agent325

I had a PPI done on a 968 i'm thinking of buying. The shop that inspected the car said it had good compression all the way around at 135 Lbs. Not sure what measure is used to check compression. I tell my mechanic back in LA that compression is at 135 and he tells me its low. he tells my compression should be higher on 968s at around 175.

Its there two ways to measure compression, or is 135 low?

agent325

anyone...help?

trebor_quitman

I believe the 968 compression ratio is 11:1, and I think one BAR is ~14.5. So that gives you ~160. Sounds like 175 is abit high, but since I've never done mine, I don't know what I'm talking about, so I can't say for sure what it should be. I've got the shop manuals at home, I'll see if it is listed there.

Alex Cook

agent 325,

I had a compression test done when I bought mine last year - came out at 220psi for the #1 and #3 cylinders, and 215psi for the #2 and #4 cylinders.

Unfortunately, being a mechanical ignoramus I can't offer any insight into what these mean - but I was told at the time that this was a good result.

Good luck with your purchase - hope it works out.

Magnus

135 sounds low... I did a test on my 944 '83 (euro with 160000 km on the clock) and got around 14-14.5 bar = 203-210 psi.

//Magnus

trebor_quitman

I'm sure someone in the know will post, what is the flaw in my logic above? What is my math not taking into account? Thanks

agent325

They car checked out great with a clean car fax, but the compression is what worries me

PorscheG96

Those are VERY HIGH and VERY EVEN numbers, you should be pleased.

My 86 944 has 9.5:1 compression [?] and had 162 psi across the board with 90k miles.

At 11:1 compression the 968 should have compression values above 185 psi, I think.

I would have another shop or mechanic do the compression test again. I haven't done the test myself but there can be significant differences with a hot/cold engine and doing the test with the throttle open/closed.

Good luck!

Dmitry S.

Yeah, my 1982 924 has 160psi across the board, and that's with 9.0:1, so those numbers are REALLY low.

trebor_quitman

Bump;
Can someone help me out? From the numbers people are listing my logic is flawed somehow. I'm just curious as to what I'm missing. Thanks,

Jfrahm

I think a lot has to do with how cold the engine is. If the air is being heated as well as compressed the pressure will spike up more (like with an engine that has warm heads as opposed to one that is dead cold.)

Gauges vary quite a bit too. I would not get worried if the numbers seem somewhat high or low, as long as they are pretty even.

-Joel.

rsrdan

http://www.csgnetwork.com/compcalc.html

Try this formula!