Greetings all. I've had a 2001 TTQR for a few years now and have just started modding. I have been lurking for a while though.

There is a thread currently open on boost machine DIY (I think). There was a debate in there about exhaust cutouts and high boost under open exhaust conditions. As a former DSMer I have dealt with this issue quite a bit. It's called boost creep. I assume it's the same in these cars even though the N75 valve is electronic where DSMs have "passive" wastegate control. The problem is in wastegate flow. As the wastegate opens it diverts exhaust gas from the turbine side of the turbo. Thisdamps the positive feedback cycle and limits boost. After the wastegate those diverted gases need to be routed back in to the exhaust pipe and out the back. If you increase the size of the exhaust pipe both the primary and diverted gases will flow better once they are recombined. The problem is that you still have the original diameter between the wastegate and downpipe. Now when the wastegate opens there is less resistance for the gases to go across the turbine, but the same resistance as before through the wastegate. You will get less gas diverted therefore more boost and less control over the boost level.

I hope that wasn't too convoluted or already covered somewhere else.

Have a great day
-Zelpdsm

 

The problem was with a A4 with a gt35r and im guessing a tial 38mm wastegate. That has been enough for the others that have run the same turbo and same boost ranges as him.

 

Strange. Did they have wide open exhuast? I would thinka 38mmwastegate would solve it pretty quick as long as it's plumbed properly.

 

i dont know the facts but i believe Ray said he had a 2.75" exhaust and a 3" dump and i would assume the tial was dumping and not put through the exhaust.