Jim,
Ok, I'm going to take a stab at #8. I think the answer to your question is
really yes and no. The static compression ratio is a mathematical calculation
which takes into account different factors such as bore stroke, head chamber,
gasket thickness etc. The Dynamic compression is actually the cylinder pressure
observed during engine operation. Because gasses and fuel have momentum just
like anything else, the intake valve will stay open during the compression
stroke, and at higher RPM should actually draw in more air while even while the
piston is moving upwards on its compression stroke (I'm told by members of the
OSU formula SAE team that their engine can actually draw in a greater volume of
air than the cylinder volume at the correct engine speed). Because the intake
valve is hanging open into the compression stroke it is actually bleeding off
pressure, but if you look at what you are really doing, the calculations for
the static compression ratio are now wrong, because you have effectively
shortened the stroke of the engine during compression (in some cases by quite a
few degrees of crankshaft rotation if the engine has a very high RPM cam). So
really when you account for the shortening of the stroke dynamic (or actual
effective compression) and static compression are related, but because of
different cam grinds and timing, static compression and dynamic cylinder
pressure dont have to be directly related. ie. it is possible for me to shave
my tr6 head (to increase static compression) and change the cam to something
more aggressive (*at the same disassembly) and end up with a lower cylinder
pressure next time I do a dynamic compression test.
I'm not sure if this is what you were looking for, but I thought I would throw
it out there,
Ryan Miles
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