Looks like a gate or flapper in the tipepipe?

[tridski]

Looking in the talepipes, the right side looks like it has a gate or a flapper door. Does anyone know what this is. Thanks Dave 2005 325xi

 

[William330]

That's to control the 'noise' coming out of the tail pipe.

I believe it's controlled by throttle, so when you floor it, the
flap opens up all the way.

Someone who knows the specifics, please chime in...

 

[Kirby]

Yes, it's pretty much as William330 has described. It opens at higher engine RPM, and/or car speed, depending on who you ask. It is just to reduce noise at idle, and opens at speed to let the engine breath better. From what I understand, it is spring loaded. Engine vacuum pulls it closed, a spring holds pulls it open.

 

[Wallaby]

You can, what they call, "tee it open" using about anything - I know golf tees work well (hence the name). By teeing it open, you can achieve a throat-ier sound to the exhaust at a much lower rpm & speed.

If you are into to it - try it