I have had the K&N air filter in for about two months, and most of my driving is back-roads with a posted limit of 40mph with the occasional 80mph jaunt down the freeway. I have not noticed an increase in mpg, I have noticed an increase for off-the-line rabbit-starts, but it is small enough that it could easily just be placebo effect. However I did notice a relativelty big increase in noise from the intake (I also have had the elbow removed from day one). As someone who tends to prefer quite over loud when it comes to engines, I actually don't mind it and think it is a little cool.