Interpreting compression test

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Jul 18, 2006 | 07:18 PM

75 Hot One

Thread Starter

Pro

Joined: Mar 2001

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From: Hamilton, ON, Canada

Interpreting compression test

I've got compression test results ranging from 160 psi to 175 psi with a Crane cam with 244 deg intake duration and 252 exhaust. Does this indicate a problem? Chevy shop manual suggests there's a problem if the compression is different between cylinders but doesn't give any tolerance. What is the max allowable difference between cylinders before a problem is indicated?

Jul 18, 2006 | 07:48 PM

Gordonm

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From: Forked River NJ

My motor is brand new about 50 miles on it. Mine ranges from 170 to 175 with a pretty big cam in it. Usually within 10% on a used motor is not to bad.

Jul 18, 2006 | 08:39 PM

mandm1200

Melting Slicks

Joined: Jan 2004

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From: New Cumberland PA

Quote:

Originally Posted by Gordonm

My motor is brand new about 50 miles on it. Mine ranges from 170 to 175 with a pretty big cam in it. Usually within 10% on a used motor is not to bad.

10% is the general rule. I did a compression test after about 50 miles; 195 to 205 with a mild cam.

Jul 18, 2006 | 08:46 PM

ajrothm

Le Mans Master

Joined: May 2006

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From: League City Tx

Make sure you are doing the compression test with the engine warm and the throttle/secondaries wired open. If you test with the throttle closed it will kill 15-20psi.