Its a HUGE misconseption that K&N, etc will give you a mileage increase. On any vehicle that has an O2 sensor, the mixture is always being trimmed, so A/F restriction is a non issue. Power can be effected, but the filter has to be quite dirty for that to happen, and only than at WOT. I also don't like the small particles the aftermarket filters let through. There was a good test online, I'll see if I can find it. I have seen alot of hurt Cummins on our trucks from poor aftermarket filters being added, and the engines being "dusted".