[spankenstein]

P-51 and Jays2000ZX3 have both recently posted their compression numbers in the FI forum. They were getting 190 - 200 psi. These are engines that have been boosted for a while.

I've got a very mild NA setup and the last compression test I did was in the 160s - 170s. These were all withing Ford spec but now it seems low.

Why would my engine that wasn't subjected to the forces of boost already be making less compression? Would the cams alter these numbers?

Also, when squirting a little oil in compression in the lowest cam up about 5 psi. That shows some ring wear. Is that too much? If so waht caused it?

I did have some mild occasional detonation even while stock and since installing cams I've had to move up to 89 octane to not detonate. Has anyone else had this problem?

 

[Blue01Street]

One thing to consider. The results of a compression test are affected by atmospheric pressure. In other words the elevation will alter the absolute numbers, a check done at Sea Level will show higher nimbers than a check done at 5000 ft. It is usually more important to look at the diference between the cylinders. If they are all within tolerance and the result is in a reasonable range it should be OK.

 

[boost til' bust]

5 psi is only about 2 or 3% of a compression gain on 170psi...the ford books say no more than 20%, but 20% is pretty excessive, as long as your under 5%, that is a pretty low gain in pressure.

 

[ax0n]

Justin, if it's any consolation, that's about what my focus and my escort are pushing. I think it might be our altitude.