Exhaust System

I already have the K&N Gen II CAI, and will soon purchase the shark injector. Just wondering what is the best HP for my buck.

Im guessing the best exhaust for a BMW would be to get a aftermarket exhaust from a BMW tuning company like Hamann, Dinan, AC Schnitzer, Active Autowerke, Alpina, Meistershaft, or Hartge. Maybe even go for brands that only specializes in exhausts like GReddy, Stillen, Flowmaster, Magnaflow, or Borla. If I was you, I’d go with a BMW tuning company from Germany.