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Join Date: Apr 2012
Location: Santa Monica
Posts: 172
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3.6 Cayenne 958 Compression test results, ok? [I know its not a 911 lol]
Hey all
 I have been scouring the internet to get an accurate resource of information. I had my mechanic compression test a 120k mile 2017 3.6 v6 base cayenne motor to see if its healthy. The results are in, and they seem low. But I can't find what the factory spec should be. This motor has a 10.5 compression ratio. Shouldn't that be closer to 155psi? CYLINDER #1- 135psi CYLINDER #2- 130psi CYLINDER #3- 130psi CYLINDER #4-135psi CYLINDER #5- 130psi CYLINDER #6- 130psi
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02-19-2025, 04:10 PM
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Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,480
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Much like a 911, 120k on the motor, your numbers are going to be down from new.
The compression check has to be done warm, throttle body opened, and free to spin with all plugs removed. As long as you’re getting good service, don’t look for problems. Bruce |
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02-19-2025, 05:19 PM
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PCA Member since 1988
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Your mechanic's compression gauge may be out of calibration. The more important indication is that the numbers are all within 5psi. That is very good.
And as Bruce recommended, if it ain't broke, don't fix it. Just drive it.
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1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners. Cars are for driving. If you want art, get something you can hang on the wall! |
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02-19-2025, 08:21 PM
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Join Date: Apr 2012
Location: Santa Monica
Posts: 172
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Thanks all. Sounds like the engines in ok health based on the numbers being close together.
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02-19-2025, 09:42 PM
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Join Date: Mar 2019
Posts: 1,611
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I'm with Pete, his compression gauge is off. Tell him to change the Schraeder valve in the end. And he can't use a tire valve stem core, either, the springs are too strong.
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02-20-2025, 06:44 AM
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Registered
Join Date: Feb 2004
Location: denver
Posts: 1,146
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There are many things that can effect a compression test, some already mentioned. Cranking pressure will not usual equate directly to compression ratio unless the cams have no overlap. Most engines have some overlap so when you are cranking some of the air is being blown out before the valves are fully closed. Two engines with same pistons one with racing cams one with mild cams, Racing cam engine with lots of overlap will have lower compression test than mild cam engine. altitude that you are testing at will also effect the number. I am in Colorado and we have 20% less air so 20% lower number.
john |
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02-20-2025, 10:40 AM
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![3.6 Cayenne 958 Compression test results, ok? [I know its not a 911 lol]](http://forums.pelicanparts.com/iconimages/911-engine-rebuilding-forum/3-6-cayenne-958-compression-test-results-ok-i-know-its-not-911-lol_ltr.gif)
