MSTv2 Woosh

[b58.noa]

So, these cars from what I hear have no blow off valve, or recirc valve. I'm stumped, because months ago after adding an MST it vents pressure after letting off the throttle. Where is the woosh coming from? I know it can send pressure through the cylinders, but I figured that noise was the brap when shifting at high rpm.

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[BumbleBoi]

So, these cars from what I hear have no blow off valve, or recirc valve. I'm stumped, because months ago after adding an MST it vents pressure after letting off the throttle. Where is the woosh coming from? I know it can send pressure through the cylinders, but I figured that noise was the brap when shifting at high rpm.

It's air coming back out via the filter.
You can hear the same woosh sound when lifting off throttle in a non turbo car.
Just due due to differential pressure when the charge pipe and plenum has higher pressure than atmospheric.