Compression Test Results.

[un1eash]

Borrowed a compression tester of garrick, cheers for that. Just done a check this morning just to see if all is well and the results were...

1.179psi
2.189psi
3.179psi
4.180psi

Which all looks good but i then realised that i didnt do the test with the throttle fully opened, re-did the test with the throttle open and they all read around 200psi. Why is this and are these readings to high?

My exhaust is still leaking at the manifold so dont know if this will affect it, finally getting this fixed next week thanks to garrick again for the manifold and jinxy for the gaskets.

[b2hbm]

I think the reason it's higher with the throttle open is that you're compressing something rather than just spinning the engine.

Personally I don't hold too much faith in actual readings from these things - unless they've been calibrated before use then they can be significantly out.

However I do hold faith in the set of readings - any significant variation between cylinders is valid even if the gauge is 10% out. So your figures seem ok to me....

[crazybrightman]

with standard c/r should be about 180psi. obviously if you are running longer duration cams then the pressure will be a bit lower or have had the head skimmed the the pressure will be a bit higher. they seem ok and even enough though.

[Icsunonove]

re-did the test with the throttle open and they all read around 200psi.

Because with the throttle shut the pistons are pulling against a partial vacuum and therefore are not drawing in as much air as with the throttle open.

[kevin..in]

firstly you don't know how accurately calibrated the comp. tester is.
so the actual readings aren't totally relavant
what is good though is that they are all close, so nothing to worry about

[System-G]

Chris was using my tester and it's calibrated just fine

For what it's worth Chris, I do two tests with the throttle closed. Never bothered with an open throttle test.

One cold - before the engine has been turned over after a long rest.
One hot after a run to get everything up to temp.
As long as all the readings are all close and within tollerences, no need to worry.