compression test question

[charger R/T]

how much oil did you put in the cylinder for the oil compression test?

And what filter are you talking about with the turbo? "does anyone know why it might be blowing turbo seals? i have the braided line and a filter..."
Tim

[speeduphoria]

Quote:

Originally Posted by 87dtna Heh, more than that. I had a fresh rebuilt 360 flattop pistons with 9:1 compression doing about 160-170 PSI compression. So 200-220 is atleast 10:1 if not more.

Well my 2.4 with 8.8CR pistons and head/deck slightly resurfaced= 200psi, guessing that its at 9:1, my buddy's same bottom end 2.4 has the same results so I would say that your rings aren't seated or your clearances are huge or did the test when cold?


If the turbo oil feed line is larger than -3an, you should look into a restrictor for it.

[87dtna]

It had about 500 miles on it, hypereutectic pistons and plasma moly rings (did several runs with WOT low RPM while holding the brake pedal to seat the rings). Did with test with throttle wired open, clearances are to spec the engine was bored .030 over and the shop had the pistons to final hone. I'm about 90% sure the engine was warmed up, because I know there's a difference cold or hot.
One thing I don't get is if only 9:1 CR is 200 PSI, and 8:1 is 150, that would mean that a cummins diesel with a compression of 18:1 or better would be pulling 1100+ PSI which they do not, I think it's about half or less that which supports my number results of a 20-30 PSI jump per point of compression.

[detobias]

don' forget that we can't directly compare Motor A (2.2 turbo) to Motor B (360) to Motor C (2.4) because the other SIGNIFICANT factor impacting the psi <-> CR relationship is cam timing

e.g., a cam with more overlap will have a lower "psi" reading

thats another reason that a 'leakdown tester' is a much more accurate way to troubleshoot ; I mainly use my old-school push-in compression tester to identify Major problems... like a cylinder thats >20% lower than the rest

and of course as 87dtna infers, the CR <-> psi relationship is not linear

[cawcislo]

You could get weird reading for many reasons. Guage could be out of whack. Depending on humidity and barometric pressure you will probably get different readings as well. I never look at those numbers and say oh, cylinder #1 is 130 or 135 whatever. The important part is whether or not they're even across the cylinders. Of course if they're all 90 you probably have an issue. You could use 4 different compression guages and get 4 different results.

[87dtna]

Quote:

Originally Posted by detobias don' forget that we can't directly compare Motor A (2.2 turbo) to Motor B (360) to Motor C (2.4) because the other SIGNIFICANT factor impacting the psi <-> CR relationship is cam timing e.g., a cam with more overlap will have a lower "psi" reading

Very good point. Just the fact that the 360 is N/A the cam is gonna have more overlap. It's wasn't anything crazy because it was in a truck, it was a comp cams 268H which has 268* duration and .454'' lift.

[Timmay2]

Did you make sure the distributor pickup/HEP was also disconnected during the test?

Fuel in the cylinders will really screw with compression tests.

Whatever PSI you got adding oil does not matter- who cares- it just went up a good amount, and thats all we care about. Like cawisco said, how the cylinders are in relation to each other is the important part. All 4 went up, good.

If you had 200psi without oil, then be worried. Its not uncommmon to hit 200psi with oil added at all. Especially if theres other things wrong with the car.

Now about the smoking/oil leak issue- not going to be rings since your compression looks fine.

Check the simplest things first. If you turbo really has 1/4" play side to side youd see some fin damage. That would be hitting the walls then.

How does the car run otherwise? Having timing way off can blow oil past the rings and right out the turbo making it look like the turbo shot. Same with your PCV plugged. Even if the turbo seals are shot again, that is too coincidental on the timeframe, and be lucky if the turbo builder will warranty that. Thats not common at all for a turbo seal to work fine for 1,000 then fail, multiple times, around the same milage. Usually something else causing that.

You mentioned an oil filter- dedicated for the turbo? What is this specfically? Theres been other members here with lots of problems with inline turbo oil filters. Whether it be oil supply being reduced, delaying how fast the oil gets to the turbo during startup, etc. The extra half second or second taken for pressure to build up to pass the filter can make the difference between dead turbo or not.

Id bet on the turbo leaking again, but its not economical to send a turbo off every 1000 miles so we need to figure out what on your car is killing them.