Allan4

Am I correct is saying that the tolerence range for a BBC (454) compression test is between about 145-165psi?? I need to check the compression on two motors tonight. Also, should I go off the first reading (first engine crank) or wait till pressure builds?? I've heard both ways, not sure which to go by. Thanks, Allan

Gary Anderson

I've always done it:
Warm engine
Ignition disconnected
Choke + throttle open
Charged battery
Crank til it's stable on the guage
Gary

Allan4

Okay cool, I am right on the psi's?? Thanks

Gary Anderson

Actual psi may vary depending on cam, valves, exhaust, etc. But yeah, that's about right. Just be sure the readings are within a 5-10% range (Hi vs. low cylinder reading).
Gary

Allan4

That's what I thought, thanks man, much obliged........Allan

Vinny P

If you are doing a compression test, you have to be aware of the first hit of compression. Watch the guage, you don't want that first hit to be too low. If it is low and builds up while cranking, it probably means that there is leakage in that cylinder. This is why I prefer a leak down guage. It takes all the guess work and wondering out of the equation.

GO4BROKE

Use both. The first jump is a good indicator of ring condition. I usually crank 6 revs each cylinder. Just do them all the same, its the comparison between cylinders you will pay most attention to.

Allan4

Thanks for the info guys, we postponed the test, may try in a few days. Thanks again, Allan.