I was wondering if anyone can answer a question for me. I did a compression test on my 993 Cup car today, the results are as follows.
1)178 psi
2)183 psi
3)183 psi
4)180 psi
5)180 psi
6)190 psi
Does anyone know if these are good numbers?

I than did a leak down, again here are the results
1)12%
2)12%
3)12%
4)12%
5)12%
6)18%

My question is what do you make of the compression numbers, leak down numbers and why is the cyl (6) the one with the best compression have the largest percentage of leak down?

 

Did you do the leakdown with the engine warm?

 

Those are pretty high leakdown numbers. I dont know about a supercups, but for turbo engines that is not good at all.

My current leakdown is 0% on 5 cylinders and 1% on 1 cylinder.

My compression numbers since it is a turbo (ie... lower compression) are 135.

Norm

 

High leakdown numbers.

 

what yr? mileage? how does can run? what did tech say?

higher mileage engine could have leakage figures that high...
leakage readings may not be accurate....
all readings of both compression & leakage are consistant without much variation....

i would guess this engine runs well...does it?

cooz
95 C2 with 100K miles

 

The engine was stone cold when test were done. It seems to run fine, but at the Glen race the other 993 Cup could pull me.

 

Russ,

It sounds like it is definitely time for a rebuild. IMO I dont like seeing numbers above 5%.

When the leakdown was done, where was it leaking ? Intake valves, exhaust valves, or rings ?
You can tell by where the pressure is escaping. I would guess you have bent valves - BTDT...

Norm

 

I'd repeat your leakdown test with the engine warm and I'd imagine that they will come into line with what you'd expect (3-8% leakdown depending on # of hours). In reference to other cup cars pulling you down the straight, engine output is significantly impacted by whether or not the engine has been built to factory published specifications (blueprinted). For instance, the 964 Cup cars (or any C2 for that matter) have an advertised compression ratio of 11.3:1, but when measured from the factory, they end up to be 10.4-10.7:1 compression. So when rebuilding them to CTC-1 rules, you can set them to be 11.3:1 compression. This along with all of the other tolerances that are checked are why some 964 Cup cars (blueprinted ones) are stronger than others, on the order of 25-35hp more. The Mahle Motorsports pistons tend to better match the advertised ratio, but I'm not sure if the 3.8l Cup engine has the Euro RS 3.8l slip in P&C (Street) or the 3.8l RSR bore in P&Cs (Motorsport).