Compression test

[Navigueur]

Doing PPI: Compression test gives 140 on all except middle cylinders. One middle at 135, other at 130. (7% difference)

Did leak down test on 130 and 135 ones: 0%

Engine has 122,000km (76,000 miles) and is a 1989 3.2 in a carrera cab.

Comments?

[Drisump]

Originally Posted by Navigueur

Doing PPI: Compression test gives 140 on all except middle cylinders. One middle at 135, other at 130. (7% difference)

Did leak down test on 130 and 135 ones: 0%

Engine has 122,000km (76,000 miles) and is a 1989 3.2 in a carrera cab.

Comments?

I'm not sure what that particular engine should be compression wise, but it sounds good to me. I'm curious about the "0" leak down number though, the escaped pressure has to go somewhere ie. past the valves or rings unless the combustion chamber is somehow a little bigger than the others.....(perhaps you have a little carbon build up in the 140 cylinders) . My engine (a 3.2 Euro) tested at 170 across the board when the PPI was done four years ago but since the N. American engine is a lower compression version, it is probably good. I'm sure others with more knowledge about this engine will chime in soon. Cheers

[kanadary]

140 psi seems low to me, my ppi for an 87 with 70k miles was 175-180.

[ossiblue]

Who did the compression test? Was it done cold or with a warmed engine? Was the throttle wide open? Are the numbers an average or from only one test? At what altitude are you? Ditto for the leak down, save altitude and throttle position.

The major concern in a compression test, aside from radically low numbers, is the difference between cylinders and your low numbers are certainly within range. I, too, would be suspicious of 0% leak down. How, exactly, was the test conducted?

[kanadary]

it was done by chris german auto, he's the tech expert for carreras in pca. i live in seattle wa so i'm not sure what the alttitude is.

[NewfieMZ3]

That compression is definately low for an '89 3.2.........should be around 170 + on a decent engine....................and 0% leakdown? Never seen that before........especially on cylinders with low compression. My uneducated opinion tells me the test was not done properly, try another shop.

[Navigueur]

Thanks for the comments...

Engine is original, not rebuilt...

Test was done in Montreal, 90 feet over sea level.

Engine was cold; one test only; all plugs removed (they looked OK)

Throttle was closed. I know that is wrong, but could that explain low readings?

Leak down was done only on 130 psi cyl., with air, of course, with dual Gage instrument, and I saw it stay at 0%, for about 10 seconds!!!

Mechanic is most reputed Porsche independent mechanic in this area!!!

He said it was normal; I was looking here for a second opinion...

[cashman]

My 1989, 3.2 Cab tested 160-165 PSI with a 2% leakdown.
Mark

[Targalid]

Quoting from Wayne Dempsey's How to Rebuild and Modify Porsche 911 Engines: "With the engine warm, install the compression tester into the spark plug hole....Make sure you place your foot all the way down on the throttle. This will allow maximum airflow into the engine; otherwise your compression readings will be off...." page 14.

[ibeaudoin]

Originally Posted by Navigueur

Mechanic is most reputed Porsche independent mechanic in this area!!!

He said it was normal; I was looking here for a second opinion...

I'm curious to know who did it.

[Drisump]

It seems that those numbers are indeed on the low side. Like others have said, the engine should be warm and that (with the throttle open) should bump up those numbers. Without the throttle being open, there is limited air flow to fill the cylinder before compressing, giving you a lower reading. According to the "Porsche 911 Performance handbook" by Bruce Anderson, a healthy engine should test out between 130-170, be within 15% of each other and have no more than 3 to 5% leak down in any cylinder. Cheers

[Eagledriver]

With the throttle closed the test was done incorrectly, hence the low numbers. Since they are all similar I think you can at least conclude that none of the cylinders has a major problem. No engine has a leakdown of "0" so I don't know what to make of that test. It might be worth doing a leakdown on all cylinders at a shop that knows what it's doing. That being said I would be comfotable with that engine if it runs well and the plugs look good. Try to have someone follow on a test drive and look for oil smoke on accel and decel. Valve guide on Carrera engines can be bad at your milage.

-Andy

[E Sully]

I would not trust the leakdown. First I would verify the gauges by seeing the reading they give before they are threaded into the cylinder. And what air pressure was used? Was the cylinder at TDC? There should be some leakdown, especialy with the engine cold, low compression and the mileage on it. Try again right after driving till the engine is completely warmed up, and the throttle open. My 86 engine needed valve guides at 68,000. It currently has 185+ lbs on a compression test with 3,000 miles on a top end rebuild.
YouTube - Compression

[Navigueur]

Thanks for the comments, Guys...

I will have the test redone properly on the next visit to the mechanic...

I don't want to embarrass him by identifying his name... in public...

PM if you need to know!!!