Questions and Answers

Acura Integra GS-R Compression Test Q. Hi Vincent, I have a 1995 Acura Integra GS-R with 660 miles on a newly rebuilt engine, modified with 11:1 forged pistons and chrome rings. I'm still, according to the Haynes manual, on break-in period and revved up to 7,000 a few times. The head is also newly rebuilt. I did a compression test and got 195, 185, 185 and 190 psi across the cylinders.

My friends have high mileage Integras with stock internals and have 220 average psi. Why is my high compression pistons not putting out higher numbers like my friends stock ones? I figured maybe that the rings didn't seal good or are not done sealing so I have lower compression numbers. Do I put more miles and check again later?

I'm still on break-in period and revved up to 7,000 a few times. Could driving too hard during break-in period hurt my compression? The machine shop is reputable, but I'm not sure if they did a lousy job?

Thank you,
Tommy

A. The compression ratio in that engine is 10:1. Normal is 270 psi with a minimum of 140 psi at 250 rpm and the throttle wide open. Can't compress air if it can't get into the cylinder. There is a maximum of 28 psi difference between cylinders allowed.

Your compression readings are about normal for that engine. It will go up somewhat as the rings and valves seat in so give it some time. with compression readings, the actual compression is not as important as uniformity between cylinders.

7,000 rpm while doing the break in is not good, and counter productive to what you are trying to achieve. Personally, I recommend no more than 4,000 rpm within the first 1,500 to 2,000 miles of a rebuild.

After 2,000 miles check the compression again and see where you are. If you were looking to substantially increase the compression with the new pistons and rings, you may be disappointed. Neither one will give you any real increase in compression. The chrome rings are for smoothness to allow them to ride against the cylinder walls with less friction. In and of themselves will not increase compression.

If you are looking at more compression, milling the cylinder head will increase compression by making the combustion chamber smaller. But the maximum you'll get is maybe 10.5:1