Fitted the ACS rear box and tail pipes on my E70 4.8i ( BMW approved ) -with a K&N air filter would recommend this mod as you now have the V8 sound and engine howl when you floor it what a difference being in the car from the sound for the petrolheads (maybe 4 or 5 HP gain as well ) and at low revs hardley louder than the standard system - man now I have a V8 only wish I could afford the X5M .Cheers