RB25det

[Julsmadrid]

Hey all just wanting some advice. I’ve just compression tested my RB25det and these are the following results 

Cyl 1 - 135psi

Cyl 2 - 135psi

Cyl 3 - 120psi

Cyl 4 - 140psi

Cyl 5 - 130psi

Cyl 6 - 125psi
 

do these numbers seem ok. 
Thanks in advance 

[GTSBoy]

1 hour ago, Julsmadrid said:

do these numbers seem ok. 

Depends on what you mean by OK. First up, was this done cold or hot?

Are they reasonably consistent? Yes, they are reasonably consistent. Could be better. But unless it has had a build at some point, it is a ~30 year old engine and you'd expect some variation. Some of the difference could also be in user technique

Is it good compression? Well....not numerically, no. New they were >160 psi. The one at 140 would be fine, in that context. If they were all ~140, you'd be reasonably happy. But the one that is @120 is twice as far down from the original numbers as the one @ 140. But.. (again)... technique can play a part in the absolute magnitude of these numbers, and the quality/state of repair/accuracy of the pressure gauge is not known.

In the context of the above, the compression tester that was used last on my car is regularly compared to a known good pressure gauge. Not calibrated, exactly, but compared to a reference instrument that is not used for any other purpose, so cops no abuse. So we can trust the measurements off that tester. But another tester in the same workshop wasn't being compared against the standard and was reading a good 30ish psi lower. When you're reading 100 psu but the engine is really doing 130, you can make bad decisions.

[MBS206]

I've always work on a 5% variation being acceptable in a petrol engine. Google reckons 10%. You could see if any of the translated service manuals give a factory allowance too.

As GTS pointed out, new is also a chunk higher too.

 

The real question is, how is the vehicle running? If it's running great, who cares!

[Julsmadrid]

Thank you GTSBoy and MBS206

I have done the compression test with the motor out of the vehicle, reason for the test was to see if I needed to remove the head and do rings etc while its out. I'm in the process of respraying the vehicle and tidying up a few things. Story behind it all is I've just purchased the skyline and it was running when I got it, never drove it on the street though as I wanted to pull it down and do it all up again before registering it. the gentleman I purchased it from told me the motor has a forged bottom end and has a decent tune through it but I was going to pull the sump off anyway to see if it is a forged bottom end. that's why I thought id do a compression test beforehand. 

[TurboTapin]

On a cold engine, those numbers look more then fine to me. 

[Dose Pipe Sutututu]

Ran in more boost, ask questions later 

[Dose Pipe Sutututu]

*Ram