With all filters, your moving the balancing point between performance vs. filtering qualities. If you want to look after your engine, stick with a quality paper filter... if you want balls out performance, go with something like a K&N, but be prepared for more contamination in your engine and oil which will to some degree accelerate wear.

The reason why paper filters get dirty quick is because they actually trap contaminants. They cost £10 a time, so change it twice a year and you'll still be quids in on buying a K&N (or equivalent) and you don't have to faff about cleaning it!

As for better performance? Well, for whatever reason, Alpina decided to use a standard BMW paper filter in my car, which develops over 300bhp as standard, although they did modify the airbox with a huge cold air feed. My advice would be to follow suit, drill a 3" hole in the bottom of your airbox and run a dirty-great pipe from behind your front spoiler

Alpina B3S Airbox:


Rich