e36 328i exhuast with a servo attached?

[whipsey]

what's it there for? it appears to have a vacuum servo attached with a butterfly type thing in one of the two exhaust tips

[leeparkes]

Its for noise, when its ticking over the flap is shut, give it the beans and it opens.

I opened one of these boxes up ill get the pics up

[leeparkes]

[whipsey]

i like it one for the ebay pile then lol just bought a 328 touring to use as my runner but has a bodgy roof repair so have to break it

[mcbunny]

pull the pipe off the servo stick a golf t in it and there you go valve is always open and a nice noise

[George]

As above. Here's a write up I did about it ages ago for the PBMW Forum

Exhaust flap that is! ;)

I have to admit, in some respects the 328i is very decent however in one main area it has been somewhat of a disappointment - aural stimulation.

The 328i simply doesn't sound as good as the 325i. It lacks the bass and 'burble' you get from the standard 325i exhaust, let alone the Supersprint currently attached.

What's the cause of this...well, the flap system in the exhaust has been cited as a contributing factor.



This is dependant on the pressure from the manifold - see illustration above. Item 16 is situated in the boot, the tube runs down and is attached to the 'vacuum box' attached to the tail pipe.

This ensures 'quiteness' at low revs and then as the revs increase, the flap opens and someone turns the volume up.

Nice idea in theory, but imho, I think at any given revs, the sound from the back of the 325i is superior.

Anyway, it is possible to fix this situation by basically removing the tube from the tailpipe box and plugging it up, thus disabling the flap system rendering it permanently open.

So here's how...

1) Locate your exhaust...


Guess which of the pipes has the flap...



And for those who can't see that well...


I tried to get a video of the flap opening and closing with the revs but the steam from the exhaust caused the camera lens to fog up! Unfortunately by pulling the camera back to prevent this, the flap was no longer visible.

Oh well...

2) Look under the car to locate the box/tube

Here you can see the tube attached to the box on the tail pipe


Follow the tube...


And it leads into the boot...


3) Unplug the tube


4) Block the tube


Some people use a golf tee, I used a self tapping screw. The result is the same.

Place the tube cunningly to avoid flapping around and that's it.

Does it make a difference?

Well imo, certainly. At idle the the note is a bit bassier and on the road between 2-3k there's some more meat to the exhaust noise replacing the flatness that was there previously.

Here's some videos, I apologise for the poor quality. There were workmen up the road making a racket and furthermore thae mic on the camera has made the exhaust sound very clattery which I can assure you it is not.

Before:


After:


And that's it.

Not sure how applicable it is to other models? E39 528s for example. I assume BMW use a similar system on their new cars too?