930 compression & leakdown #'s

plastix · 03-30-2005, 04:22 PM

What are acceptable compression and leakdown numbers on a 930? I'm looking at a car from 1987, with 67K stock miles (supposedly never been apart). Car looks and drives great. However, the PPI showed compression #'s in the 80/85/90 range, and leakdown percentages from 10-12%. I'm a newbie, so pardon my ignorance: but aren't those numbers indicative of a tired motor? Shouldn't the compression numbers be in the low 100's? Ideally, wouldn't the leakdown numbers be in the <10% range?

The out-of-state shop that did the PPI (happens to be where the owner bought his car and gets his servicing done--but also a shop that has been recommended by PCA members in that region) claims that these numbers are "spot on" and "very tight." But everything else I've heard says otherwise. What am I missing?

Grady Clay · 03-30-2005, 05:02 PM

Welcome to the Forum.

Based on my experience, those are low cranking compression and high cylinder leak numbers. That said, it depends on the gauges and circumstances. If the shop regularly checks good engines and these are comparable numbers – then OK. For my $, I would put some highway miles and “spirited” driving on it and re-test. It would be useful to have someone independent of the owner and prior work to do the testing.

I am of the opinion that if you find what you think is the “right” 911 (930) for you, you can’t do too much PPI.

Best,
Grady

dean · 03-30-2005, 05:27 PM

My 930 has leakdowns of 1 to 2.5%. I also agree with Grady about the #'s.

Also I don't care that the PCA recomended the shop. Find another one that isn't biased for the PPI.

Dean

trader220 · 03-30-2005, 05:41 PM

When I was looking at 930's those are numbers I walked away from. Where is the car located? I am sure there are people on this board that can reco a shop in the area.

MobileWrks · 03-30-2005, 06:26 PM

Tell the shop you want a LEAK DOWN. maybe their gauges read low. But to me 930 are above the 100 range. Maybe they are doing a compression test and not giving it full trottle!! That would be my first bet. If they dont know how to do a comp,why have them do a ppi... do like trader and dean say,post a PPI IN ??? on the main page,youll have alot of pelicans willing to help you..... GOOD LUCK !!!!!

john walker's workshop · 03-30-2005, 06:45 PM

i did a 86 930 yesterday that pumped 125 average. they do have low compression, compared to a regular carrera. does it have nasty cams with lots of overlap? 4% leakage is considered very good, so that one is kind of high, but maybe it's all carboned up and needs to be driven hard for a while, or maybe they didn't run it after loosening the plugs, and got carbon bits caught between valves and seats. have another shop re-do the tests if you like the car enough. results vary between gauges, and cranking speed can affect compression test results.

JTL · JTL's Garage

Just tested a friend's newly rebuilt -89 3.3L turbo. All cylinders showed exactly 130 compression. I really enjoyed the rebuild and finally learned how to time the cams.

jt

plastix · 03-31-2005, 05:59 AM

Thanks for the replies. Your skepticism matches what I've been feeling. The test was performed in Reno, NV. I've been told that the altitude there is about 4000+ feet. Anyone know if this could explain the differences?

hobieboy · 03-31-2005, 06:10 AM

Leak down should be altitude in my understanding.
Mine ranges from 2-6%. Above 10% does sound high to me but like John said, it could also be carbon stuck between valve seats.