2004 Turbo boost curve
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Joined: Aug 2001
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From: Hudson Valley
2004 Turbo boost curve
I recently did work on my 2004 Cayenne Turbo which included valve cover gaskets, spark plugs, etc. In doing that job, I came across some "creative" engineeering, which I repaired properly... I also was around some of the (very brittle) hard plastic vacuum lines.
After wrapping up the job, a brake master warning lamp came on, which did go out before returning. I did some googling and suspected the mess of hoses and check valve behind the right side SAI pump, but all seems well there per the smoke test. Following a WOT run 100 miles from home, the car was unable to build boost and shifted poorly. The first thing I did was smoke test the intake, which revealed a substantial leak from the front. My dealer only serviced 955 had 5/8 heater hose cobbed between the PCV and the driver side oil vent from the turbo. As in..not even connected. I also noticed the turbo inlet boot was very very loose. Interestingly, there was no check engine light, but a code scan revealed some lean at idle etc codes.
Anyway, all that was buttoned up, the only leak I have after smoke testing now is out of the left side variocam solenoid seal in the valve cover. Never would have guessed. While I still have the brake booster warning, all drivability is restored and there is no smoke escaping anywhere else.
My question is, what is the real world boost curve like on a Cayenne? According to Porsche documentation, .6 bar should be reached at 2250 rpm, where it reduces to .5 bar till redline. My car, with these leaks fixed is making very little boost until 2800 rpms, where it reaches .4 till almost 4K rpms when it hits hard, pegging the gauge at .8 bar, eventually dropping to .6/.7 at redline. Obvioulsy, this makes it fun to drive (almost reminds me of my big turbo 951 the way it hits at 4K rpm) but I do feel it should be making boost sooner. I want to say the car used to peak at .6 bar, but built boost instantly. Maybe just the more moderate peak boost made the off boost contrast less obvious?
Also, does this behavior seem indicative of a tune? The previous owner was a PCA member and this car was generally very well taken care of.. Is there anyway to check?
Thanks
Mike
After wrapping up the job, a brake master warning lamp came on, which did go out before returning. I did some googling and suspected the mess of hoses and check valve behind the right side SAI pump, but all seems well there per the smoke test. Following a WOT run 100 miles from home, the car was unable to build boost and shifted poorly. The first thing I did was smoke test the intake, which revealed a substantial leak from the front. My dealer only serviced 955 had 5/8 heater hose cobbed between the PCV and the driver side oil vent from the turbo. As in..not even connected. I also noticed the turbo inlet boot was very very loose. Interestingly, there was no check engine light, but a code scan revealed some lean at idle etc codes.
Anyway, all that was buttoned up, the only leak I have after smoke testing now is out of the left side variocam solenoid seal in the valve cover. Never would have guessed. While I still have the brake booster warning, all drivability is restored and there is no smoke escaping anywhere else.
My question is, what is the real world boost curve like on a Cayenne? According to Porsche documentation, .6 bar should be reached at 2250 rpm, where it reduces to .5 bar till redline. My car, with these leaks fixed is making very little boost until 2800 rpms, where it reaches .4 till almost 4K rpms when it hits hard, pegging the gauge at .8 bar, eventually dropping to .6/.7 at redline. Obvioulsy, this makes it fun to drive (almost reminds me of my big turbo 951 the way it hits at 4K rpm) but I do feel it should be making boost sooner. I want to say the car used to peak at .6 bar, but built boost instantly. Maybe just the more moderate peak boost made the off boost contrast less obvious?
Also, does this behavior seem indicative of a tune? The previous owner was a PCA member and this car was generally very well taken care of.. Is there anyway to check?
Thanks
Mike
