cunno

Look for some help here, I have a 997.1 GT3 with a 3.8 conversion and modded cams. It was making 475bhp and 350 ft lbs of torque until the cats decided to let go and get sucked back into the engine. End result we had to strip engine again and installed new pistons and liners, heads and values were checked and reseated. But this time round the power isn't there 430 Bhp and 315 ft lb torque. Done leek down test 2-3% and a compression test 140psi. Now this seems low but we also tested a standard car with 30k miles and that was running 145psi. Now according to porsche the compression ratio is 12.2/1 therefore 180psi.

So the question is has anyone with a 3.8 GT3 or RS done a compression test and what results did they get.

Also has anyone had the vario cam activater fail and does it flag a fault code?
My engine runs very smooth and apart from missing the extra power you wouldn't know there is something wrong. Any advise in finding vault would be appreciated

Jon

Spyerx

when i had my car compression tested and leaked down (3.6RS with 40k miles, a solid amount of track days) the compression was 180+ and leak less than 1% on all cylinders.

Macster

Did you "cc" the combustion chambers to confirm they were the right size? What about the height of the pistons? Are the pistons the right ones for the engine?

During a compression check the throttle valve is closed. Not completely shut it has a small air gap but the gap is pretty, well, small. You might need to remove the throttle body to eliminate any restriction to air flowing into the engine.

Even if this improves the compression numbers the throttle valve's small gap is not a factor when dyno testing the engine.

Another source of lower compression is valve timing. However, my limited experience in this case is the engine doesn't run well at low RPM. Still, it can't be dismissed.

I had what proved to be a VarioCam solenoid/actuator fail in my 2002 Boxster. The engine's idle was very up and down. There was no CEL but there was a pending error code: P1341.

The low compression numbers I believe don't appear to arise from a failed VarioCam solenoid/actuator. And because all cylinders are down it would have to be a double failure.

Thus my WAG is the engine doesn't have the compression ratio is should have.

cunno

Thanks for the input gents, all parts are Porsche 3.8 RS with new Con rods to allow for the 23mm pins. Yes I had simpler conversation with my guy whether the cc was correct and 100% sure they are 3.8 bits. Only checked compression with engine in car with psi gauge so this is why we checked against a standard car for reference. Spyerx was your engine checked in car? Very good results.

Macster thanks for the advise, we checked timing twice now, and the car runs so smooth, cars going in on Thursday for a second compression and leak down test as we done some more running in. Agree a double fault in the variocam system would be odd and would it effect the torque?

Spyerx

yes, LD / compression were checked while engine was in car.

Tom@TPC Racing

One idea is to check the vacuum-operated actuator behind the intake manifold. If the flap is not opening then maximum top end power will not be achieved, like having a smaller volume intake manifold on the engine.





The vaccum hose goes under the intake manifold to the top solenoid next to the alternator. Also check the vacuum hose from the source to the solenoid and the electrical connector that triggers the opening.

Spyerx

I believe this can be actuated via PIWIS / Durametric to test.

cunno

Thanks for the advice gents will get these checked on Thursday while have the second compression test done.