i have a k&n panel filter in my oem airbox. There is a large cone inside the airbox which i have removed. my car sounds fantastic and revs a bit more freely than before. I haven't used a BMC before but i did have a K57i on my Gti which didn't do anything positive to my car,IMO. if anything I think it caused me more problems than anything and didn't sound any better than a free flowing mini cooper! There, thats my 2pence worth!