Am I back,with a few stupid questions of mine??? At the Essen Motor Show I collected some conversations and product information for sport air filters. Now I’m also interested in installing a sport air filter from K&N 57i Performance Kit or raid hp Max Flow sport air filter kit b.z.w just the raid hp performance kit !! According to the manufacturer you would have a little more power increase 6-10 hp — more torque N/m — should be healthier for the engine — long Le 80000km — but has a different intake noise. Then I drove to my BMW workshop and then they told me if I would let this installation expire the guarantee. Do you have info`s or experience about sports air filters or is this just a game game ?? Mfg. Z4 SHARK