K&N induction filters
I had a K&N air filter fitted at the last (36,000 mile) service. It has made the acceleration above 2,500 revs. (when the valve lift and timing alter) noticeably better without having any detrimental effect on fuel consumption, provided that one does not then proceed to play "boy racers", e.g. blow off BMW`s by using second gear/full throttle up to 69 mph! Incidentally, the lifetime fuel mileage is 70.0 mpg; that is, English gallons, not U.S.