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Compression Test Results

Mumbo#5

By Mumbo#5,
in Engines & Forced Induction

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Mumbo#5 Collaborator

Mumbo#5

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Hi all

Just did a compression test on my car and i got what seems to me to be fairly low compression. All of the cylinders were 10 psi within each other at 120-130psi. I did the test at NOT.

The engine has been rebuilt about 10,000kms ago and has arias forged pistons, 20thou over and 4 thou ring gap.

Can anyone shed some light on why its so low? or is it normal??

Thanks in advance

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Guilt-Toy Grand Master

Guilt-Toy

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i compression tested my engine 800km after it was built and i got a reading of 120 in each cyl. yes it is a bit low in compression but that good thing about that is that its safe to run high boost and high ignition timing so the only difference you will notice to a engine with 160 - 170 compression is the driveability off boost (mine is a 3 litre so its still really good anyway) and you can run more boost and more timing then they can...

Hi all

Just did a compression test on my car and i got what seems to me to be fairly low compression. All of the cylinders were 10 psi within each other at 120-130psi. I did the test at NOT.

The engine has been rebuilt about 10,000kms ago and has arias forged pistons, 20thou over and 4 thou ring gap.

Can anyone shed some light on why its so low? or is it normal??

Thanks in advance

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Nabil Rising Star

Nabil

Posted
Posted

I assume your engine builder has either deliberately or accidently,

blueprinted your engine with a lower compression ratio.

Possibly made an error in calculating your desired compression ratio.

Could be anything from the thickness of the head gasket, pistons used, the

amount the head/block was decked etc.

This just means your engine will be more less likely to detonate

than another engine with a higher comp. ratio.

Cheers,

Bill

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Mumbo#5 Collaborator

Mumbo#5

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its got a standard nissan headgasket with ARP studs. I didnt do the test with the injectors not operating so this could have also gave me a lower reading. The workshop that put my engine together new I was eventually going to run really quite high boost so I'm guessin they did that to suite.

Sweet :yes: thanks lads

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wrxhoon Grand Master

wrxhoon

Posted
Posted
Hi all

Just did a compression test on my car and i got what seems to me to be fairly low compression. All of the cylinders were 10 psi within each other at 120-130psi. I did the test at NOT.

The engine has been rebuilt about 10,000kms ago and has arias forged pistons, 20thou over and 4 thou ring gap.

Can anyone shed some light on why its so low? or is it normal??

Thanks in advance

Thats big variance for a new engine , it should be a lot closer, thats the worry not the numbers, numbers will depend on lots of things , even the gauge the way you done the test etc....

I hope you have more than 4 thou ring gap otherwise you will have broken rings, unless you mean 4" piston to bore clearance .....

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