RB25 Compression.

[Chaos the Xile]

If you do a compression test on a RB25, what are the normal or "should be" numbers to look for. I recently did one to mine and showed 120's arcoss the board and just wanted to make sure this wasn't too low, or an issue that would require a re-build...

[Joe]

its VERY hard to give accurate numbers...

why?

too many variables. the test is usually done improperly so that gives false numbers. its more important that the numbers are close to each other rather than a set number.

did you open the throttle all the way when cranking? did you remove ALL your spark plugs before testing? was the engine warm? what about disabling fuel injectors? each gauge can read differently too... theres a small handfull of variables that can give "incorrect" readings.

[minivan_don]

stock r33 rb25det compression is 173 psi.

as mentioned there are a few things that can throw your results off ... if your unsure then swing by a local tuner shop and see what they have to say.

[Chaos the Xile]

Spark Plug out ALL THE WAYOpen Throttle... No, I just cranked...Fuel was Disconnected completely, to ensure no flooding.So OPEN the throttle all the way then crank until the #'s Stabilize correct?

[Joe]

correct

but again, the number itself isnt that important. its the variation between cylinders.

cheap gauges can read TOTALLY different than nice ones.

[SeVa-S13]

^^^ I've seen it.

I also like doing leakdown tests.

[Carl H]

dont forget the motor has to be warm for the readings to be somewhat right, ive seen a motor that was cold read 130, but when warm jump to 155.

[Chaos the Xile]

Yes and when we did a comp test, it was dead nuts cold outside, just pulled the car off of the tow truck and into the garage and began ripping it apart for the test. But since the timing issue I can't keep it running stable for long period it'll keep dying out. So I guess once the inital problem is solved then I can move from there... I don't think the compression is bad when I fisrt got the motor running it was like 155, 160's and was kicking like a pissed off stallion.