I just did a compression on my engine and i am worried it is a bit low. Here is the details. Cyl. 1... 170 cyl 2... 170 cyl 3... 165 cyl 4... 170 It now has 870 miles on te rebuild and it is 9.0:1 pistons.

Also We jsut did a compression on my friends rebuilt engine and the numbers came out like this... Cyl. 1 180 cyl. 2... 190 cyl 3... 200 and cyl 4... 210 He has 3000 miles on his engine. and it is 10.0:1 compression.

Are those numbers ok.... thanks.

 

Sounds good. All your numbers are within 5psi. I'm not sure though.

 

I have a b16, and mine came out between 200-215.

 

What cams do you have in the motor?? those numbers look good also the best way to test a motor is with a leak down tester. also depending what cams you have and what your cam gears are set to you will get lower or higher psi. but the lowest number on a comp check should be 155 if lower you might have some issues.

 

I have an ITR intake cam but a stock GSR exhaust cam. Would that lower or raise the compression compared to a stock cam?

 

Those seem like great numbers.

 

The cam wont affect the numbers either way. Your friends car is a little off. His numbers have quite a spread. Did you do the test with the engine warm or cold?
That will affect the outcome.

 

they were warm. We did his first so his engine was even warmer than mine. What will that do to the numbers?

 

warming the motor will cause the rings to expand more resulting in higher numbers, also make sure you have the throttle full open when compression testing.

 

your numbers look good, mine had 9.4 comp and my numbers were about 190.

 

You are SO WRONG!!!!!!!

A cam with more duration and overlap will allow more "blow thru" and less of the intake charge to be trapped when the valves shut, and compression begins.

Also, just changing the cam timing will effect the compression numbers.

4 degrees adavanced, I got 210-215 on my Z6
zero, I got 185-195
3 degrees retard, I got 165-175 range.

Same motor, same cam, different valve timing events.

EDIT: Also did anyone note the different compression ratings between the 2 motors???


[Modified by Mista Bone, 6:17 AM 12/27/2002]

 

Compression is good. Don't forget you built the motor for turbo. My buddy had a 99 Si with a built motor with 8.5 to 1 compression and he was at 160-165 across the board.

 

its fine ...

as for your friends, since the numbers kept climbing for each cylinder you tested (assuming 1 to 4 in that order) ... looks like you did not disconnect injectors so pressure kept climbing up ???

either way no reason to be concerned.

greg

 

Any reason why this is needed?

(not trying to flame, just rying to learn)

 

so that you can let as much air in as possible

 

We did disconnect the injectors. We did it the same way as we did mine. Any other suggestions why his numbers climbed like that?