What con-rods would you buy?

bvlahov

Member
I just bought a set of used Carrillos with 7/16 Carr bolts.
Those should be as good as you can buy. For $264 I just
didn't want to pass on that. New ones are $2100+.

I'll have them inspected when they arrive, install
new bushings, have them resized if necessary and I think
that I should be more than safe
for my goals (550-600chp/7500rpm).

It's allready over now but I'd like to know what would you buy
and why?! Did I make a mistake when I bought used rods?
Lets say that this would be 7500 rpm, 550-600 crank hp engine.
I'm talking about 4340 forged 6" H-beam rods.

1. Brand new Manley rods that are somewhere in $600 range.

2. Brand new Eagle rods - $520 range

3. Used Carillo rods for $600 ($2000 for new)

4. Something else? (manufacturer and price?)

5. New Callies Compstar rods - $550

6. New K1 (by Carillo) billet H-beam - $400 or $465 (with ARP 2000 bolts)
 
If you got a set of those rods in good shape at that price you, probably got a GREAT DEAL even if they are used rods, naturally youll need to have them checked by a good machine shop before re-use.

The better 4340 connecting rods from most manufacturers themselves rarely fail, its the bolts that stretch or the valve train,control ,lubrication,and clearance issues or detonation, that causes the problems that get mistakenly listed as rod failures.

As with most components you tend to get what you pay for to a great extent and companys like (CROWER, CARRILLO,and OLIVER will gladly provide you with much stronger AND MORE EXPENSIVE) connecting rods , good moderately priced connecting rods are available from SCAT

http://www.oliverracingparts.com/

https://www.crower.com/connecting-rods.html


http://www.cp-carrillo.com/

http://www.scatcrankshafts.com/rods/chevy-rods/
http://www.carrilloind.com/

http://www.oliverconnectingrods.com/

http://www.lunaticams.com/Category.aspx?id=12

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

http://www.crower.com/pdf/177-180.pdf

ALL THE ABOVE MAKE SOME EXCELLENT CONNECTING RODS

http://www.scatenterprises.com/

http://www.eaglerod.com/

http://www.manleyperformance.com/

http://www.catpep.com/default.asp

ALL make nice and lower cost /affordable connecting rods

Now obviously when selecting a connecting rod, the stress and rpm limits and the matched components must be considered,
so OBVIOUSLY A FEW MINUTES DISCUSSING YOUR PROJECT AND TAKING THE ADVICE OF YOUR CONNECTING ROD MANUFACTURER OF CHOICE IS A GOOD IDEA!

the best connecting rod on the planets not going to survive a constant repeat high speed impact with or be expected too successfully try too compress busted chunks of pistons or valves that failed for one reason or another against a cylinder head where its expected to survive the impact stress with whats left of a piston or the head of a valve that busted off ,or that comes apart due to detonation or valve float issues.

Its been my experience that almost any rotating assembly with 4340 forged connecting rods (with 7/16" ARP bolts (L19) OR (ARP2000)if possible) are strong enough , if the clearances are correct and they were assembled according to the instructions with a rod mic, stretch gauge
arp-100-9942_w_m.jpg


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

or even the correctly used torque wrench, for most if not all street strip or even the full time race engines most guys commonly build that produce under 4500fpm in piston speeds and under 750 hp.
Almost without any exception the busted / bent/damaged connecting rods and the damage they got blamed for was the RESULT of,and not the CAUSE of,a piston or valve train failure, due too a lack of valve control, or detonation , or clearance or lubrication issues , and NOT a rod failure.

I like CAP SCREW equipped connecting rods with 7/16" (L19)or (ARP2000) rod bolts in EITHER (I)beam or (H)beam designs MATCHED to an INTERNALLY BALANCED ROTATING ASSEMBLY with reasonably long rods, 2618 forged pistons and tool steel piston pins in the bushed rods in a full floating and balanced assembly with a well designed lube system

ITS more about the difference in dwell time at TDC between 5.7" and 6" connecting rods,
and the difference in side loading, neither case shows a huge advantage , but remember max piston speed on a 383 will be near 4200 fpm,or about 6700 rpm with high quality aftermarket components like SCAT 7/16" ARP rod bolt rods


btw I would NEVER reuse the 400 sbc 5.565 rods, they are at least 40 years old,
have been through unknown millions of stress cycles,
and are well known to be a rather weak design,
that was originally designed for a lower to mid rpm torque engine,
intended mostly for pick-up trucks and luxury cars with automatic transmissions.

5.56vs5.7.png


you can purchase 5.7" connecting rods that are
easily over twice as strong as the O.E.M. connecting rods used in a stock 400 sbc
for LESS,
than it would cost to rebuild ,resize and add ARP rod bolts to the original rods


below is only one of several dozen options if your building a performance SBC
https://www.summitracing.com/parts/sca-25700716

scat5.7r.png

scat5.7r1.png

srp400.png

now you can look here
http://www.rustpuppy.org/rodstudy.htm

Piston movement was computed by simulating the crankshaft/connecting rod/piston assembly in several precise engineering drawings (DesignCad) and then determining the exact amount of piston movement for each of 256 divisions of one rotation.



The piston movement data was then used as an input vector in a MathCad program to calculate velocity, acceleration, and dynamic forces.



The simulation of an infinitely long connecting rod, which imparts true harmonic motion to the piston, is the starting point.



The motion generated by a finite length connecting rod is quite distorted by comparison. It has much more velocity and acceleration at the top of the stroke compared to the bottom. A graph of the movement is peaked at the top of each cycle and rounded and flattened at the bottom. This is caused by the rod angle increasing and pulling the piston down and adding to the motion caused by the crankshaft rotating down from top dead center. At the bottom as the rod journal slows the angle decreases. This retards the movement of the piston by subtracting the rod angle component that was added at the top of the stroke from the crankshaft movement component at the bottom of the stroke.



Compression and combustion pressures are in opposition to the inertial forces so the top of exhaust and intake strokes generate the largest forces on the rod.





1) Maximum Piston Acceleration



This table is for a 3.75" stroke used in a 400 0r 383 small block Chevy engine.

------infinite rod--------6.0" rod---5.7" rod---5.565" rod

5000rpm 1332G 1749G 1776G 1790G

6000rpm 1933G 2525G 2558G 2578G

7000rpm 2631G 3437G 3482G 3509G



Percent difference due to rod length in above table.

Difference between 6" rod and 5.565" rod 2.34%

Difference between 6" rod and 5.7" rod 1.54%

Difference between 5.7" rod and 5.565" rod 0.79%



This table is for a 3.48" stroke used in a 350 or 305 small block Chevy engine.

------infinite rod---------6.0" rod---5.7" rod

5000rpm 1240G 1600G 1623G

6000rpm 1786G 2305G 2338G

7000rpm 2432G 3138G 3182G





2) Maximum Connecting Rod Dynamic Load (Tension)



This table is for a 3.75" stroke used in a 400 or 383 small block Chevy engine. The forces are based on the weight of the piston and pin assembly and do not include the percentage of force generated by the acceleration of the end of the connecting rod. The reference piston is the stock replacement Silv-O-Lite piston for a 400 engine.



------infinite rod-----------6.0" rod-----5.7" rod----5.565" rod

5000rpm 2249LBS 2938LBS 2976LBS 3000LBS

6000rpm 3239LBS 4232LBS 4287LBS 4320LBS

7000rpm 4409LBS 5769LBS 5834LBS 5849LBS



Percent difference due to rod length in above table.



Difference between 6" rod and 5.565" rod 2.34%

Difference between 6" rod and 5.7" rod 1.54%

Difference between 5.7" rod and 5.565" rod 0.79%





3) Maximum Rod Angularity



This is the angle the connecting rod makes with the axis of the cylinder bore at 90 degrees after top dead center (maximum excursion from bore axis. This measurement is for the 3.75" stroke of the 400 and 383 only.



6.0" rod-----18.21 degrees

5.7" rod-----19.20 degrees

5.565" rod-19.69 degrees





4) Cylinder Wall Load



Percentage of compression and combustion force against the top of piston transmitted to the major thrust face of the piston and then to the cylinder wall.



This table is for the 3.75" stroke.

6.0" rod----32.89%

5.7" rod----34.83%

5.565" rod-35.64%



This table is for the 3.48" stroke.

6.0" rod---30.31%

5.7" rod---32.05%





5) Piston Speed



Maximum piston speed for the 3.75" stroke at 5000 rpm.



Infinite rod---81.68 feet per second, 55.69 MPH

6.0" rod------85.64 feet per second, 58.4 MPH

5.7" rod------86.01 feet per second, 58.6 MPH

5.565" rod---86.20 feet per second, 58.8 MPH





6) Effective Stroke



Because of the mechanical advantage provide by the toggling effect of the rod the shorter rods act as if they were in a longer stroke engine at the top of the stroke. This effect would make the short rod engine rev faster from 2000 to 4000 rpm and the circle track people claim that acceleration out of the turns is significantly improved with the shorter rod. In all other factors the longer rod comes out superior...



Effective stroke as compared to the infinite rod model for the 3.75" stroke.



infinite rod-=- 3.75"

6.0" rod------- 4.20"

5.7" rod------- 4.23"

5.565" rod---- 4.25"



Note that the differences are subtle...





7) Dwell Time



This measurement is of the number of crankshaft degrees the piston is within 0.250 inches of top dead center. It is the subject of much conjecture and controversy in the automotive literature.



This table is for a 3.75" stroke used in a 400 0r 383 small block Chevy engine.



Infinite rod---59.853 degrees

6.0" rod------52.397 degrees

5.7" rod------52.071 degrees

5.565" rod---51.915 degrees



Percentage difference in dwell time between the 6.0" rod and the 5.7" rod is 0.626%.



Percentage difference in dwell time between the 5.7" rod and the 5.565" rod is 0.3%.



Percentage difference in dwell time between the 6.0" rod and the 5.565" rod is 0.928%. (Still less than 1 percent)





This table is for a 3.48" stroke used in a 350 or 305 small block Chevy engine.



Infinite rod---62.188 degrees

6.0" rod------54.929 degrees

5.7" rod------54.605 degrees



Percentage difference in dwell time between the 6.0" rod and the 5.7" rod is 0.593% at the 3.48" stroke.

at first the difference in listed amounts seem nearly meaningless,
but the piston changing directions at nearly 110 times PER SECOND
means the minor differences in stress compound rather quickly and over time theres a measurable reduction in stress and a minor but measurable advantage to the longer rods.
the 1/2%-to-2% difference in the connecting rod length, side load, dwell time and effective pressure per degree of rotation, the longer rod length gains you adds up over time
remember theres almost no effective pressure forcing the piston down on the power stroke after about 35 degrees past TDC , so your power is derived during less than 5% of the engines rotation,(remember theres 720 degrees in a cycle )
Cylinder-Pressure-Lrg.gif

pistonposition2a.jpg

EXFLOWZ4.jpg


exhaustpressure.jpg


vechart.gif


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
0704ch_15_z+chevy_big_blocka.jpg

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

http://garage.grumpysperformance.com/index.php?threads/resizing-connecting-rods.16415/#post-99747

0704ch_14_z+chevy_big_block+.jpg

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

hrdp_0704_59_z+piston_tdc_diagram+.jpg

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

bbcdht.png

pinht1.png

pinht2.png


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.

496cmph1.png

496cmph2.png



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
66962.jpg

66797.jpg


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!

enginerebuild128.JPG


https://mobiloil.com/en/article/car...w-to-assemble-an-engine-part-2-the-bottom-end

http://garage.grumpysperformance.co...ed-holes-in-bearings-shells.10750/#post-53298

https://mobiloil.com/en/article/car...w-to-assemble-an-engine-part-2-the-bottom-end

http://garage.grumpysperformance.co...d-side-clearance-dont-assume.4690/#post-12702

http://garage.grumpysperformance.co...nk-durring-short-blk-assembly.852/#post-39417

http://www.hotrod.com/articles/0901phr-less-expensive-big-block-chevy-engine/

http://garage.grumpysperformance.com/index.php?threads/measuring-rod-and-pin-heights.3760/#post-9968

http://garage.grumpysperformance.com/index.php?threads/deck-height-problems.3048/#post-8048

http://garage.grumpysperformance.com/index.php?threads/quench-squish.726/#post-1023

http://garage.grumpysperformance.com/index.php?threads/sealants-and-threads.805/#post-71928

http://garage.grumpysperformance.com/index.php?threads/head-gasket-related.1859/#post-50617

https://www.uempistons.com/index.ph...e=deck&zenid=823ce2c9e2ffa691864d832c10107df0

https://www.uempistons.com/index.php?main_page=calculators&zenid=823ce2c9e2ffa691864d832c10107df0



related

http://garage.grumpysperformance.co...cranking-pressure-calculator.4458/#post-61262

http://garage.grumpysperformance.co...sure-hurting-your-combo.495/page-2#post-56504

http://garage.grumpysperformance.co...ng-combustion-chambers.2630/page-2#post-54344

http://garage.grumpysperformance.co...ing-parts-and-a-logical-plan.7722/#post-51341

http://garage.grumpysperformance.co...cranking-pressure-calculator.4458/#post-50454

P12CHARTS.jpg

http://www.jepistons.com/cat/je/auto/

http://www.arp-bolts.com/catalog/Catalog.html


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)

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


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
p117194_image_large.jpg


Tightening connecting rod bolts while measuring bolt stretch provides a much more accurate method of achieving proper bolt preload and clamping force.
the stretch gauge will tend to give a more accurate and consistent result and the manufacturer of the connecting rods in this case specifies a bit different torque setting than the bolt manufactuer




157191.jpg

stock

157195.jpg


better aftermarket

these links may help

http://www.scatcrankshafts.com/rods/chevy-rods/

http://www.scatcrankshafts.com/about-crankshafts/chevy-crankshafts/

http://www.scatcrankshafts.com/rotating-assembies/chevy-rotating-assemblies/
 
Last edited by a moderator:
Thank you very much for such detailed post.

I've bought these rods because in my opinion (and I may be wrong),
it's better to use high quality components (even used if they're
checked to be good) than lower quality.
I have also bought Callies Dragonslayer crank (used), and I could've
bought new forged Eagle for even less money.
But when i did research on crank or rod failures, it's almost impossible to
find broked Callies crank or Carrillo rod.
With Eagle, that's not the case.
I'm not saying that Eagle is junk, but in my opinion, used Callies will
allways be on top of the list over new Eagle.
Same goes for the rods.
A lot of people have different opinion, but this is my opinion.
 
youll seldom have problems with that theory, as most parts failures I see are with the components purchased with LOW PRICE rather than QUALITY being the prime factor in thier sellection.
decent 4340 forged components that are correctly clearanced, ballanced and lubricated rarely just FAIL.
detonation, and loss of valve train control issues probably account for most problems, and lack of proper lubrication and cooling most of the rest if the basic configuration was properly assembled, clearances were checked and assembly ballanced and operated within reasonable limits on piston speeds. try to stay under 4500 feet per minute in piston speeds with forged components and well within the valve trains designed stability limits in rpm.

read
viewtopic.php?f=53&t=343&hilit=redline


http://www.csgnetwork.com/pistonspeedcalc.html

http://www.slowgt.com/Calc2.htm

BTW heres an article with a TON of good basic info, its slanted toward PONTIAC, but about 80% or more of the info applies to most american V8 combos

http://www.wallaceracing.com/enginetheory.htm
 
GLAD TO HELP!
these threads help almost everyone that takes the time and effort to read thru the info in the threads and sub links

BTW ON my LAST BBC build I discussed, connecting rods with the guy I was building it for, he wanted to reuse stock rods untill I pointed out the cost vs strength issues
"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.

example

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

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

YEAH! maybe.. IM paranoid but I generally spend the extra $90 for the upgraded rod bolts...and we bought the H beams above with the better bolts installed for his 427 bbc, hes been running thru the lights at 7200rpm and never had a problem

ITS ALMOST ALWAYS A BETTER IDEA to buy a matched ballanced kit with all components supplied from a single source
heres a few IVE used with good results


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

http://www.dougherbert.com/enginecompon ... 5f1f37f9e5

http://www.adperformance.com/index.php? ... ath=71_231

INTERNALLY BALLANCED (SCAT, or LUNATI, or CROWER) 4340 steel FORGED KITS WITH 7/16" ARP rod bolts and clevite (H) bearings, and forged pistons are prefered in most cases, the scat 9000 cast steel cranks work ok for mild performance applications but INSIST on 7/16" ARP ROD BOLT RODS and ID strongly suggest INTERNAL BALLANCING
 
This is definately best site for somebody who is looking for
some technical help and infos.

You did really great job with organizing this site.
 
thanks! as I get time to transfer data this site should easily quaduraple in size/info at the least, if you or anyone else has a few buddies you can get to join the site, please ask them to join as the more questions, info and input the better.
 
viewtopic.php?f=53&t=510

viewtopic.php?f=53&t=247

viewtopic.php?f=53&t=341

viewtopic.php?f=53&t=204

viewtopic.php?f=53&t=691

more info you might need

forged components are generally stronger
(IE will take abuse longer and at greater stress levels) and forged pistons are slightly more heat resistant than hypereutectic or cast
as a general rule if your going to exceed 100hp shot of nitrous or have the rotating assembly spin at near 4000 feet per minute in piston speed forged components tend to be a good investment

viewtopic.php?f=53&t=110&hilit=4032

viewtopic.php?f=53&t=343&p=1170&hilit=redline#p1170

viewtopic.php?f=53&t=204&p=239#p239
 
http://www.stahlheaders.com/lit_rod length.htm
Rod Length Relationships

You are invited to participate in this attempt to understand a part of internal combustion engines. I invite any/all criticisms, suggestions, thoughts, analogies, etc.-- written preferred, phone calls accepted from those too feeble or who have arthritis. Contributors are invited to request special computer printouts for specific combinations of interest to them.

In general, most observations relate to engines used for some type of competition event and will in general produce peak power higher than 6000 RPM with good compression ring seal as defined by no more than 3/16 CFM blowby per cylinder.

Short Rod is slower at BDC range and faster at TDC range.

Long Rod is faster at BDC range and slower at TDC range.

I. LONG ROD

A. Intake Stroke -- will draw harder on cyl head from 90-o ATDC to BDC.

B. Compression Stroke -- Piston travels from BDC to 90-o BTDC faster than short rod. Goes slower from 90-o BTDC to TDC--may change ign timing requirement versus short rod as piston spends more time at top. However; if flame travel were too fast, detonation could occur. Is it possible the long rod could have more cyl pressure at ie. 30-o ATDC but less crankpin force at 70-o ATDC. Does a long rod produce more efficient combustion at high RPM--measure CO, CO2? Find out!!

C. Power Stroke -- Piston is further down in bore for any given rod/crank pin angle and thus, at any crank angle from 20 to 75 ATDC less force is exerted on the crank pin than a shorter rod. However, the piston will be higher in the bore for any given crank angle from 90-o BTDC to 90-o ATDC and thus cylinder pressure could be higher. Long rod will spend less time from 90-o ATDC to BDC--allows less time for exhaust to escape on power stroke and will force more exhaust out from BDC to 90-o BTDC. Could have more pumping loss! Could be if exhaust port is poor, a long rod will help peak power.

D. Exhaust Stroke -- see above.

II. Short Rod

A. Intake Stroke -- Short rod spends less time near TDC and will suck harder on the cyl head from 10-o ATDC to 90-o ATDC the early part of the stroke, but will not suck as hard from 90-o to BDC as a long rod. Will require a better cyl head than long rod to produce same peak HP. Short rod may work better for a IR or Tuned runner system that would probably have more inertia cyl filling than a short runner system as piston passes BDC. Will require stronger wrist pins, piston pin bosses, and connecting rods than a long rod.

B. Compression Stroke -- Piston moves slower from BDC to 90-o BTDC; faster from 90-o BTDC to TDC than long rod. Thus, with same ign timing short rod will create less cyl compression for any given crank angle from 90-o BTDC to 90-o ATDC except at TDC. As piston comes down, it will have moved further; thus, from a "time" standpoint, the short rod may be less prone to detonation and may permit higher comp ratios. Short rod spends more time at the bottom which may reduce intake charge being pumped back out intake tract as valve closes--ie. may permit longer intake lobe and/or later intake closing than a long rod.

C. Power Stroke -- Short rod exerts more force to the crank pin at any crank angle that counts ie.--20-o ATDC to 70-o ATDC. Also side loads cyl walls more than long rod. Will probably be more critical of piston design and cyl wall rigidity.

D. Exhaust Stroke -- Stroke starts anywhere from 80-o to 110-o BBDC in race engines due to exhaust valve opening. Permits earlier exhaust opening due to cyl pressure/force being delivered to crank pin sooner with short rod. Requires a better exhaust port as it will not pump like a long rod. Short rod has less pumping loss ABDC up to 90-o BTDC and has more pumping loss from 90-o BTDC as it approaches TDC, and may cause more reversion.

III. NOTES

A. Rod Length Changes -- Appears a length change of 2-1/2% is necessary to perceive a change was made. For R & D purposes it appears a 5% change should be made. Perhaps any change should be 2 to 3%--ie. Ignition timing, header tube area, pipe length, cam shaft valve event area, cyl head flow change, etc.

B. Short Rod in Power Stroke -- Piston is higher in the bore when Rod-Crank angle is at 90-o even though at any given crank angle the piston is further down. Thus, at any given "time" on the power stroke between a rod to crank pin angle of 10o and ie. 90-o, the short rod will generate a greater force on the crank pin which will be in the 70-o to 75-o ATDC range for most engines we are concerned with.

C. Stroke -- Trend of OEM engine mfgs to go to longer stroke and/or less over square (bore numerically higher than stroke) may be a function of L/R. Being that at slower engine speeds the effect of a short rod on Intake causes few problems. Compression/Power Stroke should produce different emissions than a long rod. Short rod Exhaust Stroke may create more reversion--EGR on a street engine.

D. More exhaust lobe or a earlier exhaust opening may defeat a longer rod. I am saying that a shorter rod allows a earlier exhaust opening. A better exhaust port allows a earlier exhaust opening.

E. Definition of poor exhaust port. Becomes turbulent at lower velocity than a better port. Flow curve will flatten out at a lower lift than a good port. A good exhaust port will tolerate more exhaust lobe and the engine will like it. Presuming the engine has adequate throttle area (so as not to cause more than 1" Hg depression below inlet throttle at peak power); then the better the exhaust port is, the greater the differential between optimum intake lobe duration and exhaust lobe duration will be--ie. exh 10-o or more longer than intake Carbon buildup will be minimal if cyl is dry.

IV. DEFINITIONS

Short Rod -- Min Rod/Stroke Ratio -- 1.60 Max Rod/Stroke Ratio -- 1.80

Long Rod -- Min Rod/Stroke Ratio -- 1.81 Max Rod/Stroke Ratio -- 2.00

Any ratio's exceeding these boundaries are at this moment labeled "design screw-ups" and not worth considering until valid data supports it.

Contributors to Date: Bill Clemmons, Jere Stahl

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Connecting Rod Length Influence on Power

by William B. Clemmens

A spark ignition (SI) engine and a steam engine are very similar in principle. Both rely on pressure above the piston to produce rotary power. Pressure above the piston times the area of the bore acts to create a force that acts through the connecting rod to rotate the crankshaft. If the crankshaft is looked at as a simple lever with which to gain mechanical advantage, the greatest advantage would occur when the force was applied at right angles to the crankshaft. If this analogy is carried to the connecting rod crankshaft interface, it would suggest that the most efficient mechanical use of the cylinder pressure would occur when the crank and the connecting rod are at right angles. Changing the connecting rod length relative to the stroke changes the time in crank angle degrees necessary to reach the right angle condition.

A short connecting rod achieves this right angle condition sooner than a long rod. Therefore from a "time" perspective, a short rod would always be the choice for maximum torque. The shorter rod achieves the right angle position sooner and it does so with the piston slightly farther up in the bore. This means that the cyl pressure (or force on the piston) in the cylinder is slightly higher in the short rod engine compared to the long rod engine (relative to time).

Table 1
ROD LENGTH RELATIONSHIPS*
(with Crank @ 90 deg ATDC)

Piston Position Crankpin/Rod Angle

Stroke Rod Length Rod Angle from TDC ATDC
3.5 5.70 17.88 2.025 72.12
3.5 5.85 17.40 2.018 72.59
3.5 6.00 16.96 2.011 73.04
3.5 6.20 16.39 2.002 73.60
Table 2
ROD LENGTH RELATIONSHIPS with CRANKPIN/ROD centerline @ 90o @ 7500 rpm

Stroke Rod Length Rod Angle Piston Distance Crank Angle Piston Accel
3.5 5.70 17.07 1.487 72.93 2728.35
3.5 5.85 16.65 1.494 73.35 2504.72
3.5 6.00 16.26 1.500 73.74 2324.26
3.5 6.20 15.76 1.508 74.24 2097.27
*data from Jere Stahl

Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length listed in Table 1.

Empirical experience; however, indicates that the mechanical stress is less with the longer rod length. There are two reasons for these results. Probably the primary reason for these results is that the profile of the instantaneous velocity of the piston changes with rod length. The longer rod allows the piston to come to a stop at the top of the bore and accelerate away much more slowly than a short rod engine. This slower motion translates into a lower instantaneous velocity and hence lower stresses on the piston. Another strong effect on mechanical stress levels is the angle of the connecting rod with the bore centerline during the engine cycle. The smaller the centerline angle, the less the side loading on the cylinder wall. The longer rod will have less centerline angle for the same crank angle than the shorter rod and therefore has lower side loadings.

Classical textbooks by Obert ( ) and C.F. Taylor ( ) provide little guidance on the rod length selection for passenger or commercial vehicles other than to list the ratios of rod length to crank radiuses that have been used by various engine designs. Race engine builders using production blocks have done quite a bit of experimentation and have found many drivers are capable of telling the difference and making clear choices along with similar results from motorcycle flat track racers/builders.

Because of recent developments in computer modeling of the engine cycle by R.D. Rabbitt ( ), another factor may be critical in selecting a given connecting rod length. This new factor is the cylinder head flow capability versus connecting rod length over stroke ratio (l/r) versus engine speed. To understand this relationship, let us first review previous techniques used to model air flow during the engine cycle which as Rabbitt points out is founded on principles initiated in 1862 and refined in 1920. These theories are documented in Taylor's textbook ( ). To calculate air flow throughout the cycle these models use such parameters as mean or average inlet mach number for the port velocity and an average inlet valve discharge coefficient which compensate for valve lift and duration. In these models a control volume is used to define the boundaries of the combustion chamber. The air flow determined by the previous parameters crosses this boundary to provide air (and fuel) for the combustion process within the control volume.

However, this control volume has historically been drawn in a manner that defines the boundaries of the combustion chamber in the area of the inlet and exhaust valves as if the valves were removed from the cylinder head (ie. a straight line across the port). With the valves effectively removed, the previously mentioned average port flow and valve discharge coefficient (ie. valve restriction) are multiplied within current computer models to quantify the air flow (and fuel) delivered for each intake stroke. But, as Rabbitt points out, this approach totally ignores the effect of the air flow direction and the real effect of valve lift on the total air flow that can be ingested on each intake stroke.

Rabbitt reaches two important conclusions from his study. One, because of the direction of the air flow (angle and swirl) entering the combustion chamber, three dimentional vorticies are set up during the intake stroke. Two, that above a certain piston speed, density of the mixture at the piston face is a function of valve geometry and valve speed. Rabbitt further discusses the effect of the first conclusion as it relates to the mass of air that is allowed to flow through the port and by the valve. Vorticies can exhibit different characteristics and in general conform to two general types--large scale bulk vorticies that could be described as smooth in nature and small scale eddies that are highly turbulant.

If one can consider that the vacuum produced by the piston on its downward travel to be the energy that causes the air to flow through the port when energy losses throughout the intake tract (including losses at the valve) are at a minimum, the flow delivered to the chamber will be maximized. If the area between the piston face and the valve is also included in the consideration of flow losses, the effect of the type of vorticies created can be more easily understood. Large scale bulk vorticies comsume less energy than highly turbulent eddy vorticies. Thus, more of the initial energy from the piston's downward movement is available at the port-valve-combustion chamber interface with which to draw the intake charge into the chamber. Small scale eddies eat up energy which reduces the amount of the initial energy that reaches the port-valve-combustion chamber interface which in turn, reduces the port flow.

Rabbitt's second conclusion follows that at some higher piston speed, the vorticies within the combustion chamber (which are assumed to be large scale bulk type at low speeds) transition from the bulk type to the small scale eddy type. At this point the flow into the combustion chamber ceases to increase in proportion to increases in engine speed. It is theorized that this flow transition point can be observed on the engine power curve as the point at which the power curve begins to fall off with increasing engine speed.

As indicated earlier, piston speed is normally viewed as mean or average piston speed. Thus for a given engine, the mean piston speed increases as the rotational engine speed increases. However, in Rabbitt's model the piston speed of concern is the instantaneous piston speed during the intake stroke near TDC. For any given engine, changing the rod length to stroke (l/r) ratio changes the instantaneous piston speed near TDC. For the purposes of flow visualization, the type of vortex formed should not care whether a given instantaneous piston speed had been achieved by a given rotational speed or changing the (l/r) ratio and operating at a new rotational speed. As long as the instantaneous piston velocity is the same, the type of vorticies formed should be the same and the amount of air inducted into the cylinder should be the same.

If other factors influenced by rotational speed such as the time distance between slug of intake air flow and valve opening rates relative to the acceleration of the air slugs were ignored, one should be able to predict the location (RPM) of the peak power as a result of a change in the (l/r) ratio. Note, that even though power is a funtion of air flow and air flow should be roughly constant for the same instantaneous piston speed (neglecting the afore mentioned factors), the power may not be the same because of the lever arm effect between the crank radius and the connecting rod. (As we noted earlier, the shorter rod should have the advantage in the lever arm effect.)

In reality, the analysis must be viewed by stroke (ie intake, compression, exhaust, power) the selection of exhaust valve opening time combined with the exhaust system backpressure and degree of turbulance the exhaust port experiences. If the exhaust port has good turbulance control then you may run a shorter rod which allows you to use more exhaust lobe which reduces pumping losses on the exhaust stroke.
 
http://victorylibrary.com/mopar/rod-tech-c.htm

https://www.hemmings.com/magazine/hcc/2009/06/The-Mechanical-Advantage/1827793.html

http://www.enginebuildermag.com/2007/04/performance-connecting-rods/
link too bore vs stroke info on hundreds of engines
http://users.erols.com/srweiss/tablersn.htm
READ THE LINKS & SUB LINKS
http://www.hotrod.com/articles/connecting-rods/

http://www.dragzine.com/news/howards-racing-components-explains-dense-forged-powdered-metal-rods/

http://www.enginebuildermag.com/2008/09/connecting-rods-so-many-choices/

http://www.superchevy.com/how-to/engines-drivetrain/1510sc-howards/

http://www.enginelabs.com/engine-tech/connecting-rod-tech-forged-and-billet-steel-rods/

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

http://garage.grumpysperformance.com/index.php?threads/bearing-clearances.2726/

http://garage.grumpysperformance.com/index.php?threads/rod-bolts-rpm-vs-stress.341/

http://garage.grumpysperformance.com/index.php?threads/connecting-rod-strength-h-vs-i-beam.1168/

As with most components you tend to get what you pay for to a great extent and companys like (CROWER, CARRILLO,and OLIVER will gladly provide you with much stronger AND MORE EXPENSIVE) connecting rods , good moderately priced connecting rods are available from SCAT

http://www.oliverracingparts.com/

https://www.crower.com/connecting-rods.html


http://www.cp-carrillo.com/

http://www.scatcrankshafts.com/rods/chevy-rods/


The connecting rods are a vital link between the pistons and crankshaft. They connect the reciprocal motion of the pistons to the rotational motion of the crank. The weight of the rods is important because it affects the reciprocating forces inside the engine. Lighter weight is usually better because less weight means faster throttle response and acceleration.
But strength is even more important. Connecting rods have to be stout enough to handle all the horsepower the engine can make, and be strong enough to withstand the tension forces that try to pull the rod apart when the piston hits top dead center on the exhaust stroke. If a rod is going to break, more often than not it will fail at TDC on the exhaust stroke than at any other point in its travels. Consequently, piston weight and maximum engine rpm are more important factors to consider than how much power the engine will make when selecting a set of rods.
youll find the new POWDER METAL CONNECTING RODS have a good reputation for strength and durability , but think about this, the connecting rods are NOR rebuildable because the caps ar CRACKED off and unique the that pair of components so they can not be re-sized, the powdered metal is hard and rigid and while very strong its not very flexible, and if over stressed it won,t bend it cracks and fails
BUT keep in mind , its the connecting rod bolts, that have a thinner cross sectional area that most of the connecting rods they are used in, so its the ROD bolts that stretch,
( ID STRONGLY SUGGEST THE ARP 7/16" ROD BOLTS BE USED) and allow the bearings clearances to open up, and the extra slack, and clearance leads to reduced oil pressure and rapid bearing failure's


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Basically, you want a set of rods that are as light as possible, but are also capable of handling all the forces the engine can generate (rpm and horsepower).

If you are building an engine for a sprint car that is constantly on and off the throttle, an ultra light crankshaft with the lightest possible rods and pistons will deliver the kind of performance that works best in this application. But if you are building a large displacement, relatively low rpm, high load drag motor, truck pulling motor or a marine engine, you need the reliability of a heavier crank and the strongest possible rods.

The best advice when selecting a particular set of rods is to talk to your parts suppliers and ask them what they would recommend. Every rod supplier we interviewed for this article said rod selection depends on a number of things. First and foremost is the application. In other words, what kind of engine are you building and how will it be used? The rods that work best in an all-out drag motor probably wouldn’t be the best choice for a street performance engine. Nor would rods designed for a circle track sprint car be the best choice for a NASCAR engine or a marine endurance engine.

If you choose a set of rods based strictly on a catalog or Web site description, or you choose a set based solely on length, weight or price, you may not be making the best choice. That’s why a few minutes spent on the phone with your rod supplier can be so valuable. They may recommend a particular type of rod you hadn’t considered, or they may have some new product offerings that have not yet been added to their catalog or Web site. Catalogs get out of date very quickly, and many Web site are not updated as frequently as they should be.

ROD DESIGN
The engineers who design connecting rods know how to analyze the forces that act on rods. Years ago, the design process involves a lot of trial-and-error testing. An engineer would design a rod configuration, test it until it broke, then try to beef up the areas of the rod he felt were weak. Today, most of the development work is done with computers and sophisticated software. Engineers nowadays use finite element analysis (FEA) to analyze the compression and tension forces on a rod. The software creates 3-D images with color coding that indicates the areas of highest and lowest stress. This allows the engineer to visualize what’s actually happening to a rod at various loads and speeds. He can then tweak the design on his computer screen to add metal where extra strength is needed, and to remove metal from lightly loaded areas where it isn’t needed. By repeating the FEA process over and over with each design change, he can optimize the rod to deliver the best possible combination of weight, strength and reliability — in theory anyway. It still takes real world testing to validate the design. But with today’s design and analysis software, most of the work is done before a prototype part is manufactured.

One rod supplier said using FEA on their current rods allowed them to increase strength 12 to 15 percent with less than a 2 percent increase in overall rod weight.

Computer controlled numeric (CNC) machining also allows manufacturers to machine billets and forgings in ways that were previously too difficult, too time-consuming or too expensive. This allows manufacturers to offer a wider variety of rods in terms of rod length and beam construction. It also allows them to produce custom made-to-order rods very quickly. In fact, some rod suppliers say the majority of the rods they sell today are custom order rods rather than standard dimension rods from off the shelf stock.

Rods essentially come in two basic types: I-Beam and H-Beam. Some rod suppliers only make I-Beams, others only make H-Beams, and some offer both types. I-Beam rods are the most common and are used for most stock connecting rods as well as performance rods. I-Beam rods have a large flat area that is perpendicular (90 degrees) to the side beams. The side beams of the rod are parallel to the holes in the ends for the piston pin and crank journal, and provide a good combination of light weight, and tensile and compressive strength. I-Beam rods can handle high rpm tension forces well, but the rod may bend and fail if the compressive forces are too great. So to handle higher horsepower loads, the I-Beam can be made thicker, wider and/or machined in special ways to improve strength.

Rod suppliers produce a number of variants on the basic I-Beam design. The center area may be machined to create a scalloped effect between the beams, leaving a rounded area next to both beams that increases strength and rigidity much like the filets on a crankshaft journal. These kind of rods may be marketed as having an “oval-beam”, “radial-beam” or “parabolic beam” design.

H-Beam rods, by comparison, are typically designed for engines that produce a lot of low rpm torque. This type of rod has two large, flat side beams that are perpendicular to the piston pin and crankshaft journal bores. The center area that connects the two sides of the “H” together provides lateral (sideways) stiffness. This type of design can provide higher compressive strength with less weight than a comparable I-Beam, according to the suppliers who make H-Beam rods. That’s why H-Beam connecting rods are often recommended for high torque motors that produce a lot of power at low rpm (under 6,000 rpm). Of course, an I-Beam rod can also be strengthened to handle almost any load but it usually involves increasing the thickness and weight of the rod and/or using a stronger alloy.

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STOCK CONNECTING RODS
Over 60 percent of late model connecting rods are powder metal I-beam rods. Powder metal (PM) rods are made by compressing powered steel in a mold and then heating the mold to a temperature where the powder melts and fuses into a solid part. This method of manufacturing allows parts to be cast to very close tolerances. This reduces the amount of machining needed to finish the rod, which lowers its cost. Powder metal casting also allows the ingredients in the steel alloy to be combined in ways that are impossible with conventional metal casting techniques, and the finished parts have less internal stress as a result of the fusing process. PM rods can also be up to 20 percent lighter than a comparable rod made of forged steel. Only one aftermarket rod supplier (Howards Cams) currently offers performance rods made of powder metal.

The special alloys that are used to make powder metal rods allows the rod caps to be “cracked” (separated) from the rod rather than cut. Score marks are cast into the part along the rod parting line, and the cap is then sheared off in a large press. The cracking process leaves a slightly irregular surface along the parting line between the cap and the rod that is like a jigsaw puzzle and only goes together one way. The result is better cap alignment and a stronger rod when the cap is bolted to the rod.

One of the drawbacks of powder metal rods is that the caps can’t be reground to compensate for bore distortion or stretch. Consequently, if the rod bore is out-of-round or worn, the rod usually has to be replaced unless a replacement bearing with an oversized outside diameter is available.

Stock rods are typically designed for 5,500 to 6,500 rpm, and 300 to 350 horsepower in a V8 engine. In an overhead cam four or six cylinder engine, the rods may be designed to handle up to 7,000 rpm but probably only about 200 to 250 horsepower. As a rule, most stock connecting rods can handle up to 25 to 40 percent more horsepower than an unmodified engine was originally designed to produce. So for a typical budget street performance engine or a Saturday night dirt track racer, the stock rods may work just fine.

Even so, to ensure reliability the rods should always be “Magnafluxed” to check for cracks. Any flashing, burrs, nicks or other defects along the sides of the rods should also be ground off (grind lengthwise, never sideways) to eliminate stress risers that could lead to cracks and rod failure later on. Shot peening is also recommended to improve fatigue resistance. When the shot strikes the surface, it compresses the metal slightly and actually relieves stresses that might lead to cracking and rod failure.

If an engine is being built to turn significantly higher rpms than the stock motor, or to produce significantly more power (more than 40 to 50 percent), the connecting rods will probably have to be upgraded to assure adequate reliability. For a high revving engine, some type of stronger aftermarket I-Beam rods would be a good choice. For a low rpm torquer motor, either H-Beam or heavier I-Beam rods would work well.

ROD MATERIALS & APPLICATIONS
Most aftermarket performance rods are made using 4340 billet or forged steel. This is a chrome moly alloy with high tensile and compressive strength. A word of caution, though, is that all “4340” steel alloys are not necessarily the same. Heat treatments can vary, and this will affect the properties of the steel. Some rod manufacturers also tweak the alloy by adding their own proprietary ingredients to improve strength and fatigue resistance. Several rod suppliers said the 4340 steel that some offshore rod manufacturers use falls short of American Society of Metals quality standards, and is not as good a steel as they claim it is.

There is also a debate over the relative merits of “Made-in-USA” forgings versus foreign forgings that are machined in the USA or rods that are forged and finished overseas. Labor costs are far cheaper in China and other Third World countries, so there are cost advantages for suppliers who source their forgings and rods from offshore manufacturers. Patriotic and international balance-of-payment issues aside, a connecting rod that meets metallurgical quality standards, is heat treated properly, and is accurately machined to specifications is the same no matter where it comes from or who made it. The engine won’t know the difference. So as long as the rod supplier stands behind their product with their brand name and reputation, the “foreign versus domestic” rod debate shouldn’t matter.

The mistake you don’t want to make, however, is to use low priced “economy” rods in an engine that really needs a set of top quality performance rods. A growing number of rod suppliers are now offering lower cost performance rods as economical upgrades over stock rods for street engines and other entry level forms or racing. Most of these rods are made overseas (in China, primarily) and typically sell for less than $600 a set for a small block Chevy V8. The companies who sell these rods say their products are ideal for racers who otherwise might not be able to afford better rods for their engine. Consequently, these budget-priced rods allow engine builders to offer their customers more options and more affordable alternatives for upgrading an engine. For big buck racers or really demanding applications, though, these kind of rods would not be the right choice. You would want to use a set of top-of-the-line performance rods that are capable of handling the highest loads.

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Over the past couple of years, the price of high quality steel as well as many other metals such as copper and titanium has shot up dramatically for a variety of reasons (China’s exploding economy being one, the ongoing war in Iraq being another, and changes in the steel industry itself being a third reason). Some rod suppliers are now having to add a steel “surcharge” to their current prices to help offset their higher cost of materials (which doesn’t matter where they buy their steel because the higher prices are world-wide and affect everybody). The soaring cost of titanium has almost priced this metal out of the aftermarket. Some rod suppliers have discontinued making rods from titanium. Those who still offer titanium rods say the only people who are buying them today are the high end professional racing teams with deep pockets. One rod supplier said titanium has become “unobtanium” for the average racer.

Connecting rods made of light-weight titanium rods can reduce the reciprocating mass of the engine significantly for faster throttle response and higher rpms, but at a cost of up to $1000 or more per rod, who can really afford them?

Another lightweight material that has long been used for performance connecting rods is aluminum. Many drag racers run aluminum rods because they cost less than titanium and provide a good combination of lightness and strength. Most aluminum rods are fairly stout and typically much thicker than a comparable steel I-Beam rod. The added thickness may require additional crankcase clearance, and it increases windage and drag — which at really high rpm may cost a few extra horsepower to overcome. The rods also require a dowel pin to keep the bearings from spinning because the bores stretch more than a steel rod. Also, the rod itself can stretch and grow in length at high rpm. This means extra clearance must be built into the engine so the pistons won’t smack the heads.

Though aluminum rods are popular for drag racing and other high rpm forms of racing, most of the rod suppliers we spoke with do not recommend aluminum rods for street engines. Why? Because steel rods will hold up much better over the long run than aluminum rods. Aluminum rods are fine for a drag motor that will torn down after 200 runs and freshened up or rebuilt with a set of new or reconditioned rods. But for street applications or engines that have to run at sustained high speeds and loads for long period times, steel rods are usually better.

It’s interesting to note that aluminum rods are only available from a few suppliers (GRP is one), and at least one supplier who used to offer aluminum rods (Manley) has discontinued them.

Another material that is used for many high performance rods is 300M, which is a modified 4340 steel with silicon and vanadium added, plus higher amounts of carbon and molybdenum. The 300M alloy is up to 20 percent stronger than common 4340 alloys, and was originally developed for aircraft landing gear. Now it is used for high end connecting rods.

The strength and fatigue resistance of most metals can also be improved by “cryogenic” processing after the rods have been heat treated. Heat treating causes changes in the grain structure of steel that increases strength and hardness, but it can also leave residual stresses that may lead to fatigue failure later on. By freezing parts down to minus 300 degrees below zero in special equipment that uses liquid nitrogen, the residual stresses are relieved. The super cold temperatures also cause additional changes to occur in the metal that help the parts last longer and run cooler. That’s why cryogenic freezing is used on everything from engine parts to tool steels, aerospace hardware and even gun barrels.

The cryogenic process is a slow one, taking anywhere from 36 to 72 hours depending on the parts being frozen, and it must be carefully controlled to achieve the desired results. Most rod suppliers have their own cryogenic vendors who treat their rods for them. But you can also have ordinary untreated rods (even stock rods) frozen to achieve the same results.

BY THE NUMBERS
Other factors that affect the selection of rods are rod length and rod ratio. Rod length depends on the stroke of the crankshaft and the deck height of the block. If you are switching to crankshaft with a longer stroke, you are obviously going to need rods that have a shorter overall length. Even so, replacing the pistons with ones that have a higher wrist pin location can allow you to use longer rods.

Racing legend Smokey Yunick used to say that the longer the rods are, the better. His logic was based on the fact that a longer connecting rod for a given stroke allows the piston to dwell longer at TDC before it starts back down on the power stroke. This allows pressure to build longer in the combustion chamber before it starts to shove the piston down. The result is usually a broader, flatter torque curve than the same engine with shorter rods. An engine’s horsepower and torque curves depend on a lot of variables other than rod length alone. But if everything else is equal, many engine builders say longer rods produce a broader torque curve. Others disagree, and say it doesn’t really matter.

Rod suppliers say the only trend they see in rod lengths today is that there is no trend. Engine builders are buying just as many standard length rods as they are longer rods.This brings us to rod ratio, which is the length of a connecting rod (center to center) divided by the stroke of the crankshaft. The range in engines today may be from 1.5 to 2.1, but most performance engine builders are going with ratios in the 1.57 to 1.67 range. Some say that going with a rod ratio over 1.7 makes engine torque too “peaky.” Lower rod ratio numbers are typically associated with lower rpm torque motors (a 383 Chevy street motor with a stroker crank and a rod ratio of 1.52, for example), while higher rod ratio numbers tend to be high revving high horsepower motors (a 302 high revving Chevy with a rod ratio of 1.9).

Another dimension to consider is the pin offset of the rod. On most rods (except Chevy “LS” engines), the pin bores are offset slightly. The change in pin geometry reduces the stress on the piston pin and small end of the rod when the piston reaches TDC and changes direction. It also reduces the rocking motion of the piston as it passes TDC to reduce piston slap and noise.

One new trend in this area is to run rods that do not have bronze bushings in the small end. Several racing teams are running bare rods with specially plated pins to improve durability. Eliminating the bushing, they say, leaves more meat in the small end of the rod for added strength. The only drawbacks are that the fit between the rod and pin has to be much more precise, and the wrist pin has to have a wear-resistant coating to prevent wear and galling. Also, if the pin bore becomes worn or out-of-round, the rod and piston will both have to be machined to accept a slight larger diameter pin.
 
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Thanks for re-posting this. I was looking for a good explanation of long vs short rods for a while.
 
http://www.superchevy.com/how-to/engines-drivetrain/1306-high-performance-connecting-rods/

IF you do some careful shopping you'll find that decent connecting rods are available at semi reasonable prices, I would insist on 7/16" ARP rod bolts and 4340 forged steel, and suggest SCAT, as a lower cost but good value connecting rod source





Chevy V8 bore & stroke chart
I saw this online and figured I would post it..I am going to add the popular lsx strokers soon
CID BORE STROKE
262 = 3.671" x 3.10" (Gen. I, 5.7" rod)
265 = 3.750" x 3.00" ('55-'57 Gen.I, 5.7" rod)
265 = 3.750" x 3.00" ('94-'96 Gen.II, 4.3 liter V-8 "L99", 5.94" rod)
267 = 3.500" x 3.48" (Gen.I, 5.7" rod)
283 = 3.875" x 3.00" (Gen.I, 5.7" rod)
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
302 = 4.000" x 3.00" (Gen.I, 5.7" rod)
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
307 = 3.875" x 3.25" (Gen.I, 5.7" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
327 = 4.000" x 3.25" (Gen.I, 5.7" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" ('96-'01, Gen. I, Vortec, 5.7" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)
376 = 4.065" x 3.622" (2007-later, Gen. IV, "L92", Cadillac Escalade, GMC Yukon)
383 = 4.000" x 3.80" ('00, "HT 383", Gen.I truck crate motor, 5.7" rod)
400 = 4.125" x 3.75" (Gen.I, 5.565" rod)
427 = 4.125" x 4.00" (2006 Gen.IV, LS7 SBC, titanium rods)

Two common, non-factory smallblock combinations:

377 = 4.155" x 3.48" (5.7" or 6.00" rod)
400 block and a 350 crank with "spacer" main bearings
383 = 4.030" x 3.75" (5.565" or 5.7" or 6.0" rod)
350 block and a 400 crank, main bearing crank journals
cut to 350 size



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CHEVY BIG BLOCK V-8 BORE AND STROKE


366T = 3.935" x 3.76"
396 = 4.096" x 3.76"
402 = 4.125" x 3.76"
427 = 4.250" x 3.76"
427T = 4.250" x 3.76"
454 = 4.250" x 4.00"
496 = 4.250" x 4.37" (2001 Vortec 8100, 8.1 liter)
502 = 4.466" x 4.00"
572T = 4.560" x 4.375" (2003 "ZZ572" crate motors)

T = Tall Deck

ALL production big blocks used a 6.135" length rod.
High Performance Connecting Rods - Rod Report
Jake Amatisto Jul 29, 2013 0 Comment(s)
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We often talk about how easy it is to make horsepower these days, giving praise to cylinder heads and camshaft technology, but if it wasn’t for tough bottom end parts, such as the modern aftermarket connecting rod (the most abused parts in a V-8 engine, next to the wristpins), none of it would be possible. It’s because of these extremely strong components that we have the option of building as much horsepower as our imaginations/wallets allow; and that’s with an array of power adders and cubic-inch options. Even “budget” con-rods can handle horsepower that was unheard of just 10 years ago, and that’s thanks to an innovative aftermarket.

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We started looking into connecting rods for an upcoming small-block build and we realized there are quite a few options out there. From overall design, length, and processes, connecting rods these days feature some trick attributes that are in place to handle any revving, high-powered engine. Companies like Eagle Specialties, for example, started offering their products with a process that results in a gleaming finish, which they claim strengthens and helps windage. And Scat, for example, has come up with some exclusive designs too, such as their Ultra-Lite line of rods that are great for high-rpm engines. It’s innovations like these that make building a high-powered, long-lasting engine possible.

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In the following pages we delve out some knowledge from the top four manufacturers of aftermarket connecting rods, covering what’s available for all levels of performance, and even show off some of the toughest connecting rods out there for those who want to make thousands of horsepower—yep, thousands.


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Bushed or Pressed
Research connecting rods and you will find that there are two basic ways pistons are mounted to them. A bushed rod features a bronze bushing in the small end that the wristpin slides through, and requires Spirolocks or round wire locks to retain. When it comes to high performance, bushed rods are more common, however the companies listed in this article do offer both styles. A rod that requires a pressed pin takes a hydraulic press to install (factory pistons are typically pressed on), however these rods are for low performance and rarely get used in our high-performance world.

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WristPins & Retention
Here are some examples of wristpins for different applications. The pins on the left are a standard, low-carbon steel design that are typical in high-performance applications and this is what you commonly get when you order a set of high-performance pistons; however, they are different depending on application. Tapered pins, for example, are made gradually thicker toward the center of the pin; this is for high-boost and supercharged applications where tremendous cylinder pressures are forced down on the piston. The taper is to keep the weight down without sacrificing strength. You’ll notice pins also come highly polished, this adds to the strength by eliminating stress risers and imperfections in the metal. At the highest levels of racing, special low-friction coatings are used to keep the pin from galling on the piston, even in low-oil situations. The small, dark-colored pins on the left are for a NASCAR “Cup” engine from Del West and feature a DLC coating that reduces friction. In some drag race applications where massive power adders are used, such as multiple nitrous stages, some pistons are designed to use a thick, but small-diameter wristpin due to the ring package position (it’s lower to keep the top piston ring away from intense heat).

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Here are a few examples of how the pistons are secured to the rods. The clip on the left is an old design that rarely gets used anymore, followed by the more common Spirolock and on the far left, the round wire lock that we see more piston companies going with today. Anyone who’s installed Spirolocks by hand knows what a treacherous feat it can be for your thumbs, so you’ll be happy to know there are tools available that make installation less painful. The round wire locks seem to be taking the place of the Spirolock, however that’s not the latest development in hanging pistons from rods. There is also a button-style retainer that is designed to be much easier to install than these three and doesn’t require tools.

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Rod Terms:

1. Big End
2. Small End
3. Pin Bore
4. Crank Bore
5. Cap
6. Rod Bolt
7. Beam

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Chevrolet V-8 Connecting Rod Lengths
Displacement Cubic Inches Liters Rod Length (inches)
302 4.9 5.700
305 5.0 5.700
327 5.4 5.700
350 5.7 5.700
350 (LT5) 5.7 5.700
350 (LS1) 5.7 6.098
383 6.3 6.000
400 6.6 5.565
396 6.5 6.135
402 6.6 6.135
427 7.0 6.135
454 7.4 6.135
502 8.2 6.135
377 6.2 6.135


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The two basic types of rods are I-beam and H-beam. Some say H-beams look heavier, but can end up being lighter than some I-beam designs, but not in every case. Which rod design is better is an ongoing debate, and we’re not taking sides, just showing off what’s typically offered. The designation comes from when you cut the beam: the end shapes a letter. X-beam and A-beam rods also exist, but are not common in the high-performance Chevy world.

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When building large cubic-inch small-blocks, such as 427ci and larger animals, sometimes the big end of the rod contacts the camshaft and must be clearanced meticulously. Companies like Callies, however, offer rods that have been designed with this clearance in mind.

by 540 RAT » Fri Mar 01, 2013 2:54 pm

This write-up is not intended to be a chapter out of an Engineering Design Book. That would be way too long, way too involved, and way too boring for most folks here to have any interest in. Instead, this is just a general overview of how connecting rod bolts compare, and what we REALLY NEED in our motors.

Yield Strength = the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape and size when the applied stress is removed. Once the yield point is passed, the deformation will be permanent, which is considered a “failed” condition for a bolt. So, the bolt must be discarded.

Tensile Strength = the maximum stress that a material can withstand while being stretched or pulled, without starting to neck down and ultimately breaking.

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First let’s look at some typical strength values of various bolts, to get a general feel for how they compare.


Grade 2 hardware store general purpose bolt:
Yield strength = 55,000 psi
Tensile strength = 74,000 psi
Cost = a few cents each
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Grade 5 hardware store general purpose bolt:
Yield strength = 85,000 psi
Tensile strength = 120,000 psi
Cost = a few cents each
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Grade 8 hardware store general purpose bolt:
Yield strength = 120,000 psi
Tensile strength = 150,000 psi
Cost = a few cents each
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ARP 8740 chrome moly “connecting rod” bolt:
Yield strength = 180,000 psi
Tensile strength = 200,000 psi
Cost = $120.00 per set of 16 at Summit Racing Equipment, or about $8.00 each.
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ARP 2000 “connecting rod” bolt:
Yield strength = 180,000 psi
Tensile strength = 220,000 psi
ARP 2000 rod bolt material has twice the fatigue life of 8740 chrome moly rod bolt material.
Cost = $200.00 per set of 16 at Summit Racing Equipment, or about $13.00 each.
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ARP L19 “connecting rod” bolt:
Yield strength = 200,000 psi
Tensile strength = 260,000 psi
ARP L19 rod bolt material is subject to hydrogen embrittlement, and stress corrosion. It also cannot be exposed to any moisture, including sweat and/or condensation.
Cost = $200.00 per set of 16 at Summit Racing Equipment, or about $13.00 each.
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ARP Custom Age 625+ “connecting rod” bolt:
Yield strength = 235,000 psi
Tensile strength = 260,000 psi
ARP Custom Age 625+ rod bolt material has nearly 3 ½ times the fatigue life of the ARP 3.5 rod bolt material.
Cost = $600.00 per set of 16 at Summit Racing Equipment, or about $38.00 "EACH".
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ARP 3.5 “connecting rod” bolt:
Yield strength = 220,000 psi
Tensile strength = 260,000 psi
Cost = $855.00 per set of 16 at Summit Racing Equipment, or about $53.00 "EACH"!!!

So, as you can see above, hardware store general purpose bolts are considerably weaker than “purpose built” connecting rod bolts. And we won’t even bother getting into the differences in fatigue life. Suffice it to say, we CANNOT use general purpose hardware store bolts in our connecting rods.

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A connecting rod bolt’s maximum tension loads are determined by the mass of the parts involved, the rod length, the stroke length, and the max rpm. That’s it. It has absolutely nothing what so ever to do with the amount of HP being made. The max tension loads on the rod bolts will never change, no matter if you add Nitrous, a Turbo, or a Blower to an engine, as long as the short block and redline don’t change. That max tension loading occurs at TDC on the exhaust stroke as the mass involved is brought to a dead stop, and has its direction reversed. In order to change the max tension loading on the rod bolts, you’d have to change the short block configuration and/or the redline. And vacuum pulling on the rod bolts when chopping the throttle at high rpm, is not a concern. Because those affects don't even begin to build until well past TDC, which of course is "AFTER" the mass of the parts involved has already been brought to a stop, and their direction reversed.

The rod’s big end “clamp-up preload” provided by stretching/torquing the rod bolts, must always be HIGHER than the “cyclic tension load” applied to the bolts at TDC exhaust, in order to prevent rod bolt failure. And the larger the difference between the preload and the cyclic load, the better. Precision detailed "Strength Analysis" calculations can be performed using sound Engineering principles, to determine the “Margin of Safety” (MOS) between the “cyclic tension loading” and the “clamp-up preload”, to make sure you have a sufficient MOS for the engine to be reliable. I’ll spare you all the involved and complicated math, and just show you the results.

Before we go on, first a comment on “cap screw” rod bolt sizes. Your rod bolts are NOT the size you think they are. If you run 3/8” rod bolts, only the threads are 3/8”. But, the part of the bolt that matters regarding the stretch, is the shank. And the main length of the shank is only 5/16”, not the 3/8” you might have thought. And if you run 7/16” rod bolts, the threads are 7/16”, but main length of the shank is only 3/8”. So, where you are most concerned, the bolts are one size SMALLER than you thought.

And if that isn’t enough detail, you must also consider, in addition to the main section of the shank, the other diameters involved which come from the radius transition between the threads and the shank, the radius transition between the shank and the shoulder right under the bolt head flange, and that shoulder itself right under the bolt head flange. The bolts stretch the whole length between the threads and the bolt head flange. And all those individual sections contribute to the total stretch by different amounts.

So, the rod bolt “Strength Analysis” must take into account all those various diameters, as well as the length of each of those diameters. Because the stretch has to be calculated for each individual section of the shank between the threads and the bolt head flange. If this is not done correctly, the “Strength Analysis” results will simply end up being wrong and worthless. But, for the results shown below, all those details were carefully worked out for those portions of the “Strength Analysis”. So, the answers below are all accurate.

Rod bolt "Strength Analysis" performed on known real world Street Hotrods, Street/Strip cars and Sportsman Drag cars, being operated at their typical maximum rpm, indicates the following:

• An engine with a max rpm rod bolt MOS of around 125% or higher, results in the engine being as safe and reliable as a stock grocery getter, or in other words essentially bullet proof. This is our design target when planning a new build. Having a MOS higher than this can’t hurt of course, but in terms of strength requirements, there is really no added value for doing that. However, a higher MOS can help with rod bolt fatigue life, if that is critical for a particular application. More on fatigue life later.

• If you are a little more aggressive, and run a maximum rpm rod bolt MOS between 100% and 125% only “on occasion”, which limits the number of cycles at this higher stress level, you will still generally be able to keep the engine together.

• But, if you were to run a typical maximum rpm rod bolt MOS under 100%, your rod bolts will be expected to fail prematurely.

As mentioned above in the definition of Yield Strength, we CANNOT stretch our rod bolts beyond the yield point. Because once the yield point is passed, it is considered a “failed” condition for a bolt, and the bolt must be discarded. So, a typical conservative Engineering approach in most general applications is to use a preload clamp-up of about 75% of yield. That way you have a good range between the installed preload and the yield point, in case the bolts get stressed even more during operational use. However, typical engine connecting rod bolt preload clamp-up in most reliable engines, can vary from a low of about 60% of yield to a high of about 90% of yield, with 75% of yield, the sweet spot you might say, right in the middle.

Since rod bolt stretch specs have generally become the standard in High Performance engine builds, the stretch called for is more often around 90% of the yield point. Stretching to this higher percentage of yield, is used to maximize preload clamp-up, in an effort to try and help minimize rod big end distortion at high rpm, which can cause additional undesirable rod bolt bending that would add to the bolt stress.

So, this high level of stretch is a good idea from that standpoint, but at the same time, you are left with a smaller range between the installed preload clamp-up and the yield point. But, this common 90% of yield has worked out quite well in the real world for Hotrods, Street/Strip cars, and Sportsman Drag cars. Even though there is less range between the installed preload clamp-up and the yield point, the yield point in properly selected rod bolts is not typically reached in actual operation, so all is good.

You may also have noticed that through all this discussion of rod bolt strength, there has been no mention at all of rod bolt tensile strength. That’s because we CANNOT go beyond the yield strength which is reached well “BELOW” the tensile strength. So, what good is tensile strength then? For a large number of steels, there is a direct correlation between tensile strength and fatigue life. Normally, as tensile strength increases, the fatigue life increases. So, while tensile strength does not come into play during rod bolt "Strength Analysis", it is a factor in rod bolt fatigue life.

Rod bolt fatigue life is important to Road Racers because of the number of cycles they see. And rod bolt fatigue life is absolutely critical for Endurance Racers like NASCAR. And NASCAR teams do an incredible job managing the fatigue life of their rod bolts. But, for our Hotrods, Street/Strip cars and Sportsman Drag cars, rod bolt fatigue life isn’t typically a big concern, if the motors are built with the correct rod bolts in the first place. That is because these bolts won’t typically see enough cycles in their lifetime to cause a failure due to fatigue. But, with that said, it is still a good idea to keep fatigue life in the back of your mind, when it comes to choosing your rod bolts. It can be a tie breaker, in the event that multiple rod bolts are being considered for a certain build. More on that below.

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Even though there are various companies that offer rod bolts, below we will compare 5 different rod bolts offered by Industry leader ARP.

So, let’s take a look at a typical 540ci BBC motor, running steel rods with 7/16 “cap screw” rod bolts, and uses 7,500 rpm as its typical maximum, which results in a cyclic tension load on each rod bolt that = 7,280 lbs or about 3.6 tons:

• For general reference, let’s first take a look at rods installed the old school traditional way, here using ARP 2000 rod bolts that are torqued to about 75 ft lbs with original ARP moly lube.
Bolt stretch is about .005”, which = 76% of yield strength
Clamp-up preload on each rod bolt = 16,531 lbs or about 8.3 tons
Margin of Safety (MOS) for this setup = 127%, which meets our MOS design target for being safe, reliable and essentially bullet proof.

Now, for the rest of the rod bolts we’ll be looking at, we’ll preload them to the more common higher percentage of yield strength, which is typical of the stretch called for these days.

• Using ARP 8740 chrome moly rod bolts (this has the same yield strength as ARP 2000)
Bolt stretch = .006” which = 90% of yield strength
Clamp-up preload on each rod bolt = 19,686 lbs or about 9.8 tons
Margin of Safety (MOS) = 170%

• Using ARP 2000 rod bolts (this has the same yield strength as 8740 chrome moly)
Bolt stretch = .006” which = 90% of yield strength
Clamp-up preload on each rod bolt = 19,686 lbs or about 9.8 tons
Margin of Safety (MOS) = 170%

• Using ARP L19 rod bolts
Bolt stretch = .0066” which = 90% of yield strength
Clamp-up preload on each rod bolt = 21,655 lbs or about 10.8 tons
Margin of Safety (MOS) = 197%

• Using ARP Custom Age 625+ rod bolts
Bolt stretch = .0078” which = 90% of yield strength
Clamp-up preload on each rod bolt = 25,445 lbs or about 12.7 tons
Margin of Safety (MOS) = 250%

• Using ARP 3.5 rod bolts
Bolt stretch = .0073” which = 90% of yield strength
Clamp-up preload on each rod bolt = 23,821 lbs or about 11.9 tons
Margin of Safety (MOS) = 227%

As you can see above in all 6 examples, whether torqued the traditional way to a lower stretch value, or stretched to the more recently called for higher percentage of yield value, all these rod bolts are above the minimum 125% MOS target for safety and reliability. Therefore, all these configurations would operate without issue, just like a stock grocery getter. So, if a builder chooses any of these bolts or stretch values between the 127% and the 250% "Margins of Safety" above, he could NOT go wrong, no matter how much HP the motor makes. Remember that HP has NOTHING to do with the max tension loads on rod bolts.

Since most Hotrods, Street/Strip cars, and Sportsman Drag cars, with their lower number of cycles, can live almost indefinitely with some of the more affordable mainstream rod bolts above, it’s rather hard to make a case for using the much more expensive and higher strength 625+ or 3.5 bolts, even if they do have higher fatigue life values.

BOTTOM LINE

So then, all we REALLY NEED, from a conservative Engineering standpoint, is to at least reach the 125% MOS target for safety and reliability, no matter how much HP is being made. And anything above that 125% is fine, but not necessary.

----------------

But, things aren’t always wine and roses, because some engines will NOT stay together and live like the well built configurations above. I've done "failed" rod bolt "Strength Analysis" on two smaller very high revving engines, after the fact, to take a look at why they failed. One blew-up catastrophically when a rod bolt broke, costing its owner 20 grand. And the other engine was found to have rod bolts stretched beyond the yield point, during a teardown for other reasons. So, its fuse had been lit, but fortunately it was caught just in the nick of time before they let go, saving its owner a ton of money and agony.

In both cases, the rod bolt "Strength Analysis" revealed that they had been built wrong, and that they were well BELOW 100% MOS, which predicts premature rod bolt failure. One had only a 67% MOS and the other had only an 86% MOS. If rod bolt "Strength Analysis" had been performed before these engines were built, during the planning stages, then all that grief and cost could have been avoided. They have since been rebuilt much stronger, with MOS values now well ABOVE that 125% safe target. And they have now been raced for some time without issue.

----------------

SUMMARY

• ARP 8740 chrome moly rod bolt - a strong affordable rod bolt, but it has only a moderate fatigue life, which makes the ARP 2000 rod bolt which is in the same general price range, a much better choice since it has twice the fatigue life.

• ARP 2000 rod bolt - considering how good its strength and fatigue life are, this rod bolt is an excellent choice for most Hotrods, Street/Strip cars, and Sportsman Drag cars.

• ARP L19 rod bolt - the strength and fatigue life increases this bolt provides over the ARP 2000 are not significant enough to overcome the concerns the L19 has with hydrogen embrittlement, stress corrosion, and the fact that it CANNOT be exposed to any moisture, including sweat and/or condensation. Don’t forget that every engine forms condensation inside, at every cold start-up. Plus, oil rises to the top of, and floats on water because of density differences, which can leave portions of the rod bolts exposed to water even after the engine is built. Therefore, it is best to avoid the L19 rod bolt altogether, especially since the ARP 2000 rod bolt already provides way more than enough strength and fatigue life than is typically required by most Hotrods, Street/Strip cars, and Sportsman Drag cars. So, there simply is no good reason to select the ARP L19 rod bolt. If you are currently running L19 bolts, I’d suggest you consider replacing them with different bolts the next time you have the motor apart.

• ARP Custom Age 625+ rod bolt - a very pricey bolt, but with its excellent strength and its impressive fatigue life, this bolt is one of the very best rod bolts on the market.

• ARP 3.5 rod bolt - this bolt has excellent strength, but its staggering cost is 43% HIGHER than the 625+ bolt, yet the 625+ bolt is superior to the 3.5 bolt in virtually every way. So, there is no good reason to select the 3.5 bolt either.

---------------

CONCLUSION and RECOMMENDATION

Of the 5 rod bolts above:

• The ARP 2000 rod bolt is an excellent value, considering how good its strength and fatigue life are. And it should be considered the rod bolt of choice for most Hotrods, Street/Strip cars, and Sportsman Drag cars, no matter how much HP they make. And this is why you most often see quality aftermarket rods come with these bolts.

• ARP Custom Age 625+ rod bolt has a price that is not for the faint of wallet, but it should be considered the rod bolt of choice for very high revving engines, road race engines, and endurance engines, which require the utmost in rod bolt strength and/or fatigue life.

540 RAT
 
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