Originally Posted by andrewwynn

The best was the n63 upgrade. Beat exhaust note! My wife literally called in therapy!

(For clarity we upgraded the 3.0i to a 50i X5)

The second best: n55 in the 35i. That one I can use the bimmerlink app to open the second exhaust pipe and it sounds very nice.

Def look into whatever mod it will take. I'm looking into adding a vent on wife's F10 (535 x-drive) becusse she doesn't have the exhaust flap I do it just must have a quieter muffler and both tips active.

305 HP and gets 25.5 avg mpg! Over 50% better than our 3.0i and 35% better than I usually get with same motor in my X5.

Back to topic; for a manual option, installing a plumbing fitting with a simple ball valve was the easy option. I think the guy used a 1/2" or 3/4" ball valve. I can't remember what he uses as the bung, because cast is hard to weld and stainless isn't a cake walk either