It is impossible to give an exact value because your results depend on many factors. A true functional ram air hood improves the performance of your ride in the same way a supercharger or turbocharger boosts the air inlet pressure mechanically. Functional Ram Air uses the forward motion of your vehicle to provide the same type of boost. Additionally, youll experience lower air inlet temperatures, unobstructed air flow into your engine air intake at all speeds, and even lower engine compartment temperatures if heat extractors are incorporated into the hood. This high flow rate of cold air into the intake, of course, is what is providing the increased horsepower and reduced fuel consumption. Studies done by the OEM’s in the 70’s showed improvements of 10 to 15 Hp using ram air. We have customers that claim our hood added over 25 Hp. Converting this added power to better gas mileage is up to you and your driving practices. Of course, a simple restyling hood or glue on scoop has ZERO possibility of providing any of these benefits. My own experience with my 2006 Dodge Ram 3500 Diesel was about a 10% increase (~1.7 miles per gallon) with the installation of the hood and interface to my stock airbox.