Here's K&N's claim to horse power: the K&N Filtercharger® was a true design breakthrough in air filtration technology. Today, it still is. Because K&N's Filtercharger® can actually double air flow, which, in turn, adds up to 15 extra horsepower.

Unless you got yourself a free-flowing V8.. You ain't getting any 15 HP increase. :)  Expect 5 HP max from your K&N.  This is a cheap upgrade and I recommended it to anyone.   My filter is the 3rd from the right.  A cone, cold-air intake is in the works for my engine.