compression test results

[wreckedhead]

i got my nos kit in today and i did a compression test to be safe,

Test results

piston 1) 135

2) 145

3) 140

4) 130

5) 135

6) 135

Does anyone have the standard compresion test of a rb26 motor. just wanna see if my compression is low.

[Chris32]

I think the key is its all pretty even, every gauge reads differantly, so I'd say its all ok

From factory I have heard figures of 150-160psi

anyone else?

[dan_the_man]

erm I heard factory is way over 160...

[Sydneykid]

Compression test is all about consistency, the absolute number is not comparable. Cranking speed, engine temp, ambient temp, battery condition all make a difference. That's why a leak down test is superior, it removes most of the variables.

[Chris32]

the R32 manual says 171psi at 300rpm

As SK says, contistancy is the key and a leak down test is far better

[benm]

What is the difference?

[wreckedhead]

yeah whats the differnce, if the compression is almost the same through all cylinders

[vspecv]

i have seen engines with bent valves and broken rings or ring lands still comp up ok.

leak down is a better tool for diagnosing any problems.

leak down pumps the cyl with air and the guage tells the % that leaks past rings, valves etc

[predator]

I have got around 135-140psi across the range on an rb25det engine.. which was otherwise fine.. factory is meant to be 172psi or thereabouts. I think it can just be the guage - mine was like $70 i think its always shown pretty low on the few engines I've tested it on.

[Sydneykid]

As previously posted, personally I wouldn't stress over the absolute number, it's the comparison that's important. The manufacturer quoted compression test relies on the engine being up to operating temperature. Did you do it when the engine was hot? Not reasonably warm, or even worse, stone cold so you didn't burn your hands when removing the spark plugs. It has to be at operating temperature, that's 80c or above or halfway on your std temp gauge.

Secondly it is done with zero resistance, no dragging clutch, no tight fan belt, no air con compressor etc etc. No electrical load, this means you can't have the radio on while doing the test. Thirdly it is done with a brand new battery and starter motor. All this means a faster rotation speed during the compression test.

I have personally never achieved factory compression in any car I have tested. So unless you unbelievably unlucky and all cylinders have worn exactly the same amount, the very close results for all 6 should give you confidence.

[2fardown]

15 PSI difference from Piston 2 - 4 is a little worrying.

[Sydneykid]

15 PSI difference from Piston 2 - 4 is a little worrying.

I'll bet he started at cylinder #1 and the engine cooled down by the time he got to #4. :headspin:

Or the battery ran down a bit from the cranking

[wreckedhead]

actually the car was sitting on a hoist for 2 days, and the second day the car wasnt started so it was stone cold while doing the compression test, also battery was a little flat.

so hopefully the compression test results were ok.

[B-Man]

I did a compression test the other week on my car - 125 PSI exactly accross all cylinders (That's after a rebuild and run it)

Seems low - but it still pulls like a $50 whore - so all good

Ummm - that's when the AFM and ECU are working

[Jimbo2000]

same b-man, (except for the rebuild) 125 across.. but they said that they think my car has been decompressed/compressed (can remember exactly what he said :Oops: ) at some stage previously

so whats involved in a leak down test?

where to get it done? is it expensive etc

[B-Man]

Mine has thicker head gasket and cams - so that't prolly why

Any good place can do a leak down test. I think UAS can as I asked John about this...

It involves taking a plug out - shoving compressed air into the cylinder and leaving it there for a while whilst measuring any pressure drop - if the pressure doesn't drop - all good - if it does drop , there may be a problem.

[benm]

Seems low - but it still pulls like a $50 whore - so all good

Where do you find those type for only $50? :boobies2:

[wreckedhead]

also forgot to add that i have thicker metal head gasket and non standard cams.

[Morgs]

My results were 160psi in all but number 5, which was 155psi, standard motor.

[Cameron_Datto]

You should also Stop the injectors from injecting fuel into the cylinders when doing a Compression test .. some thing that most people for get to do..