compression Q's

[95GST2841]

I got 145-155 across the board..

and burn zero oil.. is this okay for a while? am I losing any power?

doesnt leak any either..


motor has 130k on it though so I'm sorta worried about what all the parts I'm throwing at it..

 

[andymoraitis]

You'll lose a bit of power with lower compression and while the numbers aren't awful, 2G's usually pull 170-180 for solid readings. What I'd recommend is retesting your compression by tossing a capful of oil into each cylinder and seeing if the numbers go up. If they do, it's likely a ring seal issue, but with that many miles on a boosted motor, that's to be expected. You could also have a leakdown test performed and verify the same issue that way. Also, please ensure that the motor was run before testing compression as cold numbers are lower than hot due to thermal expansion of the rings, etc. Also, when I say the motor needs to be warm, I mean by driving it and not by letting it idle for five minutes in the driveway.

Other than minor power loss, there are no crazy ill effects and you can still drive it and enjoy it. How long it will maintain it's current compression isn't known, but you can also try using thicker mineral oils (like 20W-50) to see if that helps drive the compression up a bit, but don't let this keep you awake at night. As a matter of fact, most people with decreased compression have a tendency to increase their boost without knocking since there's less compression and therefore less heat in the combustion chamber as a result.

Let me know if that makes sense.

Andy

P.S. For future reference, cams will also lower compression numbers since they have higher lift and duration than stock units. As an example, my stock 2.0 had 160 compression across all four with Comp 200's. My 2.3 which is 8.8:1 as opposed to 8.5:1 reads 170 across. See what I mean?

 

[95GST2841]

I understand.. the motor was cold when I did do this.


would seafoam help this at all?

 

[andymoraitis]

I understand.. the motor was cold when I did do this.


would seafoam help this at all?

Aha Grasshopper! Leave the Seafoam out of it for now and get us some numbers with the motor hot. They should be much better. Also, I really would run a thicker oil on a turbo motor if you're not already. If you insist on synthetic, 15W-50 is fine or if you prefer semi-synthetics or mineral oil, 20W-50 will work like a champ. Florida is hot enough and your motor will appreciate a thicker oil.

Get back to us.

A.

 

[95GST2841]

hm, I will use a thicker oil for sure !


and I will do the compression test with the motor hot.