calculating piston pin height/compression height

[grumpyvette]

"
HEY GRUMPYVETTE?
I picked up a tall deck,Chevy big block 427, block, at a yard sale and a friend donated a set of 454 .060 pistons
Ive got several intakes for big block engines ,both oval and rectangular port, styles, whats it going to take to build a 496 stroker from these components?"

it should be rather obvious that youll need to know the exact distance the piston deck sits at TDC ,above or below the block deck surface and the valve notch recess or pop-up dome volume of the piston to do accurate quench or compression calculations
if you find the rotating assembly is more difficult to rotate than you expected, you may want to verify some clearance issues that get over looked at times,
theres also some, other potential issues,
theres a slight potential for the piston wrist pins too not rotate effortlessly in the piston pin bores ,

that may add to the difficulty in rotating the assembly in the block.
the piston rings must have vertical and back clearance in the piston ring grooves

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

Any decent, experienced machine shop can measure your cylinder heads combustion chamber,
and calculate the required clearances after measuring your heads combustion chamber, and then do the correct machine work on your piston domes,
machining the domes for adequate,spark plug,clearance,
this is a very common issue and easily resolved,

and it seldom costs much to have done.

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

Piston Ring Groove Clearance
Pistons are grooved to fit rings that seal the cylinder’s compression and allow for lubrication of the cylinder walls. Piston rings come in a set. There are two compression rings. The top ring is affected by the most cylinder compression pressures. The second compression ring reinforces the top ring. The third ring down is the oil ring. It controls lubrication between the piston and cylinder bore.

Place the new ring into the top piston groove, and then place a feeler gauge into the gap between the new ring and the upper land. Move around the pistons groove and obtain a few measurements. Compare this reading to specifications. If this reading is too much and the gap is too large, the piston must be replaced. The top ring takes the most compression. This causes the ring to slap against and wear the lands in the piston groove.

and of course the pistons must have the correct piston too bore 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
lets look at a quick example, say you want pistons for your 400sbc, you can select either 5.7" or 6" connecting rods for use in a 400 sbc, either is an improvement over the stock 5.565" connecting rods, most guys feel the 5.7" is the best choice due to the need to place the wrist pin up into the oil ring groove on pistons with the higher 6" rods required pin location and shorter piston compression height.

http://scatcrankshafts.com/#6

notice how the longer crank stroke effects the piston stroke distance in the bore, both at the lower and upper end of the cylinder
5.7" rod piston
https://www.uempistons.com/index.php?ma ... cts_id=149


6" rod piston
https://www.uempistons.com/index.php?ma ... cts_id=416
a small block has a 9" deck height, subtract 1/2 the stroke plus the rod length from that 9" to get the required pin height
most blocks actually measure between 9.00-9.023"
If you use a 5.7" rod in a 400 with its 3.75" stroke ,you need a 1.433 compression height .......because 1/2 of 3.75" stroke = 1.875" + 5.7"+1.433=9.008"
http://victorylibrary.com/mopar/rod-tech-c.htm

If you use a 6" rod in a 400 with its 3.75" stroke you need a 1.13 compression height.......because 1/2 of 3.75" stroke = 1.875" + 6"+1.13 =9.005"

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

well the first thing youll need to do is get a machine shop to check the block for cracks, verify line bore straitness, look for the deck to be strait, and check for other problems, and sonic check the bore walls to see if it can be bored to .060 over bore to fit the pistons you have, have the pistons inspected and measured, before considering their re-use. now if that was a standard bore block with a standard deck the pistons would not work,but with the taller deck height of the tall deck block youve got a shot at using those components.

the standard compression height on a 454 piston is about 1.645" compression height,the stock rod is 6.135" and with a 4" stroke crank that adds up to a 9.78 total for the standard 9.8" deck block, but theres commonly about .023 extra deck thickness if its never been milled/decked
on your taller tall deck block with its 10.2"(plus .023") deck height you have a 454 piston is about 1.645" compression height, the stroke on a 496 is increased to 4.25" so you have 2.125"= 1.645" pin height and a 10.2" deck that leaves you with a 6.430-.6.453" potential rod length, the closest standard rod is a 6.385", leaving the piston deck at .010-.033 below the deck of the block before theres a head gasket added, the next longer rod is 6.535" you can find combos that can come close to fitting

be aware that the other common BBC piston pin heights are 1.270, 1.520 and 1.765",
bbc connecting rods come in 6.135", 6.385" ,6.535", 6.700" and 6.800"
obviously theres other combos if your willing to change connecting rods or pistons

http://www.wallaceracing.com/Calc-Deck- ... length.php

I,m amazed at how often this concept gets confused, basically a piston compression height or the distance from the center of the piston pin hole, to the pistons deck height , is supposed to be very close to the block deck height MINUS the connecting rod length and 1/2 the crank stroke.
theres three variables here, stroke rod length and piston pin height, the piston pin height must be low enough to allow the ring pack , but theres some latitude in measurements, a longer stroke will require either a shorter connecting rod or a shorter compression pin height , but you can for example use a longer rod and shorter piston pin height with the original stroke to gain some rod/stroke ratio or clear larger crank counter weights.
Chevy V8 bore & stroke chart

Chevy V8 Crankshaft Journal Sizes

Here's a list of Chevy V-8 crankshaft journal sizes. All journal sizes are given in "STANDARD" sizes. Your crankshaft may have been cut down in size previously by a machine shop. Make sure your crank will work in the block you have. Blocks were made for each crank main journal size. If you are putting a "small" or "medium" journal smallblock crank into a "medium" or "large" journal smallblock block you will need crank bearing "spacers" or use special "thick" bearings available from aftermarket suppliers.

Chevy Smallblock V8 Crankshaft Journal Sizes


Gen.I, "Small Journal"
265...Mains-2.30"-Rods-2.00"
283...Mains-2.30"-Rods-2.00"
302...Mains-2.30"-Rods-2.00"
327...Mains-2.30"-Rods-2.00"



Gen.I, "Medium Journal", includes "Vortec" 305 and 350 thru '98
262...Mains-2.45"-Rods-2.10"
267...Mains-2.45"-Rods-2.10"
302...Mains-2.45"-Rods-2.10"
305...Mains-2.45"-Rods-2.10"
307...Mains-2.45"-Rods-2.10"
327...Mains-2.45"-Rods-2.10"
350...Mains-2.45"-Rods-2.10"



Gen.I, "Large Journal"
400...Mains-2.65"-rods-2.10"



Non-production Gen.I combination, using Gen.I 400 crank in Gen.I 350 block
383...400 crank, Mains cut to 2.45"-Rods-2.10"



Non-production Gen.I combination, using Gen.I 350 crank in Gen.I 400 block
377..."Spacer" or "thick" main bearings with 350 crank-Rods-2.10"



Gen.II, "Medium Journal", includes "L-99" 265, "LT-1" 350, "LT-4" 350
265...Mains-2.45"-rods-2.10"
305...Mains-2.45"-Rods-2.10"
350...Mains-2.45"-Rods-2.10"



Non-production Gen.II combination, using Gen.II 265 "L-99" crank in Gen.II 350 block
302...Mains-2.45"-Rods-2.10"



Gen.III, includes '97-2005 "LS-1" Corvette, Firebird, Camaro
345...Mains-2.558"-Rods-2.10"



Corvette "ZR-1", DOHC, "LT-5"
350...Mains-2.76"-Rods-2.10"


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

ALL production big blocks used a 6.135" length rod.
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"
477= 4.5" bore x 3.76" stroke
496 = 4.250" x 4.37" (2001 Vortec 8100, 8.1 liter)
502 = 4.466" x 4.00"
557T= 4.5 bore 4.375" stroke
572T = 4.560" x 4.375" (2003 "ZZ572" crate motors)

T = Tall Deck

ALL production big blocks used a 6.135" length rod.

read thru these links

viewtopic.php?f=53&t=3760&p=9968&hilit=clearances+skirt#p9968

viewtopic.php?f=50&t=1249

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

http://garage.grumpysperformance.com/index.php?threads/piston-suppliers.2208/#post-5942

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

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

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

http://www.enginelabs.com/engine-tech/stroker-engines-the-long-and-short-of-connecting-rod-length/

http://www.jepistons.com/PDFs/TechCorner/2006-je10.pdf

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

http://www.gtsparkplugs.com/CompRatioCalc.html

http://www.summitracing.com/expertadviceandnews/calcsandtools/compression-calculator

https://www.rbracing-rsr.com/compstaticcalc.html

http://www.diamondracing.net/tools/

 

[grumpyvette]

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

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

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

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

http://www.wallaceracing.com/dynamic-cr.php

http://garage.grumpysperformance.com/index.php?threads/piston-suppliers.2208/#post-5942

http://www.empirenet.com/pkelley2/DynamicCR.html

http://victorylibrary.com/tech/crod-c.htm

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

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

http://www.jepistons.com/TechCorner/Pis ... ology.aspx

http://www.crankshaftcoalition.com/wiki ... patibility

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

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

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.

http://www.enginebuildermag.com/201...ton-compression-height-and-crankshaft-stroke/

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

https://www.enginelabs.com/engine-tech/engine-blueprinting-how-to-check-piston-to-valve-clearance/

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

 

[Grumpy]

grumpy ?? can I get pistons ordered to exactly match my blocks existing deck height if its currently correctly machined flat and parallel to the crank center line ?
, What if that deck height is lets say .022 above the nominal 9.8" on my big block 454 or lets say, .020 higher on my 350 SBC block that I want to convert into a 383 rather than having the block deck height milled down

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



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

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.
yes most piston manufacturers will be only too happy to change the piston pin height on custom ordered pistons for a minimal fee of course

http://www.venolia.com/technical.html

http://www.wiseco.com/Catalogs/Automotive/CustomOrderAuto.pdf

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

https://fs18.formsite.com/flatland/form3/index.html

https://www.supertechperformance.com/custom-pistons

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

the upper closed chamber head is bath tube shaped to provide dual opposed quench areas that squish against the piston deck,
forcing the fuel air mix toward the central cylinder bore, the lower open chamber head combustion chamber was found to un-shroud the valves,\
thus increasing the cylinder fill efficiency especially at upper rpms.
the dome higher compression ratio pistons for both combustion chambers are similar in shape to the combustion chambers they are designed too be used with.
the closed chamber piston can be used with the larger open chamber combustion chamber , but its reduced volume results in less effective compression and the dome,
of the closed chamber dome is marginally restrictive to the flame front propagation.

no, if you have any engine and want too find the rure compression you need to deal in verified fact, not assume what the manufacturers suggest is always correct.
you just cc the heads, combustion chamber volume, place the piston 1" down the bore and seal the rings gap around the pistons,
above the rings with moly grease or Vaseline and measure that volume and calculate what a bore diameter cylinder 1" tall would
contain, minus the volume you,ve measured, the piston dome took up.then calculate the true compression.

read related linked info

http://garage.grumpysperformance.co...n-chamber-or-piston-dome-or-port-volume.2077/

http://garage.grumpysperformance.com/index.php?threads/ccing-my-heads.14187/#post-71989

http://garage.grumpysperformance.co...ng-combustion-chambers.2630/page-3#post-77963

http://garage.grumpysperformance.com/index.php?threads/calculate-compression.9162/#post-32706

http://garage.grumpysperformance.com/index.php?threads/can-you-plan-for-quench.11298/

http://garage.grumpysperformance.co...on-picking-a-shop-to-do-work.5053/#post-28837

http://garage.grumpysperformance.co...e-and-piston-dome-dish-volume.3061/#post-8090

http://garage.grumpysperformance.co...od-rod-length-too-stroke-info.510/#post-12288

YOULL OBVIOUSLY NEED TO DO SOME MATH AND CAREFULLY PLAN ANY COMBO,EXAMPLE

Grumpy? I'm doing a rebuild on my low mileage 383. My question is if 10.3 compression is too much for xe 268 comp cam which I have already? The motor has kb 197 dish pistons, .025 down, .015 shim head gasket, TFS 195 heads with 64 cc chambers. Edl RPM airgap, Demon 750 dp and 1 5/8 headers. It's going into a 83 chevy wagon with 200r4, 2200 stall and 373 rear gears. Do you think this combo will work with 93 octane, or do i need to lower the compression ?

ok lets look at the math a bit,
youll generally be fine with 93 octane fuel and using aluminum cylinder heads if you keep the engine coolant temps under about 215F
and the DYNAMIC compression under about 8.2:1 ,
dynamic compression is based on where in the crank rotation the valves both close as the piston can,t compress anything until the valves seal.
the charts based on iron cylinder heads and yours are aluminum which will generally allow about a 1/2 point in dynamic compression higher without issues.
your pistons are listed as having a 12cc dish volume, and being .025 down the bore adds about 5.6 cc more
https://www.summitracing.com/parts/UEM-KB197-030/
thus you have about 10.25:1 static compression

the math shows your dynamic compression will be near 9.5:1 which is a bit too high for reliability without an additional octane booster

if we look at your cam we see it is listed as having 224 duration on a 110 lsa


http://www.compcams.com/v002/Pages/388/XE268H-10.aspx

if we look at this chart we see that your intake valve closed at about 38 degrees after bdc.

you might want to read thru these link's carefully
http://victorylibrary.com/mopar/cam-tech-c.htm

http://members.uia.net/pkelley2/DynamicCR.html

http://www.wallaceracing.com/dynamic-cr.php

http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

OK, first fact! the piston can,t compress anything being trapped in the cylinder by the piston compressing it as it raises,until both valves seat & seal

http://garage.grumpysperformance.com/index.php?threads/dynamic-vs-static-compression.727/

http://garage.grumpysperformance.co...-calculators-and-basic-math.10705/#post-46768

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581

http://garage.grumpysperformance.com/index.php?threads/crowers-valve-timing-charts.4299/

http://garage.grumpysperformance.com/index.php?threads/how-to-read-a-cam-spec-card.1477/#post-3329

heres some calculators you might use

http://www.angelfire.com/fl/procrastination/mo tor....

http://www.thirdgen.org/calculations

http://www.bgsoflex.com/holley.html

http://www.ford-trucks.com/calculators/index.php

http://hotrodworks.net/hotrodmath/hotrodmath .html

http://www.wallaceracing.com/dynamic-cr.php

http://www.dsm.org/tools/calchp.htm

http://www.wahiduddin.net/calc/calc_hp_dp.htm

http://users.erols.com/srweiss/calccr.htm

http://users.erols.com/srweiss/index.html#jcalc

http://wahiduddin.net/calc/calc_da.htm

http://www.bob2000.com/carb.htm

http://www.ondoperformance.com/page2.html

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

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

http://www.engr.colostate.edu/~allan...ngth/pipe.h...

http://purplesagetradingp ost.com/sumner/bvillecar/...

http://www.rceng.com/technical.aspx

gear spread sheet that comes in handy THANKS TO 1FATGMC

http://purplesagetradingp ost.com/sumner/bvillecar/...

HERES OTHER INFO LINKS

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

http://users.erols.com/srweiss/calcmph.htm

http://users.erols.com/srweiss/calcrpm.htm

http://users.erols.com/srweiss/calcrgr.htm

http://users.erols.com/srweiss/transc.htm#tabtop

http://users.erols.com/srweiss/transc.htm#Auto

http://www.pipeflowcalculations.com/airflow/index....

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

http://www.uucmotorwerks.com/html_pr...torquemyth....

http://tom.marshall.tripod.com/exhaust.html

http://www.engr.colostate.edu/~allan...a/effarea.h...

http://www.engr.colostate.edu/~allan...ngth/pipe.h...

http://www.pontiacracing.net/js_header_length1.htm

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

http://auto.howstuffworks.com/question172.htm

http://www.auto-ware.com/software/eap/eap.htm

a few resources to allow you to calculate the ideal results
http://www.tmossporting.com/tabid/1805/Default.asp...

heres some differant calculators

http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

http://www.smokemup.com/auto_math/compression _rati...

http://not2fast.wryday.com/turbo/com...pressure.sh...
average the results

- Piston Motion Basics -
Travel, Velocity, Acceleration, Vibration
The crankshaft, connecting rods, wristpins and pistons in an engine comprise the mechanism which captures a portion of the energy released by combustion and converts that energy into useful rotary motion which has the ability to do work. This page describes the characteristics of the reciprocating motion which the crankshaft and connecting rod assembly imparts to the pistons.

A crankshaft contains two or more centrally-located coaxial cylindrical ("main") journals and one or more offset cylindrical crankpin ("rod") journals. The V8 crankshaft pictured in Figure 1 has five main journals and four rod journals.

Figure 1

The crankshaft main journals rotate in a set of supporting bearings ("main bearings"), causing the offset rod journals to rotate in a circular path around the main journal centers, the diameter of which is twice the offset of the rod journals. The diameter of that path is the engine "stroke", which is the distance the piston moves from one end to the other end of its cylinder. The big ends of the connecting rods ("conrods") contain bearings ("rod bearings") which ride on the offset rod journals. ( For details on the operation of crankshaft bearings, Click Here; For details on crankshaft design and implementation, Click Here )

The small end of the conrod is attached to the piston by means of a floating cylindrical pin ("wristpin", or in British, "gudgeon pin"). The rotation of the big end of the conrod on the rod journal causes the small end, which is constrained by the piston to be coincident with the cylinder axis, to move the piston up and down the cylinder axis.

Figure 2: TDC

The following description explains the not-so-obvious characteristics of the motion which the crankshaft / conrod mechanism imparts to the piston.

Figure 2 shows a sectional end-view of a Crankshaft, Connecting rod and Piston (CCP) mechanism when the piston is at the furthest extent of its upward (away from the crankshaft) travel, which is known as the top dead center(TDC) position (even in upside-down and horizontal engines).

The furthest extent of the piston's downward (toward the crankshaft) travel is known as the bottom dead center(BDC) position.

In the CCP mechanism shown, the crankshaft has a 4.000 inch stroke and the center-to-center length of the conrod is 6.100 inches. The rod to stroke ratio (R / S) is the center-to-center length of the conrod divided by the stroke. In this example, the R/S is 6.100 / 4.000 = 1.525.

This ratio is important because it has a large influence on piston motion asymmetry (explained below), and on the resulting vibration and balance characteristics, as well as certain performance characteristics.

For purposes of this discussion, the extended centerline of the cylinder bore intersects the center of the crankshaft main bearing, and the wristpin is coincident with the cylinder centerline (defined as zero wristpin offset). Although the following descriptions apply strictly to configurations with zero wristpin offset, the general observations apply to nonzero offset configurations as well.

Figure 3: 90° After TDC

It is important to understand that the motion of the piston within 90° before and after TDC is not symmetric with the motion 90° before and after BDC. The rotation of the crankshaft when the crankpin is within 90° of TDC moves the piston substantially more than half the stroke value. Conversely, the rotation of the crankshaft when the crankpin is within 90° of BDC moves the piston substantially less than half the stroke value. This asymmetry of motion is important because it is the source of several interesting properties relating to the operation, performance and longevity of a piston engine.

Figure 3 shows the subject CCP with the crankpin rotated 90° past TDC. Note that the piston has moved over 58% of its total stroke (2.337 inches). That is because in addition to the 2.000" (half-stroke) downward motion of the crankpin (motion projected onto the vertical plane), the crankpin has also moved horizontally outward by 2.000", putting the conrod at an angle with the vertical plane.

The cosine effect of that conrod angle functionally shortens the projected length of the conrod in the vertical plane by 0.337", from 6.100" to the 5.763" shown in the picture. This dynamic "shortening" of the conrod has the effect of adding 0.337" to the 2.000" of downward motion imparted by the crankpin rotation, as illustrated by the two vertical blue lines in Figure 3.

Figure 4: 180° After TDC

Now, since the piston has already moved about 58% of the stroke during the first 90° of crank rotation, it stands to reason that during the next 90° of crank rotation (to BDC) the piston will only have to travel the remaining 42% of the stroke to reach BDC, as shown in Figure 4.

The reason is that as the crank rotates toward BDC, the crankpin also moves horizontally back toward the center of the cylinder and "restores" the effective length of the rod. That cosine-effect "lengthening" of the conrod opposes the downward movement of the piston, subtracting 0.337 from the half-stroke of vertical motion produced from 90° to BDC. That effect is illustrated by the lower two vertical blue lines in Figure 4.

Clearly then, when the crankshaft is in any position other than TDC or BDC, the axis of the connecting rod is no longer parallel to the centerline of the cylinder (the line along which the piston, wristpin and small end of the rod are constrained to move). Therefore, the "effective length" of the conrod at any point other than TDC or BDC is the actual conrod center-to-center length multiplied by the cosine of the angle between the rod and the cylinder centerline. It is clear that the dynamic change in the conrod effective length adds to and subtracts from the purely sinusoidal motion caused by crankpin rotation.

Figure 5: Half-Stroke







Figure 5 shows that, with the R / S in this CCP example (1.525), the half-stroke position of the piston occurs at about 81° crank rotation after TDC. The rapid change in volume of the combustion chamber after the TDC position has some interesting ramifications with respect to the P-V diagram and thermal efficiency (discussed on a different page).





(Note: If you believe that installing longer connecting rods will increase an engine's stroke, there's no need for you to go any further on this page, or on this entire site, for that matter.)







[paste:font size="4"]Velocity and Acceleration page, or any basic calculus text, such as ref-1:2:39) .)

Figure 6: Maximum Velocity

For simplicity of explanation, I have chosen to use crank rotation as the reference for these graphs. Typically, one is interested in the rate of change of piston position with respect to time, which would yield velocity in inches or feet per second, and the value would depend on the rotation speed of the crankshaft.

It is obvious that, as the piston moves from TDC to BDC and back, the velocity is constantly changing, and that the piston velocity is zero at TDC and BDC. The value and location of the maximum velocity with respect to crank rotation (the maximum slope of the position curve) are strongly influenced by the R / S ratio.

Figure 6 shows the location of the point of maximum piston velocity, in crankshaft degrees before and after TDC, for the configuration used in this example (4-inch stroke, 6.100" rod length, R / S = 1.525). At that position (73.9° before and after TDC), the piston has traveled only 43.9% (1.756") of the total stroke (4.000"). For this configuration (R / S = 1.525), at 4000 RPM, the peak piston velocity is 4390 feet per minute. For a longer stroke with the same R / S, the location of peak piston velocity would be the same, but the actual value of that velocity would be higher (at the same RPM, of course).

Figure 7 shows graphs of piston position and of instantaneous velocity as a function of crankshaft rotation. The blue line ("position") shows piston location (as a % of stroke) at any point during one rotation of the crankshaft. The blue line is artificially oriented so as to show position in an intuitive sense (top, bottom), therefore the "-" signs shoud be ignored with respect to position. The green velocity line shows the relative speed of the piston (as a % of maximum) at any point. Velocity with a "plus" sign is motion TOWARD the crankshaft; velocity with a "minus" sign is motion AWAY from the crankshaft.

Note again that at TDC and again at BDC, the piston velocity is zero, because the piston reverses direction at those points, and in order to change direction, the piston must be stopped at some point.

Note also that the position plot (blue) shows that, for this R / S ratio ( 1.525 ), the 50% stroke positions occur at approximately 81° before and after TDC (as illustrated in Figure 5 above). The velocity plot (green line) shows the maximum piston velocities occur at about 74° before and after TDC (as illustrated in Figure 6 above). The velocity line also shows that the piston velocity at any rotation point from TDC up to the maximum velocity is greater than at the same number of degrees before BDC. For example, compare the velocity at 30° after TDC (62%) with the velocity at 30° before BDC (34%).

Figure 7

The profile of the velocity curve, and therefore the location of the maximum velocity, are both influenced by the R / S ratio. As the rod gets shorter with respect to stroke (a smaller R / S ratio), two interesting things happen which can have important effects on cylinder filling: (1) the point of maximum piston velocity moves closer to TDC, and (2) the piston moves away from TDC faster, creating a stronger intake pulse. The location of maximum piston velocity influences the design of camshaft lobe profiles (especially intake) in order to optimize the intake event in a particular speed range, and can have an influence on the intake characteristics with regard to the strength and shaping of the intake pulse for ram tuning.

[paste:font size="4"]Velocity and Accelerationfor a more thorough explanation.)

It is clear from Figure 7 that the piston velocity is constantly varying with respect to a constant change in angular crankshaft position (rotation). Therefore, In order to move from the zero-velocity point (TDC) to the maximum velocity point, the piston must be subjected to a large acceleration function which varies with the angular rotation of the crankshaft.

Figure 8 shows the acceleration, velocity and position plots for the example CCP under discussion. (All numeric values presented are for the 1.525 R / S in this example.)

Figure 8

The maximum positive value of acceleration (100%) occurs at TDC. Between TDC and maximum piston velocitty (74° in this case), acceleration is positive but decreasing toward zero (the piston velocity is still increasing but less rapidly). At maximum piston velocity (74° at this R / S ), the piston stops speeding up and begins to slow down. At that point, the acceleration changes direction (from a "plus" number to a "minus" number), and in so doing, momentarily passes through zero.

At this R / S, the maximum negative acceleration does not occur at BDC, but about 40° either side of BDC. The value of this maximum negative acceleration is only about 53% of the maximum positive acceleration seen at TDC. The acceleration at BDC is only 49% of the TDC maximum. The acceleration from max piston velocity (74°) to BDC is negative, and that acceleration is slowing the piston to zero velocity. Therefore, it might be (incorrectly) called deceleration. However, that same negative acceleration is applied to the piston after BDC and is causing its velocity to increase.

The zero acceleration point occurs (by definition) at the point of maximum piston velocity (74° B/A TDC), where velocity is reversing direction, but the rate of change of velocity (the slope of the curve) is zero.

The somewhat odd shape at the bottom of the total piston acceleration (magenta) curve is the result of the fact that the total piston acceleration is the sum of several orders of acceleration, the first two being the most significant. The two major orders which combine to produce this total acceleration profile are important because they can produce significant vibration challenges to the engine designer (covered in Crankshafts).

Figure 8 shows the same total piston acceleration curve (magenta line) shown in Figure 7, along with the two significant orders of piston accelerations which combine to produce that curve. The total piston acceleration curve (magenta) is the sum of the two separate accelerationorders: primary (blue) and secondary (green).

Figure 8

As explained in Piston Motion above, the piston motion in the first 90° of rotation consists of the sum of the effect of the half-stroke motion of the crankpin projected onto the vertical plane (2.000") and the effect of the apparent 0.337" "shortening" of the rod length projected onto the vertical plane. The second 90° of rotation also produces a half-stroke motion in the vertical plane, but the cosine-effect lengthening of the conrod in the vertical plane produces 0.337" motion which subtracts from the half-stroke.

The primary acceleration (blue line) is the result of the piston motion produced by the component of crankpin movement projected onto the vertical plane. This curve is a sinusoid which repeats once per revolution of the crankshaft (first order) and comprises the majority of the acceleration. Note that the primary acceleration curve crosses zero at the 90° rotation points and peaks at TDC and BDC.

The secondary acceleration (green line) is the result of the additional piston motion caused by the cosine-effect dynamic length-change of the conrod. This motion adds to the piston movement between TDC and the max velocity point and subtracts from the piston motion between the max velocity point and BDC. This curve is also sinusoidal and repeats twice per crankshaft rotation (second order) and crosses zero at the 45°, 135°, 225° and 315° rotation points. The total piston acceleration at any point is the sum of the values of the primary and secondary acceleration curves.

Contemporary piston engines tend to have R / S ratios in an approximate range of 1.5 to 2.0. Note that a rod / stroke ratio less than 1.3 is, for practical applications, not possible due to physical constraints such as the need for piston rings and a wristpin, sufficient piston skirt length, and the inconvenience of having the piston contact the crankshaft counterweight, not to mention the excessive side load such a small ratio would produce.

Here are two practical examples comparing the effects of R / S on acceleration and velocity (illustrated in Figure 9below). In a Lycoming IO-360 (and IO-540) the rod length is 6.75" and the stroke is 4.375", for a ratio of 1.543, close to the low end of the spectrum in contemporary design. At the other end of that spectrum, the connecting rod on a typical (circa 2007) 2.4-liter Formula-1 V8 engine is about 4.010" long, what your average race-engine mechanic would call a "very short rod". However, the stroke in the F1 engine is in the vicinity of 1.566", which produces a very large R / S ratio of 2.56.

Figure 9

The graph in Figure 9 clearly shows the effect of large and small R / S ratios. It is quite clear that the engine with the very small R / S ratio of 1.543 (the "long" 6.75 inch conrod, the blue velocity and acceleration curves) has a substantially higher peak acceleration (10%), a higher secondary acceleration, a higher (3%) peak velocity, an earlier (5 crank degrees) velocity peak location, and the very distinct acceleration reversal around BDC, confirming the substantial secondary vibration component.

Compare that to the large 2.56 R / S ratio (the "short" 4.01 inch conrod) magenta curves, showing a substantially lower (10%) peak acceleration, a lower secondary acceleration, a later and slightly lower (3%) peak velocity, and a total acceleration curve which is closer to symmetric, confirming the substantially-reduced secondary vibration component. Figure 9 also clearly demonstrates the absurdity of discussing conrod length as an absolute.

Figure 10 is a chart listing the main effects of R / S ratios varying from 1.40 to 2.55. I chose R / S = 2.0 to be the reference point for these comparisons of Vmax %, PPA max-positive %, and PPA max-negative % because that ratio is the lowest at which the maximum negative acceleration occurs at BDC. Notice that at R / S ratios above 2.00, the acceleration curve becomes more symmetric, but the peak velocity does not change much at all.

 

[Grumpy]

Are the edlebrock 100cc heads to big for a 402 BBC .040 over
Concerned about Intake runner size 290
Here's my combo
750 hp Holley carb
Edlebrock performer rpm intake
Right now 4290 factory heads 2.06/1.72 oval
Kb 160 .040 pistons 9.7 compression
Edlebrock cam 5.60/5.73
Hooker super comp headersl
Exhaust 2.5 with h pipe
Fluid harmionic balancer

Thank you for any imput

no! from experience on several 396-402 engines I can assure you the edelbrock heads, DO tend to increase power, as the heads flow slightly better , than the OEM heads unless those OEM heads are ported.
that being stated Id look at the cost of the heads and look at a 4" stroke 454 crank and new pistons to compare. the cost vs benefits, its generally a good idea to step back and use a legal pad and calculator to get a good grip on cost vs potential benefits before jumping into any engine build.
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 theres 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.

Details for 3964290

Casting Number 3964290
Added to Site 2010-12-25 18:03:33 (2280 days ago)
Manufacturer Chevrolet
Category Cylinder Heads
Type Big Block V8
Date 1969-1970
Notes oval port, closed chamber, 396, 402, 427, 454, 101cc chambers
http://garage.grumpysperformance.co...ng-piston-pin-height-compression-height.5064/

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

if you change to much cheaper and much stronger 5.7" connecting rods the less common compression height pistons are not an issue
youll have dozens of choices in a 4.125-4.165 bore diam. with a 5.7" rod
keep in mind the old O.E.M. rods have already been through millions of stress cycles and they are a weak design
resizing, , refurbishing the original 400 connecting rods, and replacing
just the connecting rod bolts will cost far more than the SCAT 5.7" aftermarket rods that are at least TWICE as strong
.

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

https://www.speedwaymotors.com/KB-Claimer-Chevy-400-Hypereutectic-Pistons-Flat-Top-57-Rod,33222.html
http://www.enginebuildermag.com/2018/02/performance-pistons-101/

5.565 rods
http://www.herbertcams.com/espcrs5565b-3d-sb-chevy-5-565-4340-forged-h-beam-rods/

https://www.stevemorrisengines.com/...cks/sbc/sbc-4340-forged-h-beam-rods-5565.html


5.7" rods
https://www.speedwaymotors.com/Smal...el-I-Beam-Rods-5-7-Inch-Bushed-Pin,29376.html

https://www.speedwaymotors.com/Scat...340-I-Beam-Rods-5-7-Inch-Bushed-Pin,6608.html


piston for 5.7 rod
https://www.summitracing.com/parts/slp-h615cp


piston for 5.565 rods
https://www.summitracing.com/parts/slp-h400cp
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
reading the links and sub-links below will be
WELL WORTH THE TIME AND EFFORT
http://garage.grumpysperformance.com/index.php?threads/basic-396-bbc-build-video.13157/

http://garage.grumpysperformance.com/index.php?threads/1965-66-396-engines.10360/

http://garage.grumpysperformance.co...402-bbc-with-a-4-454-crank-or-even-4-25.2165/

http://garage.grumpysperformance.co...g-block-head-comparison.319/page-2#post-61658

http://garage.grumpysperformance.com/index.php?threads/matching-parts-and-a-logical-plan.7722/

http://garage.grumpysperformance.com/index.php?threads/what-to-look-for-in-a-good-engine-combo.9930/

http://www.diamondracing.net/

http://garage.grumpysperformance.com/index.php?threads/454-bbc-on-the-cheap-well-to-start.11739/

http://garage.grumpysperformance.co...le-that-don-t-use-resources.12125/#post-58374

http://garage.grumpysperformance.co...gine-to-match-the-cam-specs.11764/#post-55651

http://garage.grumpysperformance.co...ing-parts-and-a-logical-plan.7722/#post-68651

http://garage.grumpysperformance.com/index.php?threads/a-mid-range-454-bbc-build.8215/

http://garage.grumpysperformance.com/index.php?threads/cheaper-454-chevy-build.4620/

http://www.maliburacing.com/patrick_budd_article.htm