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Compression Question?

GTRAAH

By GTRAAH,
in Engines & Forced Induction

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GTRAAH Experienced

GTRAAH

Posted
Posted

I did a compression on my 94" GTR R32 it has around 73000kms on it. And all my readings were around

132-135 psi on each cylinder. Is that good or bad, if its low why is it low and how do i fix it. My car is running very nicely though. Its got an remote oil cooler and excaust and everything else seems to be stock.

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GTRAAH Experienced

GTRAAH

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Nissan manual states compression on standard RB26DETT should be between approx 130 and 170 psi (9.0-12.0kg/cm2),with a maximum variation of ~ 14psi (1kg)

You could get slightly higher compression by using a heavier oil, but long term fix is to rebuild engine

So a brand new engine could hold anywhere between 130-170 psi is that what your saying?? or brand new ones usually are all the same at a higher rate???

GTRAAH Experienced

GTRAAH

Posted
  • Author
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New engine should read around 170psi, old engine 130psi, below 130 - serious problems

your engine is a bit tired, but not dead yet.

Hmmmm, so whats included in the rebuild to get my engine back to full compression? and does lower compression mean less performance, because i heard you only have a problem if one is different from the other

Godzilla32 Veteran

Godzilla32

Posted
Posted

Unless there are deep scratches in the bores you should be able to get away with a hone and a set of new rings. If not you will need to re-bore and get oversized pistons. Lower compression normally means less performance but im not sure how low it has to be before it actually makes any noticeble difference. As the manual states possily 128psi?

700HP-GTR33 Mentor

700HP-GTR33

Posted
Posted

73K....is that original with papers?

Edited

It is more important that they all read similar figures than 3 to be good and 3 to be bad.

If you use it daily....just drive it around and don't worry about comp. tests.

If you want to freshen up the motor,for track use and have 4 to 5K in your pocket....re-build it.

Cheers

Abo Bob Grand Master

Abo Bob

Posted
Posted

WTF?!?! The car is obviously running absolutely fine. You have even pressure across all the cylinders and that's what's important. Plenty of gauges show different readings to each other.

All this rebuild talk is a waste of time.

tridentt150v Grand Master

tridentt150v

Posted
Posted

I also presume you had the correct valve clearances [you checked and reset them?] before you did the test??

Take your worst cylinder, squirt a bit of heavier [say] gear oil in it with an oil can, and then do your compression test again.

If it bumps up to +150psi, then its rings/bore/pistons. If it doesn't change much, then its valves/guides.

Do this on a cold motor.

Thats if your curious to know!

GTRAAH Experienced

GTRAAH

Posted
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Valve clearence ?? nah i did exactly what the service manual says accept i didnt turn the fuel pressure switch off. They all came out even around 135psi. i spoke to 2 guys today 1 at Bel Garage (regents park) he said it sounded fine & if they all came out even you dont have to worry and the guy that was working on another car comes up to me and says when i turned the ignition was it cranking fast, i explained it to him by sound and he goes it wasnt turning over fast enough and said always use a battery booster when doing compression test like they always do, Might try that. And another thing i thought was interesting another guy today I spoke to at Hills Motorsports in castle hill and he told me he had like 12 gtrs come through his workshop in the last 6 months with similar pressure like mine and some of them were pretty much new, and goes they were runnning excellent like all of them and told me "we'll he thinks" some GTRs came out with low compression pistons. is that true???? he sounded like he new what he was talking about because he specialises in these cars.hmmm

tridentt150v Grand Master

tridentt150v

Posted
Posted

yeah, I don't think you have anything to worry about myself, I certainly wouldn't be doing anything about it if it was my car. It would have to get a lot worse than that before I'd be thinking engine rebuild time.

And you hit the nail when you talked about compression differences re pistons/head gaskets etc What you have is likely a very healthy normal motor.

Mr Italy! Proficient

Mr Italy!

Posted
Posted

If you're not looking for big power and/or big boost, ignore all of this rebuild talk - you dont need to rebuild your engine if you just use your car to get you from point A to point B, honestly it will be fine for many years to come.

Steve Grand Master

Steve

Posted
Posted
.. if its low why is it low and how do i fix it....

probably why there is 'all this talk of rebuild' that has been happening - the question was asked

perhaps some of the people on here should write to nissan and get them to update their workshop manual, as you seem to know better

the compression is within spec, just, to completely ignore this, and not keep in mind that the engine MAY be ready for rebuilding in the near future, could be asking for trouble.

Anybody wonder why alot of tuners compression test engines before they try an lean on them on a dyno?

would those that beleive the engine is 'absolutely fine' care to enlighten us all on at what compression an engine is getting tired?

and would you pay just as much for an engine that is at the bottom of the published compression range as you would for one that is showing compression at the top end of the range? (not talking about built or decompressed engines here)

GTRAAH, as I said to you in pm, make sure you are using a good FRESH oil (15W50 would be my recommendation for RB engines) and redo the test, I think you will find the results will vary, as too many people use the wrong oils, and dont service their engines often enough.

Cubes Grand Master

Cubes

Posted
Posted

I wouldn't worry too much if the readings are all equal.

Compression testing guages can be quite inconsistent from one brand to the next.

A mate of mine in his VLT tested his and made 160 across all cylinders.. erm 160psi with a 7.8:1 comp ratio. oookaaay.. :P

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