Your compression #'s

[turborebel]

What are some of your compression tests showing you? I have 9:1 pistons with compression
test showing 162, 162, 162, 165. The engine has just over 3000miles on it. When it was first put together and only had 5 or 10 miles on it, it had between 185 and 195psi compression. These test were all done with the motor hot. Just wondering what other cars were doing.

 

[Savage Talon]

190 to 195 dead cold.

 

[matt98eclipse]

To me that seems a bit lower then average for 9:1. Did you make sure throttle was all the way open and your MPI fuse was pulled?

 

[turborebel]

Yes, I pulled the fuse and had the throttle open. I've done the test many times and it seems low for 9:1 pistons to me also. I think it should be closer to 200psi like it was when I first started the newly rebuilt engine. Luckily, the car is still very fast. It still would be nice
to have those 30psi back and too know how I lost them, but that is not why I started this thread. How are your cars doing? What compression ratio pistons do you have and what
are your compression tests showing. What were they at first, how have they changed over time? Thanks.

 

[1gDSM4g63]

I have 9:1 pistons too and with 150-160 is fine.

 

[aero_sallee]

172-175
A stock 2g 8.5:1 7 bolt that i got for $50 with a badly lunched valves and unknown mileage. Swapped heads with a 150k mile stock 2g head and came up with those #. Stock cams, hot motor. Approximately 1200ft altitude.



Are you testing this with stock cams? Keep in mind that cam changes will effect compression test results.

 

[silver bullit]

I had 185-195

 

[Turbo Monk3y]

Yes, I pulled the fuse and had the throttle open. I've done the test many times and it seems low for 9:1 pistons to me also. I think it should be closer to 200psi like it was when I first started the newly rebuilt engine. Luckily, the car is still very fast. It still would be nice
to have those 30psi back and too know how I lost them, but that is not why I started this thread. How are your cars doing? What compression ratio pistons do you have and what
are your compression tests showing. What were they at first, how have they changed over time? Thanks.

That doesnt change a thing, as long as all 4 cylinders are within 5-10 psi of each other they are healthy. Plus this just gives you the ability to run more boost and timing without knocking as much as higher comp motors..... my stock 6 bolt had 130psi across all 4 and ran 128-129mph all day long @ 29psi.....

 

[1glaserturbo]

You wouldn't happen to have cams would you? An aggressive set of cams would cause your numbers to be a little lower than you'd expect. Atleast that's what I've been told by many-a tuners

 

[1qkfwd]

My stock 6 bolt had 130-132 across the board and then my built engine with 9:1 pistons was around 155psi across the board. This is at a 5000ft elevation.

 

[LaN-]

Do you have cams? Are you sure your compression tester is sealing properly?

As long as your compression numbers are all in the same ballpark and aren't extremely low who cares.

For example i put my cams in and it dropped compression a little bit, but that doesn't mean anything. Also my compression tester was leaking a little bit, the o ring wasn't sealing 100%.

 

[90laserRSfwd]

195 give or take 1 on all cylinders, my car is a non turbo though but I think it's 9:1 also

 

[turborebel]

Cam gears with stock cams.

 

[fwdeclipse]

I am on the stock 7 bolt bottom end and 150 across with 68k.