- Sep 28, 2011
Oh, okay, that all makes sense, thank you for explaining that to me, I'm still learning. I will have to compare the two jugs the next time I have them off.Pipes don't change compression, well at least not substantially any more than a reed might. Both are beneficial in aiding a denser charge, but the effect on compression is negligible. The reed will increase case pressure, and the pipe will help in reducing it through scavenging.
Case pressure and compression ratio of the chamber are two different things.Case pressure has a minimal effect on combustion chamber pressure, and chamber pressure has no effect on case pressure in normal operating conditions. Like I said the probable reason for the diff. in comp.of the two engines with same head volume and squish gap is differences it exhaust port window heights in the cylinder. If the window is higher the compression begins later in the stroke thus the volume being compressed becomes lesser. The combustion period becomes shorter, and the blowdown period becomes longer allowing more time for exhaust gasses to escape before the transfers open to introduce the new charge.