I know pretty much everyone on here has at one time or another heard " Running bigger cams bleeds off compression". My question is why does it bleed off compression ? Is it the added duration that causes this to happen ? I have also read that this is a big myth. Could someone clear this common saying up ?

 

Simple version:

If you have a lot of duration, when the piston starts up on the compression stroke the exhaust valves are still open a bit, so some of the charge is pushed out, so compression bleeds out a bit. With really big cams, it is almost as if the piston is chasing the valves closed.

 

good explaination, it makes sense

 

But not as much if you have a VTEC motor. Have you ever figured out you have more cam lobes than a Chevy? Do not even try to figure ont K motors, with VTEC and adj. cam timing.

 

But does it bleed compression... or vacuum?

 

arent the two directly related?

 

Yes, but regardless of how big the cams are, the valves are still closed on the compression stroke. So youre not bleeding off compression, youre bleeding off vacuum.

 

yeah, thats what i meant. but you could say you are bleeding off compression because you are bleeding off vacuum. but im taking your words in the most literal sense