sootie
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...releasing Boost pressure.
Ithought that's turbo surge when boost is going back out[/QUOTE
not sure what you mean but that sound being explained is what most people call "turbo bark". When you let off the throttle suddenly, the vanes on the vgt open. already boosted air almost instantly has no more drive pressure forcing it into the engine therefore follows the path of least resistance. essentially, the air is trying to turn the turbos backwards as it escapes back thru the air intake. hence the reason it is so hard on thrust bearings and turbo shafts due to shock.
same thing can happen on large non-vgt setups when there is a drastic change in rpms for example when the tc locks. hope this helps...
I know what "turbo bark"/surge is. But he's talking about that BOV sound when you let off. I was told it's the vgt vanes relaxing and that's the sound of exhaust pressure going through the vgt housing
Reading back he could either be talking about turbo surge or the sound made when you let off the throttle and and its sound like a whooshing aound