Gains are relatively minimal if you are just swapping filters. Supposedly, the K&N's are allowing your engine to breathe better. I dont really know if this is true or not. When I replaced mine, I also cleaned out the airbox and removed the air intake duct covers. There is a little more noise but no REAL noticeable diference in power. One way to check is a before and after dyno run. Kinda pricey to find out you gained 0-5hp.