Maybe a very minor noticable difference in hp. The biggest improvement is in fuel mileage. With the stock air filters I got just under 27 mpg (Interstate driving). With the K&N I'm now getting just under 29 mpg (28.92 to be exact) (Interstate driving). My everyday driving is a mix of 65% interstate and 35% city. I was getting right at 23 mpg, now I'm getting just under 25 mpg.