If I understand correctly, the stock turbos in these cars use an oil hydrostatic bearing and the oil pressure is supplied by the engine oil pump. When you come to a stop and shut down the engine the oil pump stops but the turbo is still spinning. What allows it to spin down safely as the oil pressure drops to zero?

It doesn't spin for too long worry about,there is still a cushion of oil that it sits in,it is still a good idea to let the engine cool a bit before turning it off.

...there is no load on the turbo when the engine is off. any oil left is enough for it to spin down safely

hth

That's sort of what I mean't.

If you take a look at the egt when you come to a stop,and when the EGT is at it's lowest temp,then that's a safe time shut it down,sometimes in my Dodge it take a couple minutes if I've been pulling a load.I haven't had my Audi long enough to see yet,but I doubt that it runs as hot as my diesel for as long as the Dodge does,45 psi of boost has a nasty habit of doing that.

after you come to a stop to allow the turbo to spool down?

This was first suggested to me by a heavy duty diesel mechanic, who suggested to allow the engine to cool after stopping and before shutting off the engine. On follow up it was to allow the turbo to spool down. (he was quite impressed by the car, I let him take it for a spin in the rain)

If you do ... how long do you leave the car runnning before shutting it off? A few seconds? 10 - 20 - 30 ... a few minutes?

just curious

thanks

jeff

supplies water to cool down turbo after you shut it off.

normally when I shut down the car I am at idle, therefore the turbo is already spinning as slow as it is going to.

Cool down is somewhat different, but unless you have really been beating on it such as a track day there really is no need for cool down with these cars as the after run pump provides circulated coolant to the turbo after you turn the car off if it is necessary and keeps it circulating until the turbo is within normal parameters in terms of temp before it shuts off.

The turbo is both oil and water cooled in the UrS.