RB26 down on compression.

Hi all,

Fist just a intro. New to tuning and sorry if this is a stupid question.

Recently had my R32 GTR tuned after fitting some new cams.

The car was hugely over fueling on cold starts. Had it out for a few days for a show, wasn’t drove that hard. Onto boost a few times. Then noticed it was slightly down on power. Held off boost and left it back to sort the cold start. Had noticed some petrol in the oil catch can at this point to.

So done a compression test Which should be 150-170

came back as 85 89 109 119 102 97.

which is worryingly low. (Need to try another gauge on it just to be sure)

The question is, if this was caused from fuel wasing the oil off cylinder walls and wrecking the piston seals would I have any reason to say it was the fault of the tuner ?

Touchy subject as I hope it’s not and he’s also a mate but again don’t wanna have to pay for a rebuild

It wasnt compression tested before hand as it was rebuilt 5k miles ago by previous owner with new wiseco pistons forged rods etc etc. So didn’t think it needed one. Hindsight’s a wonderful thing tho.

thanks !

Was the car warm and the throttle open doing the compression test? Forged pistons can have a larger piston to bore gap to allow the piston to expand as it warms up therefore readings can be low when engine is cold. However Still quite a large difference in readings

Try another compression gauge and do the test with the engine cold and warm , let the engine reach operating temperature and do the test.

Also do a leakdown test is a better indication of the engine condition. if the overfueling condition is only on warm up and the engine is only 5k miles

it could be other problem . leakdown test is good indicator try that and tell us the results .

I'd be very surprised if over fuelling would result in low compression. It's almost an old wives tale to be honest. While yes, over fuelling can wash the bores, this needs to happen over an extended period of time and it needs to be dramatic to have any measurable effect. I'd try a hot compression test and back it up with a leak down test so you can find out where the leakage is occurring.

Picking the car up tomorrow,

Nobody seems to do leak down tests local to me (N.Ireland). One Guy I found isn't available until the end of the month.

Have got the lend of another compression tester, Will give that a go and post results.

Honestly for the small outlay a leakdown tester is essential if you're going to be messing with cars. Here's the first one I found online with a quick google - https://www.jegs.com/pt/Leakdown+Tester