The flapper on other marques is mostly for noise control. But, every boxer is so quiet that I'm thinking it's not for noise control, but for exhaust tuning. I recall when the first GS's came out with twin cams BMW made a big deal about variable exhaust. The ideal back pressure varies with RPM and throttle. Then again, the GS is pretty loud, so maybe the flapper is just noise control.
FWIW, dealer advised me that if I go with aftermarket headers, go with ones that use the flapper. Better mid range they say.
You could try researching on one of the GS boards. They usually know what they're talking about unlike me.
FWIW, dealer advised me that if I go with aftermarket headers, go with ones that use the flapper. Better mid range they say.
You could try researching on one of the GS boards. They usually know what they're talking about unlike me.
