Craig W.

I had similar leak down numbers on the pristine 49k mile street '91 C2 I bought to hack into a full blown track car. It was also driven very little in its last couple of years. My mechanic said he'd charge me about 2k for a top end job. I told the PO this, and we took the 2k off the purchase price.

Well, I should add that the number were similar, but one of the cylinders was over 30%.

My wrench, a respected engine builder, said go ahead and run it, worst case we go ahead and do the top end.

I drove the crap out of that car on the track for a few years, learing to drive and eventully winning a bit with a "gimped motor". I ended up selling it without ever doing a top end.

Not saying you should buy that car. I'm saying take the top end work off the price, drive it hard, and you might never end up doing the work.

Yes, I do wonder if that car would have been faster with a new top end, ;p

Kevin

Hear is another point of view.. There are alot of cars out there. Leak down numbers greater than 15% does indicate that compression in the cylinder is passing through the valve train or rings.. or alot of carbon build up. The range between #2 and #3 is a little to much for my money. Rule of thumb is no more than 5% range between the numbers. If the car checks out in all the other areas. I'd run some techron through it and put some miles on it.. See if it improves..

traveller09

Run!

Mine was 1-2% across the board. I passed on a low mileage 91 that had 2 cylinders that came back at 16 and 18%, the best one was only 8%. A mechanic told me the same thing about the Techron, I asked a few well respected mechanics and long time 911 owners that I trusted and they all said run there are plenty more out there. Also, the car was across the country from me and not worth trying to figure it out. This is where the advice “don’t fall in love with the car” comes in handy. You find the car you like and you don’t really want to walk away from it.

I feel for you, good luck.

pjc

Why bother to worry if the readings are right or wrong - you will always have that doubt in your mind so walk away, there's plenty more 993s out there to look at its just a question of waiting for the right one.

PJC

Peter Zimmermann

My two cents worth: This test should be done on a cold/cool engine, which will make the test easier to perform. Readings at 10% or less are acceptable, with 3 - 6% the norm. Bad readings usually occur when the test is not done right. The engine must be turned by hand to TDC for the cylinder being tested - BEFORE that cylinder's spark plug is removed. If not, carbon can be trapped between the exhaust valve and its valve seat, which will allow air to escape, producing leakage. I have done hundreds of leakdown tests in this manner and have never had a false reading, if I got a 50% number the engine had a problem. I've had 911s brought to me for a 2nd opinion, following a troublesome leakdown test done by others, and 99% of the time got perfectly acceptable numbers (a short drive will blow out those pesky carbon bits on the exhaust valve seat). No day at Willow or Road America is needed! Those carbon pieces are precisely why compression tests on 911s are not recommended - that test requires that all 6 plugs be removed before the test is performed. Best of luck!