Replaced my 16 year old K&N drop in and...holy shit....what a difference!! The butt dyno says at least 25 more hp, and the blower whine is WAY louder. Much more responsive and powerful. Even though I cleaned it regularly, it appears they do either wear out, not clean well as they age or what ever. But what a difference! Think I'll be replacing it every five years or so. Still a great air filter and cheaper in the long run.