rcropp1

I had a compression test done as part of a PPI. The car has 68k miles.

The number case back:

Cylinder #1 182psi

Cylinder #2 180psi

Cylinder #3 185psi

Cylinder #4 185psi

Cylinder #5 187psi

Cylinder #6 181psi

Should I have concerns with any of these numbers? Thanks. Robb

Gbos1

205 - 215 is sometimes seen as Normal..... Seems lower than Normal but these numbers don't really matter much to me. There are a number of reasons why the numbers can vary. What are your Leakdown %s per Cylinder? These matter.

rcropp1

The PPI was done as a Porsche Dealer. A leakdown wasn't done as the service tech determined that because the compression numbers were high and closely grouped no leak down was needed.

Gbos1

yeah ok .... Compression Test means very little ... Leak Down Test is CRITICAL when purchasing a Air Cooled 911. I WOULD NOT PURCHASE AN AIR COOLED 993 without a Leakdown Test on each Cylinder. Leak down Test will give a better picture of engine health. Porsche Dealer or Not. Apparently your dealer isn't very "Knowledgeable" about Air Cooled 993s. Never trust the "Stealer" They are in it for themselves.... Steve Weiner feel free to weigh in here. ........... An engine rebuild is easily $12K - $18K+ ....."While you are in there" can get quite expensive.

inkatouring

So, I'm not as absolutist as Gbos1, but in general a leakdown test is better than a compression test for these cars. Here's a recent thread about leakdown from my recent purchase. There's a a lot of noise in the thread and opinions by those who have lots of confidence in their opinions but less experience.

Gbos1 is right, Steve Weiner of Rennsport Systems is the best person to listen to in this area. While I talked with him about leakdown numbers, the same holds true for compression: you're ideally looking for a close grouping and you certain have that. The raw numbers appear a tad low, but not horribly--and there are various reasons for low numbers.

Something to keep in mind, as discussed in my linked thread, is that too many of these cars have a valve guide problem and it can be very expensive to fix if they haven't already been replaced. Whether you actually will replace them is one thing but it's very common for them to prematurely wear. My car burns oil at about a quart every 1-2k miles (I think, time will tell) and I'm sure it's through the guides. Is that enough to bite the bullet? No for me right now, but some day.....?

Churchill

The tech is right. Those are great compression numbers and I wouldn't bother with a leakdown. An LD won't tell you anything about the valve guides. It is for pinpointing the source of poor compression (i.e. rings, intake or exhaust valves). If the car is using a quart+ of oil in between changes, eventually it'll need guides. Almost every one of them does.

Gbos1

Really? I guess Steve doesn't know what he is talking about ..............


https://rennlist.com/forums/993-foru...r-smoking.html

Churchill

I've known Steve for 20 years and have also performed more than a few compression and LD tests. I think Steve would agree with the following: on a low-mileage engine that you have no reason to believe is unhealthy, a compression test is step one. If results are good, you're done. If results are not good, you use LD to confirm and locate the source of the problem. If you're testing an engine with high miles, you're justified in doing both from the start.

This approach has never let me down.

mpruden

For what it's worth, Churchill isn't the only engine mechanic that recommends starting with a compression check, then moving on to leakdown when there is evidence of a problem. Bob Grigsby with 45yrs experience recommends the same thing. I'm not sure he would say it with all caps though, so it may not have the same authority when read on an internet forum.

For an alternate way to access the health of the SAI system, with the car off, you could ask the dealership to force on the SAI pump at the relay, then monitor the O2 sensors for the expected rush of air using their Porsche tester. They should be very familiar with reading O2 sensor info and could compare the numbers between the banks.