I'm curious about this too, can anyone confirm this. TIA.

 

not really, just for noise control. it opens at really low rpm if you floor it (<1500rpm), so it really doesn't do anything for torque.

 

So just to reduce noise at idle RPM.

 

pretty much, but it opens later at part throttle, so you'll hear a bit more of a rumble at 2500 and below if you're driving like a sane human being.

 

is that just your guess?

 

no, mine was squeaky, so I could hear it open in parking decks, etc. it opened the second i hit the gas hard in 2nd and I could hear it close when I lifted off the pedal.

 

no, i meant is your reasoning just a guess? why its there? not when it opens. obviously it will make more sound when opened.

 

it didn't do anything to my low end torque, but I wasn't about to blow the cash on two dyno runs before and after a $15 weld to see if it made any changes...the OP asked if he could do something to increase noise slightly. I answered. I can't see how a flap that opens at 1500rpm at WOT is going to do anything to low-end torque, because if it did affect torque that's a perfect example of when you'd want it closed. if you've got other ideas feel free to post.

the open and close thresholds might be different on the 6 cylinder cars. it may well affect torque on the smaller motors. I don't know because I've not driven a 6 cyl E60 long enough to make that observation. the OP has a 545, or at least it appears so from the topic title, so I can confirm my experience there.

 

the flap or valve was designed by BMW to keep the vehicle quieter at lower pms and louder at higher RPMS

 

+1 for RPI