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Compression Test Results... Good Or Bad?

Beef

By Beef,
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Cubes Grand Master

Cubes

Posted
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125psi is pretty low.

the figures seem TOO close together. if they were that low i would think there would be small variances of 3-5psi between them at least. thats my opinion rather than expert advice so just get another one done somewhere else.

I tested mine when dropping the new injectors in, it runs wiseco forged pistons that have been setup on the looser side so they do slap a tad when cold.

When I finally got around to testing the comp ratio the motor had done around 20,000km's, wasn't using any oil.

To my suprise ALL cylinders were equal apart from cylinder 3 that read 1psi different. :D

I got 153psi or there abouts I don't remember exactly but it was around the mid 150's.

So when warm and the pistons fill the bore a little better no doubt I will receive a higher reading.

So yes, equal values in every cylinder is possible. :dry:

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Cubes Grand Master

Cubes

Posted
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it is possible, but at the 125psi level you'd probably start to get figures that arent so close together, let alone exactly the same.

Yes for such a low level, but it may just be the guage. Which is why the general rule is to go off variation.

Cam timing could also be out, maybe rebuilt some time with lower comp pistons, thicker headgasket.. Could be a number of things.

My Rb20DET with std cam timing saw 145psi in all cylinders, that was at 60,000km's. Cam timing does make a difference to the comp ratio.

Squishy Experienced

Squishy

Posted
Posted
ok, is your car still running fine?

using oil?

what do people think about this?

Beef

It is running pretty good for a 5 cyl but using a bit of oil...

i put about a litre of lucas in it on the weekend and she is running good again.

It still boosts and goes hard.. emm did i mention that it smokes a shitload!! :P

It only has to last me a few more weeks till i drop a RB25 in her.. then i will re-build the RB20 to sell.

Beef Community Regular

Beef

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Cam timing could also be out, maybe rebuilt some time with lower comp pistons, thicker headgasket.. Could be a number of things.

Cam timing does make a difference to the comp ratio.

oh ok, well im pretty sure that the timing was on 22degrees when comp test was done, i have taking it back to 20degrees, so maybe it may be a litle lower/higher this time?

which way?

Tim

Beef Community Regular

Beef

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Um, cam timing, not ignition timing. If you want to check the cam timing you need to take the belt cover off & check that the marks on the belt match the marks on the pulleys.

oh sorry, ha ha

how would one go about adjusting the cam timing.... can it be adjusted or do i need to get another timnig belt or something?

Beef

Beef Community Regular

Beef

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OK just went and got the compression re-tested.....

1. 145psi

2. 150psi

3. 150psi

4. 145psi

5. 150psi

6. 150psi

so i dont know what the other F**K head was doing, maybe he tested when cold or something....

so does this sound like a better number....

maybe it will improve when i do the oil change that is past due..... and also flush it out..

what you think...

check the pic, its my baby gettin checked... :P

compcheck.bmp

Cubes Grand Master

Cubes

Posted
Posted

Nothing wrong with 150psi odd.

It was probably just the other bloke guage and or didn't give it wide open throttle.

or... maybe he wanted to rebuild your perfectly fine engine. :D

OK just went and got the compression re-tested.....

1. 145psi

2. 150psi

3. 150psi

4. 145psi

5. 150psi

6. 150psi

so i dont know what the other F**K head was doing, maybe he tested when cold or something....

so does this sound like a better number....

maybe it will improve when i do the oil change that is past due..... and also flush it out..

what you think...

check the pic, its my baby gettin checked... :P

Beef Community Regular

Beef

Posted
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Nothing wrong with 150psi odd.

It was probably just the other bloke guage and or didn't give it wide open throttle.

or... maybe he wanted to rebuild your perfectly fine engine. :P

yeah maybe he wanted to make himself a few extra bucks.... but to eliminate teh chance of a dodgy mechanic i actually watched them do it and saw the results with my own eyes...

oh and..... what you mean by they probably didnt give it wide open throttle, they dont start the engine, they only turn it over 4 times....... its never actually running.....

Beef

Mr Italy! Proficient

Mr Italy!

Posted
Posted
oh and..... what you mean by they probably didnt give it wide open throttle, they dont start the engine, they only turn it over 4 times....... its never actually running.....

Beef

Ofcourse it wont start the engine, it has no coils or spark plugs - what he means is that the throttle is flat to the floor. Apparently this is the correct way to do it, otherwise you will get incorrect readings.

Beef Community Regular

Beef

Posted
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Ofcourse it wont start the engine, it has no coils or spark plugs - what he means is that the throttle is flat to the floor. Apparently this is the correct way to do it, otherwise you will get incorrect readings.

um der freddy........

the way he said it sounded like he was talknig about a dyno test or something.....

SECURITY Grand Master

SECURITY

Posted
Posted

WOT will allow air to enter the cylinder easier and free'er which is why the results are more accurate. not doing the test at WOT may give you readings of 10-15psi less which is what i've noticed in the past.

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