compression check

**jaslivers** · 03-31-2009, 10:39 AM

when i bought the z28 the guy said it had a cracked #2 piston and it was throwing codes, i took it in and there were no codes/no check engine light

well today i got a compression check done and it was a little under 20%
is that good, bad, ugly? any help would be nice

the car runs amazing with no miss/sputtering

**pajeff02** · 03-31-2009, 11:05 AM

Did you check all 8 cylinders, or just No. 2? Generally, you should check all 8 and then look for the variance between cylinders. My recollection is that they should all be within 10%-15% of one another, meaning if that your high is 140 p.s.i., your lowest shouldn't be any less than 120 p.s.i. (This is by way of example only and is not indicative of actual stock compression). You should then perform a leak down test to continue the diagnosis from there. Someone here can probably tell you what stock compression should be...

**jaslivers** · 03-31-2009, 12:02 PM

hmm we only did the one

**pajeff02** · 03-31-2009, 12:08 PM

You can also check the top of the piston for damage with a bore scope. Does it seem to make any noise or are you getting excessive blowby from the PCV?

**jaslivers** · 03-31-2009, 12:15 PM

negative, everything runs/sounds fine

**bills98ta** · 03-31-2009, 01:43 PM

Sounds like someone got a bargain !!!

**jaslivers** · 03-31-2009, 01:45 PM

haha thats what im hoping i got the car for about half of what others are going for
2001 artic white z28, m6, lid, exhaust, 62k miles

**Cutlass** · 04-01-2009, 05:42 AM

If you just did one and you got 20 %, it sounds like you did a leak down test. 20% leak down is ok, not great but ok.
Do the other cylinders for comparison and do a compression test also. post the results