Compression test results

[puddy]

I've wAnted to do a compression test for a while to see if my 3.3 motor was healthy. So tonight I did the test with help of a neighbour. The results were all from 130, 135 or 140, on a warm engine. This seems to be good to have cylinders so close, but do these numbers seem low? I've read many other should have around 180 or so.

Thanks. Chris

[turbo owner]

Lower compression engines like our turbo cars have won't have high numbers.

Saw the 8.5-1 CR down below, you could be a little low. Do a leak down test and see what that says.

[puddy]

Ok so what I have isn't unusual?

[T77911S]

the numbers look good.

it also depends on how you did the test.
if you crank until you reach max compression then that's about what I have.
someone taught me a looong time ago to do 6 stokes. when I do that I get about 120 on all 6.

I have also done test with the throttle open and closed and did not see any difference.

[Tippy]

Sounds fine, but did you pull the plugs and hold it WOT?

[puddy]

We pulled all plugs on bottom side, since i'm twin plug. Held throttle open and turned it over until a couple seconds after the gauge stopped moving. Seemed to work out fine.

[Black_Hat]

I just did both compression and leak down before dropping my motor to do more mods.
The compression tester is a new IEC .
I do have small reliefs cut in my pistons for a high lift cam.
I have 10 k miles on a full rebuild
I measured 150 psi on every clyinder
the leak down was less than 1% on every cylinder

[Black_Hat]

stock compression
cold motor

[Black_Hat]

1991 C2 turbo

[puddy]

Cool thanks for the info Blackhat!

[Pat RUFBTR]

It seems to me that a test of compression is always made when the engine is hot.

[puddy]

Yes the engine ran for a few minutes before testing, temp was up to 120.

[puddy]

As a follow up on this. My car uses alot of oil, about 1 litre per 750 kms / 466 miles. There is approx 20000 kms / 12,500 miles on the motor. Could this high consumption be from a worn out turbo or more likely worn rings? It does puff some smoke on start up sometime, but not every time.

[T77911S]

were the valve guides done on the rebuild?
did you replace the rings?

sure, could be turbo using oil. if no shaft play, boost is good I would not worry to much.
check the pressure pipe for oil.

can timing and cam will effect numbers. the later the intake closes the lower the number.

I did not notice CR and cam before.

[full quack]

With that much oil consumption, one would think you would see a telltale sign of faint smoke in the exhaust.
In a terribly over simplistic general sense, oil consumption can be translated into 2 main categories.
1.) Smoke during acceleration = rings.
2.) Smoke during deceleration = valve guides.
3.) Throw a turbo into the equation and you add turbo seals???

Others should chime in to help out here I'm sure.

Mark

[puddy]

I will ask the PO if valve guides were done on the last rebuild.

No one at the track has noticed me smoking. On acceleration or deceleration. I've asked a few people.

I may get my turbo tweaked over the winter, I actually spoke to a well known local builder who says the K27's were very bad for oil consumption, he actually recommended I build a larger oil tank for the turbo. He said something about on shut down, the oil in the lines drains into the tank and get burned on next start up. At least I think that's what he tried to tell me...

[T77911S]

do you fill the oil up to the max?
I run mine less than half way

take a look at the plugs

[puddy]

I run the oil level in the middle. But it's usually under middle.

Plugs looked normal last time I had them out. Which was to do the compression test.

[Jeff Alton]

Have you done a leak down test yet?

that will tell you if you have a ring issue. It will not identify a valve guide or vale stem seal issue mind you.

Start there, and report back your findings