[creepy coupe]

Anyone with a 335i disconnected the vacum pipe from the N/S silencer box and if yes what’s your conclusion?

[E92Fan]

Yes, I've removed the vacuum pipe. Need to plug it with something - golf tee or a tapped screw, then tie it up out of the way.

Not much difference really - noisier on startup as the exhaust is open all the way, and you get a bit more rasp at low revs. If you don't want the extra noise, keep the vacuum line in.

[doughboy]

Same idea, but I unplugged electrical connection to the vaccum control valve in the boot LHS panel. So no working under the car, or plugging hoses required. No visible warnings either

This stops the ECU being able to operate the exhaust flap and it stays in the default open position.

Initially I thought it only closed when cold as it will open on idle from cold after about 2 minutes. But I get a feeling it closes at very light throttle, even at motorway speeds to reduce droning, accelerate and it opens and you have normal noise levels, but there must be a resonance problem on part throttle that the valve is used to reduce.

At about 80 on a light throttle it is markedly more noisy in the car, try it and see...

[E92Fan]

There is an acoustic resonance at about 1800 to 2200 revs on a part throttle which filters its way into the cabin and starts the rear console vibrating..! Annoying, but nothing that can't be overcome by a few strategically placed strips of adhesive felt!

[doughboy]

I assume their will be model specific resonances, the tourer suffers badly at at about 2.5 - 3.5k with the exhaust flap forced open on a light throttle, flap in service however cures it completely.

[E92Fan]

Originally Posted by doughboy

I assume their will be model specific resonances, the tourer suffers badly at at about 2.5 - 3.5k with the exhaust flap forced open on a light throttle, flap in service however cures it completely.

Yes indeed, I forgot you had the Touring. Makes sense, as you've got an open rear cabin so the resonance will be higher up in frequency.

[creepy coupe]

Originally Posted by E92Fan

Yes, I've removed the vacuum pipe. Need to plug it with something - golf tee or a tapped screw, then tie it up out of the way.

Not much difference really - noisier on startup as the exhaust is open all the way, and you get a bit more rasp at low revs. If you don't want the extra noise, keep the vacuum line in.

I'm finding the extra Tone pleasing

[E92Fan]

Originally Posted by creepy coupe

I'm finding the extra Tone pleasing

I'm glad you find me pleasing

[creepy coupe]

Originally Posted by E92Fan

I'm glad you find me pleasing