What is the relationship between stroke length and compression?
As far as I can tell, engines with a longer stroke tend to have more torque down low, but doesn't longer stroke = higher compression a la integra type R and S2000?

 

engine stroke does not have anything to do with the compression!! the longer stroke = more torque yes but, once again the stroke has nothing to do with the compression of an engine.

 

stroke -> rod ratio -> port volume -> cam selection -> intake ABDC / dynamic CR -> static CR.

one dictates the other in a parts integration package. The hub are the cams. The cam choice is affected by the rod ratio. The intake cam ABDC closing point dictates how much CR you need to maintain sufficient adequate cylinder pressures.

Low rod ratio engines love longer duration cams. Longer duration needs more CR. That's the link.

If you want an equation, I don't have one.

 

A b18B has a longer stroke than a B18c or C5, but less of a nominal/static compression ratio.
Seems to depend on the the volumes since the compression ratio is dependent on volumes).. volume BDC and volume TDC.


[Modified by Zygspeed, 12:35 AM 9/10/2002]

 

the smaller CR was a matter of choice by Honda and not dictated by the stroke directly. They could easily have put in different cams and a higher CR to give the b18b the proper cranking pressure.

You see this in Toda B's. When you hear that someone has to advance the intake cam 10-12 degrees with a cam, you know that the engine was overcammed. The earlier closing point on the intake valve is an attempt to recapture cranking pressure lost up the intake port from the Toda B's late ABDC intake closing point.

You either get back the cranking pressure from a larger dome height or from an extreme advance on the intake cam.

Why do you think Toda only offers 12.3:1 CR pistons for the B18C? Look at their cams.