advantage IF THE ROD MATERIAL CROSS SECTION IS IDENTICAL, which it is usually not! I would simply suggest you shop carefully ,demand a 7/16" ARP rod bolt cap screw connecting rod of the length you prefer from a quality manufacturer, scat has been my connecting rod of choice for most engine builds

SBC
SCAT I BEAM
http://www.summitracing.com/parts/sca-25700/overview/

http://www.summitracing.com/parts/sca-2 ... /overview/

SCAT H BEAM
http://www.summitracing.com/parts/sca-6570020/overview/

http://www.summitracing.com/parts/sca-6 ... /overview/

enigma57 · Feb 21, 2011

Re: bore to stroke ratio

Grumpy, your words are wise. I have a little time before I will be ready to assemble the short block and I have been giving plenty of thought to this aspect as well.

This being an engine for a road car...... With the 427 combo, I can give up some HP up top by re-gearing and keeping RPMs down, whilst still making gobs of torque in the low to mid range.

Back in 2003, a friend forwarded me a copy of a computer dyno program (Dyno 2003). Not sure how accurate these things are, but figured it would at least give some meaningful comparisons of changes in cam profile, so I ran calcs of various cam profiles having IVC that fell within a range of 8 degrees (ranging from 2 degrees earlier IVC than would result in 8.0:1 DCR to 6 degrees later IVC).

I ran cam profiles from one extreme to the other, from the very mild (and ancient) Isky 3/4 race E-4 solid flat tappet grind to the UltraDyne solid flat tappet short track cam I had Harold Brookshire grind me with wider 110 degree LSA some years back...... And several hydraulic and solid lifter cams in between.

By way of comparison, I plotted TQ and HP from 2,000 RPMs through 6,000 RPMs and also plotted average TQ and HP from 2,000 RPMs through 4,000 RPMs.

Geared as it is at present, my car will be turning 2,500 RPMs in 6th gear OD cruising at 70 MPH. HP and TQ averages for all cam grinds in the 2,000 - 4,000 RPM range were within 10 HP and 15 ft./lb. of one another...... Though peak TQ ranged from 3,500 RPMs to 4,500 RPMs and peak HP ranged from 5,000 RPMs to 6,000 RPMs, depending upon cam grind. (Given the use of the car, I have placed a self-imposed 6,000 RPM redline on this 4" stoke combo to limit piston speed to 4,000 fpm max at redline as you suggested some time ago.)

What changed most was where the engine made the most power. As expected, the milder cams made more power down low.

Interestingly, all were within 11 HP and 15ft./lb. of TQ at 3,500 RPMs. And as expected, the more aggressive grinds began pulling away from the milder cams which had made more power below 3,500. And from 3,500 RPMs to their respective redlines, each of the more aggressive grinds made up the difference between their lack of power at lower revs...... The averages from 2,000 - 4,000 RPMs being very close.

From 4,500 RPMs to their respective redlines, the more aggressive grinds pulled harder and the higher they spun, the more HP they made...... Whilst shifting TQ peak higher, but with ft./lbs. remaining very close to the numbers achieved at lower revs with the milder grinds. All in all, it was a very interesting comparison.

Here are some examples, beginning with the little Isky E-4 solid lifter grind from the '50s that makes the 427 into a low RPM stump puller......

Solid flat tappet......

------RPMs----- HP ---TQ

2,000 RPMs - 189 - 497 - Cam, Isky E-4 solid, flat tappet, 216 deg. int./216 deg. exh. @ 0.050", 108 deg. LSA, 0.425" lift at valve (both)
2,500 RPMs - 242 - 508
3,000 RPMs - 296 - 519 - Peak HP - 421 @ 5,000 RPMs
3,500 RPMs - 349 - 523 - Peak TQ - 523 ft./lb. @ 3,500 RPMs
4,000 RPMs - 391 - 513
4,500 RPMs - 421 - 492
5,000 RPMs - 421 - 442 - Avg. HP - 2,000 to 4,000 RPMs, 293.4
5,500 RPMs - 408 - 389 - Avg. TQ - 2,000 to 4,000 RPMs, 512 ft./lb.
6,000 RPMs - 376 - 329

------RPMs----- HP ---TQ

2,000 RPMs - 182 - 479 - Cam, Isky RPM-300 solid, flat tappet, 228 deg. int./228 deg. exh. @ 0.050", ground on 108 deg. (not 112 deg.) LSA, 0.448" lift at valve (both)
2,500 RPMs - 235 - 493
3,000 RPMs - 292 - 511 - Peak HP - 458 @ 5,000 RPMs
3,500 RPMs - 349 - 524 - Peak TQ - 527 ft./lb. @ 4,000 RPMs
4,000 RPMs - 402 - 527
4,500 RPMs - 439 - 513
5,000 RPMs - 458 - 481 - Avg. HP - 2,000 to 4,000 RPMs, 292
5,500 RPMs - 450 - 429 - Avg. TQ - 2,000 to 4,000 RPMs, 506.8 ft./lb.
6,000 RPMs - 427 - 374

------RPMs----- HP ---TQ

2,000 RPMs - 184 - 483 - Cam, Isky 530-A solid, flat tappet, 242 deg. int./246 deg. exh. @ 0.050", 106 deg. LSA, 0.530" int./ 0.535" lift at valve
2,500 RPMs - 239 - 501
3,000 RPMs - 297 - 520 - Peak HP - 517 @ 5,500 RPMs
3,500 RPMs - 359 - 538 - Peak TQ - 548 ft./lb. @ 4,500 RPMs
4,000 RPMs - 417 - 548
4,500 RPMs - 470 - 548
5,000 RPMs - 505 - 530 - Avg. HP - 2,000 to 4,000 RPMs, 299.2
5,500 RPMs - 517 - 493 - Avg. TQ - 2,000 to 4,000 RPMs, 518 ft./lb.
6,000 RPMs - 509 - 446

------RPMs----- HP ---TQ

2,000 RPMs - 170 - 446 - Cam, UltraDyne solid, flat tappet, 252 deg. int./252 deg. exh. @ 0.050", 110 deg. LSA, 0.525" lift at valve (both)
2,500 RPMs - 223 - 468
3,000 RPMs - 282 - 493 - Peak HP - 546 @ 6,000 RPMs
3,500 RPMs - 348 - 523 - Peak TQ - 555 ft./lb. @ 4,500 RPMs
4,000 RPMs - 413 - 543
4,500 RPMs - 475 - 555
5,000 RPMs - 519 - 545 - Avg. HP - 2,000 to 4,000 RPMs, 287.2
5,500 RPMs - 546 - 522 - Avg. TQ - 2,000 to 4,000 RPMs, 494.6 ft./lb.
6,000 RPMs - 546 - 478

Hydraulic flat tappet......

------RPMs----- HP ---TQ

2,000 RPMs - 176 - 463 - Cam, Comp Cams #CS NX268H-13 ground on 108 LSA, hydraulic, flat tappet, 224 deg. int./236 deg. exh. @ 0.050", 108 deg. LSA, 0.477" int./0.490" exh. lift at valve)
2,500 RPMs - 230 - 483
3,000 RPMs - 285 - 500 - Peak HP - 497 @ 5,500 RPMs
3,500 RPMs - 345 - 518 - Peak TQ - 522 ft./lb. @ 4,500 RPMs
4,000 RPMs - 402 - 527
4,500 RPMs - 447 - 522
5,000 RPMs - 484 - 508 - Avg. HP - 2,000 to 4,000 RPMs, 287.6
5,500 RPMs - 497 - 474 - Avg. TQ - 2,000 to 4,000 RPMs, 498.2 ft./lb.
6,000 RPMs - 486 - 425

------RPMs----- HP ---TQ

2,000 RPMs - 183 - 481 - Cam, Lunati 268 VooDoo hydraulic, flat tappet, 227 deg. int./233 deg. exh. @ 0.050", 110 deg. LSA, 0.489" int./0.504" exh. lift at valve)
2,500 RPMs - 237 - 497
3,000 RPMs - 294 - 515 - Peak HP - 479 @ 5,500 RPMs
3,500 RPMs - 355 - 532 - Peak TQ - 537 ft./lb. @ 4,000 RPMs
4,000 RPMs - 409 - 537
4,500 RPMs - 455 - 531
5,000 RPMs - 478 - 502 - Avg. HP - 2,000 to 4,000 RPMs, 295.6
5,500 RPMs - 479 - 457 - Avg. TQ - 2,000 to 4,000 RPMs, 512.4 ft./lb.
6,000 RPMs - 455 - 399

------RPMs----- HP ---TQ

2,000 RPMs - 187 - 491 - Cam, Isky 274 Mega hydraulic, flat tappet, 226 deg. int./226 deg. exh. @ 0.050", 108 deg. LSA, 0.490" lift at valve (both)
2,500 RPMs - 243 - 510 - Note: 1.6 rockers raise peaks by 4 - 5 HP & ft./lb. TQ, but power at lower RPMs remains the same
3,000 RPMs - 302 - 528 - Peak HP - 478 @ 5,000 RPMs
3,500 RPMs - 362 - 543 - Peak TQ - 547 ft./lb. @ 4,000 RPMs
4,000 RPMs - 417 - 547
4,500 RPMs - 458 - 535
5,000 RPMs - 478 - 502 - Avg. HP - 2,000 to 4,000 RPMs, 302.2
5,500 RPMs - 468 - 447 - Avg. TQ - 2,000 to 4,000 RPMs, 523.8 ft./lb.
6,000 RPMs - 446 - 390

I believe you are right. Better to go ahead and build the larger displacement version. The key to keeping this long stroke engine together and keep it running for many, many miles will be to gear the car to keep RPMs down and build the engine for low and mid range torque.

Of the cams I ran through the desk top dyno, these three came out on top. I have ranked them below based upon how each did when comparing average TQ and HP produced between 2,000 and 4,000 RPMs (the engine speeds this engine will see the most out on the highway). Surprisingly, the little Isky 274 Mega short track hydraulic flat tappet grind came out on top with my engine combo....... Followed by the Isky 530-A short track solid flat tappet grind and the Lunati 268 VooDoo hydraulic flat tappet street cam......

Isky 274 Mega hydraulic, flat tappet, 226 deg. int./226 deg. exh. @ 0.050", 108 deg. LSA, 0.490" lift at valve (both)

Peak HP - 478 @ 5,000 RPMs
Peak TQ - 547 ft./lb. @ 4,000 RPMs

Avg. HP - 2,000 to 4,000 RPMs, 302.2
Avg. TQ - 2,000 to 4,000 RPMs, 523.8 ft./lb.

Isky 530-A solid, flat tappet, 242 deg. int./246 deg. exh. @ 0.050", 106 deg. LSA, 0.530" int./ 0.535" lift at valve

Peak HP - 517 @ 5,500 RPMs
Peak TQ - 548 ft./lb. @ 4,500 RPMs

Avg. HP - 2,000 to 4,000 RPMs, 299.2
Avg. TQ - 2,000 to 4,000 RPMs, 518 ft./lb.

Lunati 268 VooDoo hydraulic, flat tappet, 227 deg. int./233 deg. exh. @ 0.050", 110 deg. LSA, 0.489" int./0.504" exh. lift at valve

Peak HP - 479 @ 5,500 RPMs
Peak TQ - 537 ft./lb. @ 4,000 RPMs

Avg. HP - 2,000 to 4,000 RPMs, 295.6
Avg. TQ - 2,000 to 4,000 RPMs, 512.4 ft./lb.

* The Isky 530-A solid lifter grind made the most HP at peak and nearly the same TQ at peak as the Isky 274 Mega hydraulic.

* The Lunati 268 VooDoo hydraulic made nearly the same HP at peak as the Isky 274 Mega hydraulic.

* What I like about the 274 Mega is that it not only made more average power where I will need it most out on the road...... It made peak TQ and HP numbers very near to the others, but at 500 fewer RPMs.

What do you think?

Best regards,

Harry

grumpyvette · Feb 22, 2011

Re: bore to stroke ratio

the isky looks good but Id be looking for a bit more duration and a bit tighter LSA,all your selections will work with obvious various power curve changes, but Id concentrate on maximizing the 3500rpm-5800rpm torque band
try these cams with 1.6 rockers, with that bore stroke and displacement and knowing what your intended use is Id be looking to find a cam with about a 105-107 lsa.236/242-to-239-245 duration and about a .490-550 lift to make a good compromise between power and durability while maintaining low valve train stress
keep in mind that longer stroke and large displacement will react well to a tight lsa and a good deal of overlap but youll want to select the duration to maximize the mid and upper rpm power as the low rpm power should not be much of an issue, yet limit the duration to maintain at least decent low rpm drive ability,remember there's a big difference between a N/A cam used in a naturally aspirated engine and a super charger or nitrous design cam,that would have a wider lsa.
as always why not talk to the cam manufacturer and get their input and talk to them about gearing, rpm power bands etc.and your better off going with a slightly milder cam than over camming the combo, but a 427 sbc needs to breath and it takes some duration and overlap to do that efficiently,keeping in mind your goals, Id suggest and air gap dual plane intake, 750-800cfm cfm carb and long tube 1 3/4 headers
your not building a 350 so you'll need a good deal more cam, than a similar 350 build would require, but don,t get crazy, seeking peak numbers, its maximizing BOTH average torque and peak hp that matters most, don,t forget its the headers,heads, and intake that will also have a noticeable effect on the combo results.
and it only takes about 60hp or less to cruise, at 70mph at part throttle, and you don,t need off idle tire smoking torque, but you do need impressive acceleration from about 3500rpm up to 6000rpm

http://www.crower.com/products/camshaft ... -3956.html

http://www.crower.com/products/camshaft ... -3967.html

BTW
http://www.crower.com/cam-card-finder/

click, enter part number

related info

BTW the DD DYNO software tends to favor the wider LSA selection more than real world experience suggests is valid in my experience and over state the low rpm tq, but the peak hp numbers are usually reasonably close

grumpyvette · Feb 23, 2011

Re: bore to stroke ratio

View attachment 16720

http://garage.grumpysperformance.com/index.php?threads/thank-you-grumpy-and-team.17583/

calculate required octane for compression ratio

What else influences your car's octane requirements? IF YOU DON,T LIKE READING SUB-LINKS, AND LOOKING AT CHARTS , AND DOING A BIT OF MATH 'AND INDIVIDUAL CALCULATIONS, YOUR UN-LIKELY TO BENEFIT FROM MOST OF THE THREADS, ON THIS WEB SITE! LIKE IN MOST AREAS ITS KNOWLEDGE AND THE ABILITY TO THINK...
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Performance Tech | Compression Ratio 101 Part:2 - DSPORT Magazine

Opinions are like assholes and everyone has one. Look on a forum, blog, Instagram or YouTube account and you can find a number of “engine builders” sharing their thoughts and feelings on the best compression ratio for a particular engine or application. If you take away anything more than the […]

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thinking through where the power of combustion can be Enhanced

theres a long list of factors that have to be considered and balanced for the internal combustion engine to make better power ,one major factor is the type of fuel used and the fuel/air ratio and its efficient combustion, if you want to boost power you need to more effectively increase...
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Wallace Racing - Calculate Boost Compression Ratio

Effects of a longer Rod
* Less rod angularity reduces wear.
* Lower piston velocity and acceleration reduces tensile loading of the rods.
* Less ignition timing is required which resist detonation.
* Compression can be increased slightly before detonation is a problem.
* Less intake runner volume is required and high rpm breathing is improved.
* Reduces scavenging at low rpm (weaker low RPM power).
* Longer TDC dwell time. (high RPM efficency).

Effects of a shorter Rod
* Increased rod angularity increases wear.
* Increased piston velocity and acceleration increases tensile loading of the rods.
* Increases scavenging at low rpm (increased low RPM power).
* Reduced TDC dwell time. (Reduced high RPM efficiency).

What they forgot to mention about the long rod is that the positive gain at TDC, is partially offset by wasted dwell time at BDC. The other problem is that on some piston designs, is the close proximity of the wrist pin hole and the bottom oil ring rail, on the piston, can cause flexing in the ring and less effective oil control.
below They used a 3.5" stroke for both rods, which is very close to a 350's 3.48" stroke.
As the graph shows, even 2" longer rod does not perform miracles, the better rod ratio has some effect but nothing thats going to totally make or break a combos effective power curve provided you keep the piston speeds well within the component strength limitations.
as stated before with basically stock components 4000fpm in piston speeds a good compromise, and with all forged and balanced components 4200fpm is doable, even 4500fpm for a second or two can be tolerated in some combos but stress goes up rapidly as rpms increase and stress is cumulative.

Bbc Related & Links And Useful Info

a few useful links, and sub links videos, and tips to look over yeah, increased displacement helps and building a killer BBC old school, for your car can be both cost effective and produce impressive results some of the most effective, cost per hp and efficient combo's , will be the 496...

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grumpyvette · Feb 23, 2011

Re: bore to stroke ratio

http://www.iskycams.com/techinfo_index.html

Rod Lengths/Ratios: Much ado about almost nothing.

Why do people change connecting rod lengths or alter their rod length to stroke ratios? I know why, they think they are changing them. They expect to gain (usually based upon the hype of some magazine article or the sales pitch of someone in the parts business) Torque or Horsepower here or there in rather significant "chunks". Well, they will experience some gains and losses here or there in torque and or H.P., but unfortunately these "chunks" everyone talks about are more like "chips".

To hear the hype about running a longer Rod and making more Torque @ low to mid RPM or mid to high RPM (yes, it is, believe it or not actually pitched both ways) you'd think that there must be a tremendous potential for gain, otherwise, why would anyone even bother? Good question. Let's begin with the basics. The manufacture's (Chevy, Ford, Chrysler etc.) employ automotive engineers and designers to do their best (especially today) in creating engine packages that are both powerful and efficient. They of course, must also consider longevity, for what good would come form designing an engine with say 5% more power at a price of one half the life factor? Obviously none. You usually don't get something for nothing - everything usually has its price. For example: I can design a cam with tremendous high RPM/H.P. potential, but it would be silly of me (not to mention the height of arrogance) to criticize the engineer who designed the stock camshaft. For this engine when I know how poorly this cam would perform at the lower operating RPM range in which this engineer was concerned with as his design objective!

Yet, I read of and hear about people who do this all the time with Rod lengths. They actually speak of the automotive engine designer responsible for running "such a short Rod" as a "stupid SOB." Well, folks I am here to tell you that those who spew such garbage should be ashamed of themselves - and not just because the original designer had different design criteria and objectives. I may shock some of you, but in your wildest dreams you are never going to achieve the level of power increase by changing your connecting rod lengths that you would, say in increasing compression ratio, cam duration or cylinder head flow capacity. To illustrate my point, take a look at the chart below. I have illustrated the crank angles and relative piston positions of today's most popular racing engine, the 3.48" stroke small block 350 V8 Chevy in standard 5.7", 6.00", 6.125" and 6.250" long rod lengths in 5 degree increments. Notice the infinitesimal (look it up in the dictionary) change in piston position for a given crank angle with the 4 different length rods. Not much here folks, but "oh, there must be a big difference in piston velocity, right?" Wrong! Again it's a marginal difference (check the source yourself - its performance calculator).

To hear all this hype about rod lengths I'm sure you were prepared for a nice 30, 40, or 50 HP increase, weren't you? Well its more like a 5-7 HP increase at best, and guess what? It comes at a price. The longer the rod, the closer your wrist pin boss will be to your ring lands. In extreme situations, 6.125" & 6.250" lengths for example, both ring and piston life are affected. The rings get a double whammy affect. First, with the pin boss crowding the rings, the normally designed space between the lands must be reduced to accommodate the higher wrist pin boss. Second, the rings wobble more and lose the seal of their fine edge as the piston rocks. A longer Rod influences the piston to dwell a bit longer at TDC than a shorter rod would and conversely, to dwell somewhat less at BDC. This is another area where people often get the information backwards.

In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!

Now to the subject of rod to stroke ratios. People are always looking for the "magic number" here - as if like Pythagoras they could possibly discover a mathematical relationship which would secure them a place in history. Rod to stroke ratios are for the most part the naturally occurring result of other engine design criteria. In other-words, much like with ignition timing (spark advance) they are what they are. In regards to the later, the actual number is not as important as finding the right point for a given engine. Why worry for example that a Chrysler "hemi" needs less spark advance that a Chevrolet "wedge" combustion chamber? The number in and of itself is not important and it is much the same with rod to stroke ratios. Unless you want to completely redesign the engine (including your block deck height etc.) leave your rod lengths alone. Let's not forget after all, most of us are not racing at the Indy 500 but rather are hot rodding stock blocks.

Only professional engine builders who have exhausted every other possible avenue of performance should ever consider a rod length change and even they should exercise care so as not to get caught up in the hype.

if you do a bunch of research, or connecting rod length to stroke ratios and piston speeds etc., youll find a general consensus that the ideal rod ratio is near 1.9:1 on the stroke length,so something like a 3' or 3.25' stroke with a 6" connecting rods near the ideal , i also have built enough engines like a 406 chevy with a 5.7' rod or a 540 big block CHEVY with 6.385" rods that have closer to a 1.5:1 ratio that made exceptionally good power,to know that I read thru this thread and many other similar threads about rod to stroke ratios, that the phrase's

"TEMPEST IN A TEA POT"
"MOUNTAIN OUT OF A MOLE HILL"
BOTH COME TO MIND!"
yes theres measurable advantages to be gained in well matched component selection,and careful assembly, but I think the degree of concern here seems a bit excessive compared to the potential gains you might expect from the difference in parts being selected, compared to several other areas that potentially effect engine power that you might be concerned with.

connecting rod & rod length too stroke info

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reliable source of info

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calculate required octane for compression ratio​

Performance Tech | Compression Ratio 101 Part:2 - DSPORT Magazine​

thinking through where the power of combustion can be Enhanced​

Administrator

calculate required octane for compression ratio

Performance Tech | Compression Ratio 101 Part:2 - DSPORT Magazine

thinking through where the power of combustion can be Enhanced