BMW 3-Series E46 (1998 - 2005) - 99 328i exhaust flap

Honest John Back Room » Technical matters
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Sun 6 Apr 2008 10:34
99 328i exhaust flap - x332race
There is a flap in one of the twin tail pipes on my 1999 328i. I understand that the flap should be closed at low revs and open up at higher revs. The flap on my car is stuck in the open position. Will this affect the performance / driveability of my car in any way?

Edited by Pugugly on 06/04/2008 at 11:03

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Sun 6 Apr 2008 19:44
99 328i exhaust flap - Screwloose

Probably not - but if you're concerned about it, get it repaired.
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Sun 6 Apr 2008 23:47
99 328i exhaust flap - x332race
Thanks I have done so. The vacumn pipe was perished where it attached to the exhaust and had a big hole in it.

Just wanted to find out what it did....

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Sun 6 Apr 2008 23:51
99 328i exhaust flap - Screwloose

I haven't researched BMW's reasoning for it; but it's likely linked to the dual-path inlet manifold to change the pulse tuning of the inlet and exhaust as a pair.
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Tue 8 Apr 2008 15:29
99 328i exhaust flap - x332race
Here is the official BMW explination:-

Thank you for your email to BMW Customer Information.

We can advise that the exhaust flaps adjust at differing engine speeds in order to make the most effective use of the exhaust silencer. When the vehicle is running at idle or at low RPM, the flap ensures that the exhaust gases use as much of the silencer's volume as possible, keeping exhaust noise down, e.g. when you're in slow traffic or driving in high gear.

Whereas when the vehicle is running at high RPM, the exhaust flow characteristics are adjusted by the flap to give the exhaust gases a more direct route through the silencer, thus using less of its volume. This also has the effect of allowing the engine to rev more freely as there is less restriction on the exhaust flow.

The primary reason for the flap is to make the most effective use of the exhaust silencer volume at differing engine speeds.

We trust this information is of some assistance to you but if we can help you further at any time, please do contact a member of the BMW Customer Information Team.

Yours sincerely

BMW Group UK

Elfriede McNeal

Product Information Advisor

Ellesfield Avenue

Bracknell

RG12 8TA




Tel: 0800 325600

Fax: 0870 5050 206

Email: customer.information@bmw.co.uk

Website: www.bmw.co.uk

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Tue 8 Apr 2008 16:26
99 328i exhaust flap - Screwloose

So it's just for noise; there's nothing new about that - I remember a similar cable-operated gizmo on a pre-war Bentley that diverted the exhaust past the silencer.
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