Hi All, in the exhaust outlet on both sides, One pipe has a vacuum operated butterfly Valve, does anyone know for sure just what this is for?.
Is it purely for noise suppression at low revolutions around town, or for back pressure at low RPM's?.

 

Just found the answer
http://autorepair.about.com/library/faqs/bl104d.htm

 

Check out some of our threads on the subject (BTW, many of the posts are from JDN and other "veterans"):

https://5series.net/forums/topic/2861-exhaust-question
https://5series.net/forums/topic/298...uffler-exhaust
https://5series.net/forums/topic/481...ap-open-closed
https://5series.net/forums/topic/381...f-resonators-r
https://5series.net/forums/topic/392...-muffler-valve

 

Thanks Rudy.