12-21-2011, 12:41 AM | #1 |
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Butterfly valve - 650i MSport exhaust
Featured on BIMMERPOST.com 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: |
12-26-2011, 07:54 AM | #3 |
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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, 04:46 PM | #4 | |
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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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