This may be old news, I caught one of the K&N commercials and it said horsepower gains guaranteed, check the website to see how much.
http://www.knfilters.com/search/prod...x?prod=63-3079
Okay, so it looks like they guarantee a gain, but don't guarantee how much. But, they estimate 31.71 hp increase. I can't tell if that's supposed to be with or without a tune.
I just thought it interesting and decided to share.
I'm not buying one, I went with Rotofab last year. Even if I had known about the K&N it would have been a difficult choice given that it's literally more than twice as expensive as the Rotofab.
I can't tell you what gains I specifically got off of the Rotofab. I didn't do a stock dyno. But dyno after install of it with no tune showed 515, I can't remember which kind of dyno it was. It was at Vengeance Racing in Georgia.
Side note, it's funny, K&N is based out of California and this product is not road legal there.