jchrm80

iTrader: (1)

I have an 81.5 gsr block with b16 head. Cp 9.0:1 pistons. Just wondering if there was a spec for what compression numbers should be or if you all could give me an average? Just checked mine and they are all about 140, but i have nothing to compare that to. Those numbers are with no oil added and the engine was about 30*f haha.

HiProfile

If they are all w/in 5% of each other (137-143psi), then they are all okay. You have a better chance at winning your local "pick 4" lottery than getting 4 cylinders dying with the exact same psi readings. The important thing is consistency. Make sure you treated each cylinder the same - WOT while cranking same number of times. I usually let it pump the gauge 3 times with all 4 plugs out & WOT.

If you're looking to get the actual compression ratio, you'll have to do it another way. The error involved with an assembled motor will be terrible, so tearing it down & "CCing" the combustion chaimbers and tdc cylinders is about the only accurate way.

Mikey3000

your motor should also be warm so the "sealing surfaces" are at their operating temp sizes, e.g. rings, valves, etc.

jchrm80

iTrader: (1)

yeah i knew that much but I was just trying to get an estimate to make sure they were all about even. I'll do a hot compression check and compare the numbers. thanks for the input.

Spoolin18

As long as they are all within 5% of each other it is fine. I run a 84.5mm GSR with the same compression ratio and all of mine are around 140psi as well.