Bore vs. Stroke (the scientific debate)

[Steve D.]

Rod lenght does have more affect on the motor than just friction- I just don't know how much of it actually transfers to HP.  The big 3 reasons for rod length I see are:

1-long rod = more piston dwell at TDC (whatever that does...)
2-long rod = lower piston accelleration (lessens chance of ripping the pin boss out)
2-short rod = higher piston accelleration (could help draw intake charge in at lower rpm)
3-short rod = narrower motor/shorter deck block (really only an issue in vw streetcars)

[Jon]

Rod lenght does have more affect on the motor than just friction- I just don't know how much of it actually transfers to HP.  The big 3 reasons for rod length I see are:

1-long rod = more piston dwell at TDC (whatever that does...)
2-long rod = lower piston accelleration (lessens chance of ripping the pin boss out)
2-short rod = higher piston accelleration (could help draw intake charge in at lower rpm)
3-short rod = narrower motor/shorter deck block (really only an issue in vw streetcars)

You are right, but it may be a give and take deal, you may gain something but its lost in something else. Not considering the wear and lifespan of the engine.

[SOB/RFH]

I do not agree on the wear and lifespan thing about short rod/long stroke. I have run my engine with a 1.68:1 ratio for 15 years with no problems at all. I have built a few 1.66:1 motors too and they live like happy puppets. So what about the Chevy small blocks, preatty common but with a sturdy engine case, but a low ratio would affect lifespan of the pistons art least and all I know is that they work like champs with a 1.63 ratio. The Porsche rod and 84 Okrassa crank was a good combo way back "when sex was safe and racing dangerous2......so what has happend over the years (yeah I know racing is safe now and sex is unsafe). We can now cram more HP at lower rpms due to better heads and camprofiles but does that meen the longivty of a common short rod motor does not live up to that or what! Give your motor a chance to live with a big bottomend due to as mouch bore and stroke you dare, short rods and short duration cams with a lift like there is no tomorrow but keep the revvs down. Dont rev that motor to the moon but keep compression up to the absolute limit. Let's get down to earth with combos that make low rpm power and live and spend our money and time on the best springs that money can buy. The problem of today is the springs, not the rod ratio!!!