Thread: Compression Test after cams

About a year ago we did a compression test of a 91 SE-R from a friend, we wasn't expecting so much since is the OEM engine (JWT S3 cams), results were 150psi across the board.

The weird part is that before the cams the same engine did 125psi across the board and here's the question, did the change of cams raised the readings?

Could it be something else?

Also, how much is considered a normal reading in a JDM 9.5 and 10:1 engine?

Stock is around 180, main thing to be sure of is consistency. As long as they're all withing 5-10 psi of each other it's ok.


At the same time when I did my cams, I messed up the timing and it only read 150 across.

my buddies nx2k with a jdm motor, not sure if 9.5:1 or 10:1 but with the numbers it made im gonna guess its a 10:1 motor.

Its been boosted for 2 1/2 years and almost 30k miles and the numbers wer 175-180psi across the board.

Most 9.5:1 motors ive seen make around 160-175 across the board.

But why would the readings raise after the change of cams?

usually they lower during cam upgrades. Just like when we put the s4 cams in, vac usually pulls only 16-18 compared to 19-21 with stock cams.

Ive seen this on every cam upgrade ive done.

But your compression is more based on how well your motor is sealing internally.

I know, that's why I can't find the reason going from 125 to 150psi in my buddies car