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      12-21-2011, 02:41 AM   #1
roadsta
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Thumbs up Butterfly valve - 650i MSport exhaust

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There is a vacuum-actuated butterfly valve in one of the two exhaust openings on each side.

I think this is what makes that delightful sound in sport mode when the gearbox shifts up. (In another thread someone called it a 'booming sound')

It sounds open on a cold start too. When else does it open?

A few (poor) photos of the valve and the actuator:
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      12-22-2011, 03:59 AM   #2
Soorena
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Get rid of it
if it's like other BMW's, it should open at 3500rpm.
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      12-26-2011, 09:54 AM   #3
E90Fleet
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Its actually there to make the exhaust sound less "boomy" at low RPM
It will open at higher RPM.

Its there to make the car quieter`at low RPM
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      12-26-2011, 06:46 PM   #4
roadsta
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Quote:
Originally Posted by E90Fleet View Post
Its actually there to make the exhaust sound less "boomy" at low RPM
It will open at higher RPM.

Its there to make the car quieter`at low RPM
Thank you / Dankie.

This makes sense.

Also, on the cold start, I was wrong. I had a look the other day, the butterfly does not open. The exhaust probably just sounds noisier becuase of the higher engine revs at cold idle.

roadsta
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