p951guy

does anyone know if these numbers are good for leakdown test

cylinder 1= 10%
2= 9%
3= 10%
4= 8%


compression across all 4 cylinders was between 120-115

are these good numbers. the motor is running very well

thanks

aka 951

nope - should be 150 on all four or pretty darn close

MAS

Yeah... my 87 924S when tested at the Porsche dealer a few months back was: 175/170/175/170

-MAS

Steve Lavigne

I got 4% leakdown all across on my 107k motor, though the head was replaced 3k prior.

'86 951
-Steve

p951guy

are you serious? how bad are the numbers? the car still puts out over 285hp and pulls very hard. how could those be bad numbers? at what point is it time for a rebuild?

Andre

how much does it usually cost ot get a leakdown and compression test?

p951guy

my car only has 84,000 miles on it.... what could cause these numbers to be so low? is it possible the guy did the test wrong?

MAS

Hey, it sounds to me like your numbers may be wrong. I'd go get another compression test done... any garage/mechanic can do it in a few minutes.

-MAS

p951guy

Thank you MAS. i was about to have a heart attack. My car only has 84,000 miles on it and blows away everything i've ever raced including several corvettes and several other porsches including my bosses 1999 carrera. does that sound to you like a motor that is just about dead? i sure hope the numbers are just wrong... you said any shop you could it.. i'll take care of that monday. thanks again

Dave

The 170-175 that MAS quoted is from a motor with higher compression, a turbo will not create this much pressure. I'm far from being an expert, but I've always heard that leakdown up to 10% or so is OK. I've also heard that 140-150 is "normal" for a turbo, as AKA951 said, but I don't know what is considered "bad".
As long as it's running "very well", there may be no need to do anything yet (unless you have a bunch of cash to get rid of), also keep in mind it may just be the head as opposed to the whole engine.

keith

I think anything over 125 (and very close between cylinders) is good for a mileaged 951.

That is entirely my opinion, however.

Make sure the vehicle is at operating temp, and perform the leakdown with ALL the plugs removed and WOT.

Anyone agree/disagree with this procedure?

Steve Lavigne

I did the leakdown test myself. Before I bought the car I had a knowledgeable shop do a PPI. They told me it was 125 all across (this was after head replacement) and said that was good. I imagine it might depend on how many times they let it crank over for the compression test. In the factory manual it lists something like 150 as the optimum spec.

I suppose that with all the plumbing installed you would get significantly different numbers than with just the long block. When doing a compression test, you could try opening the throttle body and maybe even disconnecting the boot to the throttle body so that the air isn't going through the stalled turbo.

Maybe someone else who actually knows could comment on this.

Steve Lavigne

That sounds good to me. I would say that having the engine warmed up and well oiled is very significant. I don't think WOT really matters for a leakdown test since there should be very little air actually getting past the intake valve seat. The most critical thing about a leakdown test is making sure that the engine is at tdc so that your breaker bar doesn't become a big bat when you put 100psi into the cylinder.

After reading over your post, it looks like you may have meant compression rather than leakdown. If that's the case, ignore what I said.

Mike B

Optimium compression numbers = compression ratio (8.0 for a 951) multiplied by 18-19.

8.0 x 18/19 = between 144 and 152.

I just did a test on the 951 motor I am about to drop yesterday...100, 100, 100 & 80...eeek...I even did it wet (with oil) which caused the numbers to rise idicating a ring problem...

keith

Buh - you're right - I meant COMPRESSION TEST, not leakdown...