rod to stroke ratio chart

[3.4Z24]

stroke......rod length.......piston pin height.......R/S ratio.....displacement

_3.000______6.00__________1.314___________2:1_____ ___3.08

_3.125______6.00__________1.251_________1.92:1____ ___3.21

_3.250______5.85__________1.339__________1.8:1____ ___3.34

_3.310______5.85__________1.309_________1.77:1____ ___3.40

_3.375______5.85__________1.277_________1.73:1____ ___3.47

_3.500______5.70__________1.364_________1.63:1____ ___3.596

_3.625______5.70__________1.301_________1.57:1____ ___3.72

_3.750______5.70__________1.239_________1.52:1____ ___3.85



cyl. bore: 3.650(0.030 OS)
min. pin height: 1.25 (to allow for ring pack)
deck height: 8.814(.005 under)

[3.4Z24]

checking out the Chevy Power manual i see these V6's can use modified small journal small block chevy V8 connecting rods. being wary of how rod to stroke ratio can affect compression ratio tolerance, i threw together a chart relating different components based on available rod lengths and custom crank stroke and piston pin height combinations.


i know 60 deg V6's won't clear strokes as far as i went, it's interesting to see the possible combinations and displacements.

i like the R/S ratio of the stock stroke(3.31) and 5.85 rods. mainly because it eliminates the need to have a custom crank made($$$).

i figure if we want forged pistons and their only available custom made, why not move the pin height up and use a longer rod? compression ratio could be increased or more boost allowed with the same grade fuel and spark curve. and heavy duty V8 rods are readily available in the aftermarket.

the only drawback is the use of the factory nodular iron crankshaft, although they are a fairly strong piece with 'deep rolled fillets on all six crankpins and the center main bearing journals.' anyhow, i've never heard of one breaking under pressure. guess i'll find out.

[brian89gp]

I believe it was talked about and in order to use 6" rods the wrist pin would have to intersect the oil ring. It may be possible if you use floating pins with snaprings.

[SappySE107]

The stock RS ratio is nearly perfect according to Larry Widmer from www.theoldone.com. 1.75:1 is the optimal ratio for side loading, piston speed for higher RPM, and quench time. That is, to the best of my memory, its been a while. I know that is the ratio he recommends anyway.

The other person people follow insists that over 2:1 ratio is perfect...but I believe larry's reasoning for the 1.75.

[Streetrodder83]

The other guy is John Lingenfelter, he came up with the 2:1, back in the day when he worked for Banks. His reasoning is less rod angularity between the crank and the big end of the rod, because of this it creates less side loading on the piston. By going longer it also allows the piston to dwell slightly longer at TDC, allowing combustion chamber pressures to become higher. This isn't anything that I would be over concerned about anyway, this is one of those things once you maxed out on power, you go looking for anything to gain you a tenth more. Plus moving the wrist pin up to close to the face of the piston, weakens it. I have seen a couple SBC where the long rods were used and cheap claimer pistons were used and they cracked right above the wrist pin. Your money would be better spent in other aspects of adding performance, than trying to increase rod length. Anything running on the street 1.75 is fine, God help you if you have a Ford 302 I think that R/S Ratio is something like 1.2. Either way it's crappy just like their cars, and trucks. Oh, by the way I don't care which one's right. Both have their theories, I've done no testing to prove one way or the other. Either way if your up anywhere between those two you doing pretty well.

[Anonymous]

How about roughly 2.2:1?

http://www.60degreev6.com/phpBB2/viewtopic.php?t=490