2G Compression test results

[Twinturbo120]

Cylinder 1 = 180
Cylinder 2 = 171
Cylinder 3 = 170
Cylinder 4 = 161

How long do I have?
Should I be worried?

 

[LiquidX]

That's some IMO big differences but you are still well above the service limit. I would do a leak down test to see why your compression is odd, perhaps a valve issue.

 

[Twinturbo120]

That's some IMO big differences but you are still well above the service limit. I would do a leak down test to see why your compression is odd, perhaps a valve issue.

It's not that bad, I mean Cylinder 4 is weird, but the rest are fine I guess.

 

[BogusSVO]

You are right at the 10% area most text books talk about from low to high...

Your avarage is 170.5

now 5% up would be 179.25

Low would be 161.75

The low and High diffrences can be from many things, the block deck is not square to the crank center line, one rod is a few thousand longer, the stroke could be a little off, a combuston chamber can be a little larger or smaller from the casting process, more wear in one cylinder than another, a ring could have lost some tention..... The list can go on and on and on....

As LiquidX said, you are still above the service limit.

I also agree run a Leakdown test, you may find something.. you may not

 

[Pipnorcali]

When I did mine it was 180 on 3 and 165 on #4 and I've had a dyno day and a few track days with no problems

 

[sciondan]

Did you do a dry test first, then wet? If not go do it again and report back. If you do and cyl.4 jumps back up then the rings on #4 are getting worn. Either way those numbers are plenty high for good combustion. Actually seems a little high for a turbo motor. Whats the stock spec? On my 90 gst it was 160psi in the factory service manual. Mine came out at 150psi across the board at 90k miles.

 

[gofer]

The standard value is 178psi and the service limit is 133psi, I believe. The "limit" between pistons is a difference of 14psi so, do as sciondan said and pour a SMALL amount of motor oil down the #4 spark plug hole and do the test again.

If compression INCREASES it could be a piston ring or damaged cylinder wall. If it remains at 161psi, as before, then it could be a valve seat or your head gasket.

On my 90 gst it was 160psi in the factory service manual. Mine came out at 150psi across the board at 90k miles.

That's because the 1g's run a lower compression piston than the 2g's however, it sounds like that motor was in great shape after 90k.

 

[FLASH1970]

If I remember right, I had 180-180-180-160 (give or take a few) on my 99 when I bought it with 178k on it. It now has 239K on it and still going 120 miles a day...

 

[Twinturbo120]

If I remember right, I had 180-180-180-160 (give or take a few) on my 99 when I bought it with 178k on it. It now has 239K on it and still going 120 miles a day...

Lol Holy crap man thats one strong engine

 

[TSi-Rocket]

It would only take a small nick in a valve seat to cause a slight leak but I wouldn't be worried at all with those compression numbers.

 

[romeen]

Did you do a dry test first, then wet? If not go do it again and report back. If you do and cyl.4 jumps back up then the rings on #4 are getting worn. Either way those numbers are plenty high for good combustion.

The standard value is 178psi and the service limit is 133psi, I believe. The "limit" between pistons is a difference of 14psi so, do as sciondan said and pour a SMALL amount of motor oil down the #4 spark plug hole and do the test again.

If compression INCREASES it could be a piston ring or damaged cylinder wall. If it remains at 161psi, as before, then it could be a valve seat or your head gasket.

Since our pistons are dished oil is going to accumulate on top of the piston thus raising the results. So it's not a reliable way to test the piston rings.

As others have said, a leak down test would be best if you are really concerned. Personally, if the car is running good I wouldn't worry about at the present time.