Was stuck in traffic last night behind some lady who was too busy on her cellphone.
Here late model 330Ci had a butterfly valve in one of the twin pipes coming from the single canister muffler. It was interesting. Why would they have this? To increase back pressure under certain conditions?
She was a lame slow driver so it was hard to tell the conditions for it's open/close. But there it was. I think it was closing on off-throttle coasting. But I couldn't be sure.
Anyone know about this?
Curious.

 

It's probably to decrease back pressure, rather than increase it. I've seen it open in cases of more than moderate acceleration, but not at all when creeping in traffic.

 

Arospeed makes something that sounds like what you're talking about.

http://arospeed.com/product_in...d=256

I didn't know BMW put it on their exhausts... I just figured it was another shitty *** Arospeed product. I'm sure BMW put a lot more time to engineer and tune their version then Arospeed though.

 

That's pretty strange then. At idle 0mph it was open, gentle accel it was open, no accel (that I could tell) and turning right it stayed open, coming to the stop it closed (leaving 1 pipe open) then opened back up after a wee bit at rest.
Hmmm, anyway, just an OT thread, no big deal.

 

diessel trucks use stuff like that to, Jake Breaks.

 

Isn't a jake brake on the intake side? It's there to induce compression (it's actually vacuum) braking as a closed throttle would do on a spark fired engine.

 

I had that on my 96 328is. I can't remember when it opened and closed but i know light throttle, low RPM would keep it closed to increase low-end torque. Hard throttle, high RPM it was open for horsepower. Mine kept getting stuck open too.