8 minute video so dial-up beware.

http://video.google.com/videoplay?docid=63...2&q=Audi+S2

At one point you see the shift light come on at 'round 9300rpm but he just takes it to 10K Kinda cool near the end when you hear the pop-offs fluttering on the track and just how quickly this thing accelerates.

WICKED!!!

What is that high pitched fluttering sound when get gets off the gas?

Turbo waste gate....releasing excess turbo boost on deceleration.

kinda sorta

Wastegate limits boost, bleeds off boost at a set level (though sometimes adjustable from in the cockpit)

The flutter you hear when the Audi is off the gas are the blow off valves. These prevent the turbine from suddenly stalling when the throttle plate is closed. They prevent breaking fins off the turbine, that would result from the turbine stalling when the throttle is closed.

On street cars, ie stock turbo cars, they plumb the blown off boost back into the system. On race cars, and on many modified ricers the blow off is just dumped into the atmosphere for everyones audio enjoyment

That would be the blow off valve. It opens under engine vaccum conditions to keep the intake charge from bouncing off the closed throttle plates and destroying the thrust bearings on the turbo. Plus it keeps the turbo spinning between shifts and on/off throttle conditions to reduce lag.

The wastegate controls boost pressure. It has nothing to do with decelaration.