Compression Test Results And Displacement Increase

[GTRNUR]

Hi all,

Just did an oil change, pulled the plugs and did a compression test on my newly aquired R33 GTR vspec. I am very happy with the results.

All cylinders came in around the 180-185psi mark.

I've done a background check on the car and discovered that the engine is not the original one that was installed in the car. THe engine runs very strongly, and has great off boost torque. Cruises comefortably under 2000 rpm in 5th gear at 60k. Great boost response too making noticable boost at 2000 rpm in the taller gears.

It is possible that my compression test gauge is a little off, but I am wondering what the effect on compression is when running 0.020" and 0.040" oversized pistons are on compression tests.

Ive used this same gauge on an RB20DET and it measured 150-155psi, which sounds right for an RB20 so the gauge cant be that far out.

Thoughts anyone?

Cheers,

Ian

[deant1]

A guy just did a compression test on the forums (can't remmeber where the post is) he got 180 on all 6 on his 25. So i guess the reading on yours will be good. 26 and 25 wont vary too much.

[BOOSTD]

my rb25 and my rb26's both get 150psi for 9:1cr. 180psi does seem high....

[R31Nismoid]

Its all in the way you do it.

As long as there isnt a lot of variation between each cylinder then there is nothing to worry about

[GTRNUR]

Dam, so the higher cylinder pressure really isnt indicating anything....

I suppose knowing what cams are in it as well would also help work things out, cause overlap will effect dynamic compression and cylinder pressures. I'm taking the timing covers off tomorrow to check the condition of the belt and maybe see what kind of cams are in there.

Cheers,

Ian

[Duncan]

yep all those things can affect the results, but generally they lower not increase it. Also how you do it generally lowers the readings too eg throttle not open, engine cold or battery dying.

171psi is max factory spec

[Butters]

Seen some wildy in-accurate comp test gauges. Some read 20 - 30 psi of what they should. Doesn't matter though as said above as long as all cyclinders read about the same. Just means you can't really compare the number to the factory manual.

Good ol super cheap china comp gauge FTL.

Edited June 11, 2007 by Butters