SMOKESHOWIN1

Hi gang; 2008 BMW 535xi 93,000 miles. I have the double-barrel shotgun exhaust pipes on the driver side. Putting my hand over exhaust when car is running, I notice the (driver side) of the 2 pipes is the one doing all the work, that is, I barely feel it coming out the (passenger side) pipe. Is this normal?

audiophool

Yes, normal. There's a flap in the inner muffler's outlet pipe that is closed at idle. It opens at higher throttle to improve exhaust flow. The flap has two functions when closed: 1, when closed it restricts flow to a quieter muffler. 2, makes the inner muffler become a Helmholtz resonator to tune the sound of the exhaust.

You can find tips online for how to keep the flap open at all times. Or get a JB4 tuner pack and set it up to run the flap open at all times. (That's what I've done). With the flap open at idle, it's only a little louder.

kd7iwp

Yes. There is a vacuum actuated flapper in the right tip that is closed at idle and opens when you apply more throttle. Takes away a lot of the droning noise. Many BMWs do this. You can put your fingers in if the exhaust is not hot and turn the flapper yourself, or hold the actuator arm open to hear the difference.

SMOKESHOWIN1

Thank you for the replies!