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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N55 Turbo Engine Tuning and Exhaust Modifications - 335i Tuning > Turbo Spooling sound and after letting the accelerator go



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      09-19-2016, 01:00 PM   #1
BRAISKI
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Question Turbo Spooling sound and after letting the accelerator go

I have an intake in my car and some friends ask me whats the sound and why... I am not as knowledgeable about turbos as I'd like. I would prefer to give the right answer rather than pretending

I understand the spooling part but what do you call the sound (blow off sound) after you shift gears or release the accelerator? Why does it do this? To release excess air?
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      09-19-2016, 01:19 PM   #2
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That's the diverter valve.

When you let off the gas, the throttle closes, but the turbo is still spooled up and making boost, trying to push compressed air into the engine.

Since the throttle's closed, there's nowhere for all the boost to go. The diverter valve recycles the compressed air back into the intake before the turbo.

(A blowoff valve does the same basic thing but vents the air to the atmosphere.)
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      09-19-2016, 01:41 PM   #3
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Quote:
Originally Posted by AtlasM View Post
That's the diverter valve.

When you let off the gas, the throttle closes, but the turbo is still spooled up and making boost, trying to push compressed air into the engine.

Since the throttle's closed, there's nowhere for all the boost to go. The diverter valve recycles the compressed air back into the intake before the turbo.

(A blowoff valve does the same basic thing but vents the air to the atmosphere.)
Awesome thanks!!!

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