Adding the new exhaust and intake will not increase your gas mileage. If it does, it might be by 1 mpg. Hardly worth the cost of the new parts. Between the two you will spend $300 - $700. That is several gallons of gas. I was one of the people that tried the experiment. I'm telling you from first hand knowledge. So don't do it for increased gas mileage. It MAY have given me more low end torque, but hey, I don't have the instruments to measure the tiny bit of power difference :-).