Compression On N1 Block

[Iron Mike]

Hi everyone, I have a question which may seem completely idiotic, but I was wondering roughly what pressures should show on a compresison test for an N1 engine, or even just the standard rb26? I was looking into buying a GTR with a swapped N1 block (that was bought brand new) and i asked the owner to do a compresison test. He told me that compression across all cylinders was about 110psi, and that that was close to what it made out of the factory!!! Last time i knew anything 110psi was indicative of serious trouble! Yes i'm aware that the main point of a compression test is to check that pressure across all cylinders is roughly the same (which it was in this case),but isn't 110 psi across all cylinders too low? Any ideas?? What are your thoughts? what should i be expecting for a 'clean' N1 block with only 40,000 genuine kays on it?

[260tech]

Quote "what should i be expecting for a 'clean' N1 block with only 40,000 genuine kays on it?" Unquote

My question would be "What do I want from an N1 motor with 40k on the block." Or any (hi-po or not) motor for that matter that I was going to buy with an expectation of useful service life. I reckon you could reasonably expect in the range 145 ~ 155psi with 2 ~ 3psi differential if the motor is sweet but I am not an expert. Do some more digging in general maintenance or speak to a trusted mechanic perhaps. I know I would be.

My 2c, waiting for the chops to grill. GW

PS: Happy to be corrected if my expectations are out of wack.

[Moodles2]

About 172psi the service manual specifies as a newish engine (standard internals), about 120psi the manual recommends a rebuild. Although we need more info on the engine, aftermarket cams, cam gears, pistons, headgasket etc. as 110psi could be perfectly normal for that setup.

[MrStabby]

IMO you should get a shop of your own choosing to look at it, so they can test the compression (don't trust what the seller says) and verify its a N1 block. IIRC you can see the 24U marking from underneath when plastic shield is removed, somewhere under the front turbo. Or even better, get your shop to do a full pre-purchase inspection.

Was the compression test done hot or cold? Throttle open? Gauge calibrated? etc. If the tester doesn't know what they're doing the test results are bollocks.

[Iron Mike]

Thanks for the advice. The car's interstate and i'm having difficulty finding a reliable shop to look at it in time (the owner is frequently away for work). I spoke to the guys at one of, or probably the most renound, GTR workshop in my state, and they said not to look into the 110psi too much as long as the pressure was roughly the same for all cylinders. They also told me that a figure of 110psi is very plausible for an engine that is rarely driven (as is the case with this car), or an engine that is tested cold etc. So i've been told to ultimately go with gut instincts and ignore the compression test results (the leak-down test result was also less than 10% which is more important). I've also been advised to have the car run on a dyno to really see how healthy the engine is.....Oh ye, and I had the car put on a hoist so I could check the legitimacy of the N1 block. It's definitely stamped 24U

Edited May 1, 2012 by Iron Mike