128 - 140 compression in 911sc - due to lack of use?
 

I just had a PPI done on a 1980 911sc targa with a legit 43k on the clock, and the compression ratings with the throttle closed were 128 to 140.

The general mechanic in the very, very small town I had it done thought it could be because the car was used for several mile trips to town and then would sit for long periods, causing buildup from fuel sitting in the cylinders unburned which would reduce the amount of oil and hence the compression.

He thought that if I just drove the car the build up would burn off and the compression would rise.

Could this be true?

Or could I be facing a rebuild even though the car has so few miles, has enjoyed regular service, but just hasn't been ran?

I'd have a leakdown test done.

It could be just build up and washed the ringlands a little. With the oil pressure up and "clearing out the cobwebs" via a nice spirited drive then you could recheck it. I bought a used motorset out of a Nissan Silvia with 35k but hasnt turned on since 95 when the car was totaled. The numbers varied by 20 or so but were barely within spec acroos the board. Did a wet leak down test and it showed ok, then after driving it for a weekend I recheck and the numbers were only off by 5 +/-.

Throttle closed? Compression tests are generally done with the throttle wide open. Was the test done with the engine warm?


JR

Yup. Engine warm, throttle open. If the engine has not seen much use in recent years, drive the piss out of this car for a while, and then do the compression check. Leakdown test follows, if all six cylinders are not within about 5% of each other. My guess is that this engine is just fine. A better compression test will show pressures in the 160-165 neighborhood. Or maybe 185-190. I forget whether 1980's had 8.6:1 CR or 9.3:1 CR.

throttle open on individual intakes like carbs or MFI, doesn't matter on common plenum intakes like SCs and carreras. warm and well oiled rings, crank until the gauge tops out, not 5 rotations or so. more like 10-12. cold and been sitting a long time, you get lower and inconsistant readings.

Called an "Italian tune-up". :)

Thanks for your help, guys, especially those of you who very generously responded to both this thread and to my earlier thread, asking for general opinion on the pics and description of the Hellblau 911SC down in Kentucky.

I'm inclined to believe the gent I'm buying this thing from. He's a well regarded deacon in the local church (as described by several unrelated folks I spoke to during my search for a proper mechanic) and he just seems too genuine to be a phony. If he were in brooklyn, that's another story.

I think buying this thing for $10k, shipping it up for another $1k and investing $1 or $2k into lines and hoses and what not will turn the car from a neglected garage queen into a road king.

Naturally, any other opinions welcome. Much obliged. -Adam

That's sorta funny.

So is "Italian Tuneup".

Count the head stud nuts. There should be 24.