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again whats blowby, i thought it wasnt too bad to blow a bit of black smoke out the exhaust, thought it was just cause of the big bore piping that these cars have

whenever i'm at the workshop watching a car on the dyno waiting outside for mine to go on theres always a lot of smoke coming out under full load.

thanks

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Blow by is the gases going past the pistons during combustion, these gasses are circulated to the rockercover where they then get redirected, one way or another, to eventually be burnt again in the cylinders (if you dont fit a atmo vent catch can of filter).

If the rings are starting to wear a bit, blow by will increase, and it would be noticable when opening the oil filler that alot of air seems to be getting forced out. If there appears to be no air being forced out, 'usually' means the rings are ok.

Jimbo2000, the smoke you see from a dyno run is because the AF ratios are intentionally richer during power runs, which helps control detonation.

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how do u know that the compression was 125?

are u sure that the gauge is correct ? if they are all 125 the gauge mynot be right or the engine not normal temp .to check if its bottom end prob ( warn rings or pistons ) do a compression test note the comp on all cil then squirt a small amount of oil in the cil crank a few times then check comp again if it raises say by 10 psi or more u have bottom end prob ( warn rings more than likely )if it doest rise it means warn top end ( valves or valve seats ). the other way is to do a cil leakage test , this is how u do it : spark plug out install i tube with a threaded bit at the end that screws in to the spark plug hole car in gear handbrake on then put compressed air in to cil (150 psi ) and listen far air leaking ( bottom end or top end ) .

note most of the time if engine runs good makes good power doest use a lot of oil and u find low compression ( but all cil the same ) its your gauge or the method u are using not correct so dont panic if all the above are right .

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what they did when they did my test (wasnt paying too close attention so didnt get a good look at what the instrument actually was) they had the plugs out and inserted the probe thing with guage on top into each spark hole (real technical! :) ) and turn the key for about 2 seconds.

wasnt 125 exactly on each one but pretty close.

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standard compression for rb25det is 1.2mpa (12.2kg/cm2)or 171 psi ( apr) limit .9 mpa , 9.2 kg/cm2 or 129 psi . thats at 300 rpm lower rpm = lower comp.variance is 14 psi . rb26 is slightly lower .like 2% lower as it has a lower comp and runs much higher boost . jimbo if urs has a true 125psi u wouldnt have much power unless u run very high boost but i dont think it would be that low .

it would be hard to start if it was that low too ( like taking a few cranks to start it .

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