Originally Posted by cpiguy
My son had this exact thing done on his M3, except the cutout is just before the mufflers. It cost him $500 total including the valves and switch, including labor to install and weld the valves in place. He did the wiring himself. Sound is awesome open. Better than my $7000 aftermarket system on my M3.
That being said, it does not create any horsepower like my system does. My full race exhaust system gives me about 35 HP. We dyno'd our cars with valves open and closed, and there was 2 HP difference on his car.
So your car had 35hp over his car on the same day and same dyno?
2014 ///M5 Individual Frozen Grey, Silverstone Full Merino, Piano Black, Exec Pkg, Drivers assistance plus, LED Pkg, Bang and Olufsen, 20" 343M Forged Alloy Wheels
Countermeasures: Bel StiR+, Laser Interceptor Quad HP, Zaon MRX
Upgrades: Eisenmann Sport with M Performance tips, Dinan anti-roll bars