Did a compression check, is my motor shot?


Founding Member
May 3, 2002
I checked my compression on my motor recently and it read 140-145 on all cylinders except for number 8 which read 120. What should I be reading on a perfectly healthy motor. Also how much will one cylinder that low hurt my performance. By the way it is a stock shortblock thats been rebuilt about 2000km with AFR 185 heads and a comp HR284 blower cam. I guess the cam can bleed off some compression correct? The main reason Im posting this is because my car has been really down on power lately and this has to be the problem. It's been like this ever since I blew a head gasket at the track, and since that I've added another fuel pump (255 in line) and put on some new AFR 185 heads (replacing the edlebrock rpms) I've had it to the track and it only went [email protected], and before it did an [email protected], so something is really wrong here. But can the small loss of compression in that one cylinder make the car loose that much power?
sorry for the long post
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15 Year Member
Nov 29, 1999
a leak down test might offer more answers for you. how about wet compression test?

normally being within 10% is good. i think you are close enough for arguments sake. just my two cents worth.
good luck.


Founding Member
May 22, 2000
Roaring Spring,PA
I agree with the leakdown test. You can pick up the testers pretty reasonable and after you use one you'll never do another compression test. With the leakdown you can trace it to where it's losing it's seal. Many times it's valves instead of rings and with a leakdown you can hear where the air is rushing out and make a much more accurate judgement.