Running a BMW with open stacks that see's four seasons of the year and several miles of long dirt roads and driveways in the N. Ga mountains more than 2x a month is absolute suicide. There is a reason Alpha-N cars are typically for the track only. Plus, the resonance the box makes is a way cooler sound than running them open
just make your own stacks with gsxr 1000 tb or any othe bike.its just as good, you can get them fairly cheap,all you need is a intake mani and a welder