I just ran my first tank through my box, and got 31.2 MPG. I did mostly city driving, alot of stop and go, and my engine is nowhere near broken in. I know for a fact that my calculations are correct, and it just doesn't seem like it should be that good. Trust me, I am not complaining, I just wonder why my box is doing so good on gas when I read that people are getting considerably less before the engine is broken in. Weird.....