ak

Does anyone know what a good healthy compression test psi number would be on a warm big block chev with the throttle wide open?????????????This is on A 509ci,about 10:1 compression ratio,healthy cam and good heads.

HotPursuit

consistency between the 8 cylinders would be most important. Use a leak down gauge no questions on whats right. 100% is perfect anything below is your % loss.

stevesxm

he's right. if you are locked into a compression test look for them to be 130 or 140 or so but remember, the more agressive the cam, the lower the cranking compression will be. whst s compression test will really tell you is if you haver dinged a valve or have some other meaningfull big sealing issue.

Young Performance

Its all going to depend on the camshaft. The larger the cam, the lower the cranking compression. As Keith said, you are looking for equality between the cylinders. That is more important than the actual number. I would think you should be somewhere around 175-180 psi. You need to be more concerned with the numbers being within 10 psi from highest to lowest.
Also as Keith said, a leakdown eliminates any questions. It will tell you not only what kind of shape it is in, but where the problem lies if you have one.
Eddie

I'CE

10.2 compression/moderately aggressive cam 540CI NA dyno 640HP 145 lbs cylinder test + - 5% just for a refer. guide. j

HotPursuit

Happy New Year Chalmation Brother!!!

ak

Well i am doing great then,did a compression check,warm with throttle open got 189-192 psi across the board and leak down was 13% across the board,i used new matco testers for these tests,the leakdown gauge read 5-10% was the set mark,10-40% was low mark,40-70 was the moderate mark and 70-100% was high mark,so i guess she is pretty healthy.

Griff

Pretty decent numbers. The leakdown is a little high, but its good that all cylinders are the same.