do camshafts affect compression????? i hear that smaller cams will give the motor more compression and big cams make the motor lose compression is that true??

 

yes. because of the overlap in the camshafts let out some of the fuel mixture while the intake and exhaust valves are open. A smaller camshaft has less overlap so it doesn't let out as much of the mixture. But this is all at low rpm. Thats why a big camsahft doesn't idle well.

 

If your talking cranking compression as in a compression gauge you are right.Bigger cams open the intake sooner and close the exhaust later,so there is less time to build cylinder pressure.This is why you want a higher compression ratio with a larger cam.With out doing this you loose low end torque from the loss of cylinder pressure.Big cams won't affect your compression ratio.
Glenn

 

Yes and no.

It will not drop the static compression (compression ratio) but it will drop the dynamic compression. As said, the duration will cause the air to flow out of the head when both valves are open, effectively losing compression while the motor is running. This is why you want to run a higher compression ratio with bigger cams.

 

Intresting. I had a set of Civic Si cams in my 12.2:1 LSVTEC, and I was cranking over almost 300psi on a compression gauge..