BMW 3 series exhausts...

[Tumble]

A while ago, Our Zak pointed out that some 3 series cars had a twin tailpipe arrangement, but that one of them seemed to be a blank pipe... so naturally, this thought randomly occurred to me while i was driving in some start stop traffic the other day behind one. That extra pipe is indeed going nowhere... until the loud pedal is floored... and a butterfly thingy swings open.... I watched it several times.. as the throttle was released and the car came to a halt again, it closed back up...

Now, can anyone tell me what that's all about??

[DaBeeeenster]

Maybe to ensure that the pressure in the exhaust does not drop when it is only using 1 pipe?

[Skii]

Maybe to ensure that the pressure in the exhaust does not drop when it is only using 1 pipe?

Thats what I was thinking, in a sort of muddy, less defined and generally vague sort of way..

[Tumble]

yeah, but why does it open the other one when the throttle's on? why not just have one pipe?

[Butuz]

Gives better sound when on full throttle.

Thats the only reason i can think of.

Butuz

[schrickvr6]

Is it just when the throttle is decked or above a certain rpm? As a more restrictive exhaust would build more torque upto a certain revrange... say 4000rpm then flip open for full flow, much like my inlet manifold does but obviously on the other inlet tract not the exhaust.

[Tumble]

I could n't say if it was full throttle or not, but it happened a few seconds after the car started moving...

[weebroonieuk]

it is exactly for keeping torque and driveability at lower revs , quite a few cars have it , pretty sure the golf r32 has this system too