Thread: Too much crankcase pressure, novice engine builder

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Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

Leak down test is a must do.
JMHO, your compression test shows a problem.

Originally Posted by NegativeZero

Static compression ratio is 10.1:1 Results of a cylinder compression test are as follows:
cyl1 - 135 psi lower mid of 10% compared to highest
cyl2 - 130 psi very low side of 10% compared to highest
cyl3 - 139 psi upper side of 10% compared to highest
cyl4 - 132 psi borderline low side of 10% compared to highest
cyl5 - 133 psi borderline low side of 10% compared to highest
cyl6 - 137 psi mid side of 10% compared to highest
cyl7 - 125 psi below 10% compared to highest
cyl8 - 143 psi highest

Originally Posted by NegativeZero

I will get in touch with them before hand..... and see what they would like me to do and what fuel they'd want me to have in the tank.

Just my $0.02 if they tell you to have anything other than the fuel you want to run I'd be asking them why they would tune with different fuel. Just doesn't make sense to me. You'll end up with your timing too far advanced for the fuel you plan to run.

Originally Posted by 36 sedan

Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

36 sedan, not too awfully long ago you posted one of the best picture references on reading plugs I've ever seen. Is that something you might have close and could repost here. It was the best.

Originally Posted by 36 sedan

Read your plugs, they will tell you if detonation is present by specks on the porcelain (or worse melted). The plugs will also tell you your tuning.

Leak down test is a must do.
JMHO, your compression test shows a problem.

I've done a lot of reading on this and can't seem to find an exact answer, but cylinders within 15% of each other seemed to be the general consensus for acceptable.

A leak down kit has been ordered and I'm sure will give some results to consider.

Originally Posted by NegativeZero

I've done a lot of reading on this and can't seem to find an exact answer, but cylinders within 15% of each other seemed to be the general consensus for acceptable.

A leak down kit has been ordered and I'm sure will give some results to consider.

15% is a pretty wide spread. I would question anything more than 10%, especially on a new motor. Did you follow with a wet test?
Probably irrelevant, the leak down test will tell more.