i seriously doubt he got 18hp off the k&n filter itself.....seriously doubt
they are nice, you can tell a lil difference, but not a whole lot....i've had one in my last 2 cars(till i went with a CAI with the p5) for mine it was half as thick as an oem paper filter, should(in theory) allow more air through easier.
plus once ya buy all ya need is the recharge kits to clean them, and a kit is like 10 bucks and would last me about a year...i would clean mine every 5k when i would change my own oil....so it would save you money in not having to buy another airfilter ever again, if you change your own oil