That's why you use the search feature.
Regardless of what you saw, there is an explanation for it. In this case, I fully imagine that you changed an old OEM air filter for the K&N, and saw up to a 10% increase in fuel economy. Of course, you'd have gotten the same effect just adding another paper filter. It's part of basic maintenance, really.
If you see a guy claiming that he got 3MPG from changing to synthetic oil that's the same weight as his old oil, chances are that he changed from dirty oil to clean oil, and that's where the increase came from.
It's normally all in your head. I mean, seriously - think about it - If it was that easy to bolt on 3 MPG here, 4MPG there, doesn't it seem counterintuitive that some of us here aren't getting better mileage than we are?
Man, I wish I could bolt on about 30 more MPG and maybe an extra 300 HP to my van... and increase it's load carrying capacity to maybe 8,000 LBS, and towing capacity to like 20,000... that would be the limit for my license, basically.
Yeah, that would be nice.
