I have a 190bhp A4 1.8T. Is it worth changing the air filter element to a make such as K&N. I know power gains are usually minimal, but is it worth the £40 odd quid it will probably cost. I know normal upgrade alternatives can include closed induction kits etc but don't want to bother with any of that as the car is under warranty. Any advice on air filters for this engine would be appreciated.