What should i be seeing for a comp check on my LT1? also would a compr check detect a leaking exhaust valve?
I have, what sounds like gas burnig in the exhaust when you let off the gas.. like a rumbling back fire.. buddy thought could be a valve.. SInce i did put 1.6:1 roller rockers on.. i may not have tightened one or more rockers correctly.. however you don't really hear and ticking.. its a 96 motor.. and 94 pcm.. and its 2bolt out of a firebird. Al heads.

thanks..

 

The comp should be somewhere in the 140-190 depending on the condition of the engine. More importantly the numbers should all be within about a 15-20 psi of eachother. A leaking exhast valve might show up in the test but a cylinder leak down test will be a surefire way to find out whether you have one or not.

 

Dank is right. A cylinder leakage test is a lot more reliable. A cranking compression test is so subject to cam design and valve timing that quoting a hard-and-fast good/bad number is impossible. I'm certain the cranking compression on my '94 is quite a bit lower than it was before the modifications. I'm equally certain that the engine is in a lot better condition and produces significantly more power than before.

 

excuse the ignorance.. but how do u do a leak down test?

 

You need a cylinder leak down tester and a compressor. You use the same adapter as a compression tester and fill the cylinder with compressed air with the cylinder at tdc compression. The gauge tells you a percentage of leakdown. Then you listen for air escaping.

Oil fill cap-Ring leakage
Throttle body-Intake valve
Tailpipe-Exhaust valve
Bubles in radiator-Head gasket (Not best method for finding bad head gasket thou)