Weird Side Effect of a Car with Active Exhausts

[songzunhuang]

So I was sitting in traffic behind a BMW X1. I was really surprised at the state of the exhaust pipes. The one one the left was very dark, which seems normal. The one on the right looked like it was a fake exhaust as it was completely shiny inside!

Right side appears unused.

Active Exhaust.png (1.57 MiB) Viewed 134 times

As this was a long commute, I stared at this for several minutes wondering what the heck could be going on. Surely they wouldn't install a fake pipe for looks?

It bugged me so much that I did some research and learned that the X1 has an active exhaust. The right side opens up only when increased flow is needed. From the looks of the car I was behind, it looks like it is NEVER needed. What a weird feature.

[Sbeaud]

Looks like an opportunity for some clever comments...

[GRNSHRK]

Interesting indeed

Our X5 has something similar, but both sides do function, eventually

On a cold start, the exhaust only comes out of one side for about half a minute, before the other side opens

One has to wonder what BMW is thinking with these setups, besides making things more complicated than they need to be

[hornhospital]

The E36 M50/52 etc had a pair of pipes on the same side of the bumper coming out of the same muffler. One only opened/flowed exhaust at high RPM, controlled by a vacuum line from the intake. The second pipe was normally closed by engine vacuum. At WOT the vacuum dropped and the valve would open the second pipe. A very popular alteration was the "golf tee fix". You removed the vacuum line at the muffler, plugged it with a golf tee, and both pipes were open all the time.