Whats the flap in the exhaust for??

[THREEFISHORANGE]

Just got a 328 touring. It's got a butterfly type flap in one of the tail pipes, what's it for? Just curious, but if i put an aftermarket exhaust on ,. will it have this flap?
Thanks

[chrisr29]

It closes off one of the tail pipes below certain revs. Believe it was to meet noise regs at tickover etc.

Works off of manifold vacuume. Disconnect it if you want and plug the vacuume hose, though it doesn't seemm to make a huge difference to noise levels.

[Shropshiremike]

chrisr29 said:

It closes off one of the tail pipes below certain revs. Believe it was to meet noise regs at tickover etc.

Works off of manifold vacuume. Disconnect it if you want and plug the vacuume hose, though it doesn't seemm to make a huge difference to noise levels.

That's right - tend to notice when I start mine up it's momentarily loud - esp if backed into a walled-corner - then the flap shuts and it quietens down

[pstruck]

Have the same on my 330Ci. If it is working correctly the valve should be open when the car isn't running. It closes at idle, but opens again somewhere between 2-3k revs. There is a small electric valve gizmo behind the rear light cluster which takes a signal from the ECU, this then opens or shuts to allow (or not) the vacuum from the manifold to reach the exhaust flap and open/close it.

Quite a few people remove the vacuum pipe and stick a golf tee (or similar) in it. Makes a bit more noise, but little other noticeable effect. Some complain that the noise a low speed in town becomes irritating - I though like to hear that silky 'six', so will be removing mine soon.

[gti-ted]

I was led to believe that it was something to do with a cold start choke or something of that ilk.

[Modaholic]

suppose for better low-end torque when the flap close

[noneedtolift]

Modaholic said:

suppose for better low-end torque when the flap close

...plus emissions (heating up catalytic converter)

My 335i has one and i fixed it in the "open" position (1 minute job)- much nicer

[Modaholic]

noneedtolift said:

Modaholic said:

suppose for better low-end torque when the flap close

...plus emissions (heating up catalytic converter)

My 335i has one and i fixed it in the "open" position (1 minute job)- much nicer

Thanks Mate
This is my first time to have this reason but it sounds logical.

[eliot]

anyone got any photo's of them? - are they seperate or part of the exhaust? - Maybe I could adapt a pair as exhaust cutouts.

[A S P]

I looked for the flap on my E36 328 today, couldn't find it. It was a rather lame attempt since it was piss wet through outside, but on my E46 328 it was clearly visible. I always felt that with the E46, 330's were far louder than my 328.

[pstruck]

Sorted mine yesterday. Popped the rubber pipe off , bent it double and zip tied it to seal. I now no longer hear the metallic squeak as it opens and closes, plus I get a lovely deep exhaust note right through the range. Love it (and only took 30 seconds)!

[Kerry540]

It is a flap valve controlled by the DME via a solenoid valve to quieten the exhaust note on idle. It is held closed by a light spring and opened by vacuum.
Waste of time!!

Kerry, xxx