K&N STOCK REPLACEMENT AIR FILTERS K&Ns replacement air filters are designed to increase horsepower and acceleration while providing excellent filtration. We make over 1,200 different replacement air filters for virtually every vehicle on the road. These filters are washable and reusable and are custom designed to fit into your existing factory air box. Their drop-in design means adding performance is simple. With most vehicles you simply remove the disposable air filter and replace it with a K&N. See applicable instruction sheet for details. Our stock replacement air filters for street vehicles are covered by our famous K&N Million-Mile Limited WarrantyTM and will be the last air filter your vehicle will ever need.