Cor2nir

Hi I just got a PPI and Compression check on a 1996 C4S. The car has low miles under 30k and I got the compression results back and wanted to make sure that they are good results. 1-6 Cyclinders had a 200. I know in some cars consistency is the key for compression and this is obviously very consistent as they are the same for each cyclinder. Let me know what you guys think.


Corey

kkim

I think the rule of thumb is up to 10% (or is it 10lbs???) diff between max and min is acceptable. In any case, I believe 200 is a good compression number, but am kind of suspicious that all read right at 200? Seems highly unlikely that all the numbers would be exactly the same.

Speed or fly yellow?

edit... added this thread... https://rennlist.com/forums/showthre...mpression+test

vjd3

911's are usually 170-180 for a healthy number ... Turbos are lower, obviously. The 200s seem kind of weird to me, too.

Bull

I don't think I can remember a test showing exact numbers for all 6 cylinders. 1-6 at 200 even would cause me to get another test....elsewhere.

kkim

That's what I thought after reading his post, but after doing a search (imagine that) and reading a comment by Chris W that it is not that uncommon for 993s to have 6 exact cylinder readings, I don't know. I do think the 200 number is a bit outside the normal 993 range, which kind of leads me to think a compression test was never really done.

chris walrod

200 does seem on the high side (not a bad thing if its accurate). My car was 185psi exactly across all 6. I questioned the guage at the time as well. I thought it was a bit odd..

Bull

It is good to learn something new every day!

Cor2nir

Guys thanks for all your responses I am not sure what to do as it does sound good 200 compression across the board.

Chris,
How many miles were on your car when you had this done? This car has under 30k miles and has been babied not been to the track or anything.

I also had a PPI done on this car and they came up with a few things that need to be done as well but they said Compression perfect and I asked them what they thought of it and they said it is a well taken care of car so the number should be high.

Let me know what you guys think.

Corey

Bull

I just looked back at my records and my cars test at 14k was all 185s and 187s.

chris walrod

Many feel leakdown results are more indicative to the condition of a given engine vs. compression results. I would tend to think a tracked car would present better leakdown numbers than that of a car that has been babied, ie never had an Italian tune-up.

My car has 40K miles at the time and was a babied car. After a few track events, the car seemed to run better. Smoother idle, improved throttle response.

cowtown

Keep in mind that cyl. compression has a lot of variables - engine hot or cold, how fast the battery was cranking the starter, whether they happened to put a little oil in the pots first, etc. It's the variation across cylinders that's interesting. Yours sounds good, assuming their gauge was off but measuring consistently. Just for comparison, my 993 had 180-185 across all 6 when PPIed. My old '88 3.2 Carrera was around 140-145. My 3.0 930 motor (6.0-to-1 compression!) is sub-100 lbs.

Pedro356C

Chris is 100% right and I think the Porsche gods made these babies like this...if you want a lousy car, treat your Porsche as a garage queen...want a great car...drive it frequently...bring it close to red line once every single ride...don't hold the horses or they will be crippled by the lack of exercise.

My 1965 356 was just like this...sometime I had to stay overseas for a couple of weeks and I got used to find "crap for car" when I got back...after a good 60 miles drive with some gear shifting close to 5k rpm, the car was back to life...breathing free and happy again...

Part of the Porsche soul I guess...respect them and drive'em frequently and they will never let you down...even if they have to brake down, they will do so in front of your house...these cars reciprocate love!!! Am I sounding a bit crazy here?

cooz

if the engine idles and runs good and you have no engine light on.....then all is well regardless of the exact compression readings. if I needed to know further, i would have someone else do another test as i suspect first test not accurate.

norm
95 C2

TheOtherEric

I don't think 200 is particularly high. My first 993, which I watched getting a compression test, measured up to 240psi on one cylinder. It had up to 10% cylinder-to-cylinder variation, which might help explain why that car was a dog.