While there may be no such thing as “free” horsepower, the K&N Drop-in Replacement Air Filter comes close. Ordinary paper air cleaners do a good job of filtering air, but clog easily, reducing air flow (CFM). A K&N Drop-in Replacement Air Filter used for 40,000 miles will actually out flow a new foam or paper filter. When new, a K&N Replacement Drop-in Air Filter flows double the amount of a foam or paper filter. K&N uses a washable cotton gauze element which is designed for the life of your engine, and will need to be cleaned every 50,000 miles. K&N engineers their filters to fit each application.