They call those chips piggy-backs. They actually mess with your car's computer and tell it that the car is getting more air than it actually is sending more fuel to the engine. It just wastes fuel...so if you see something rediculous like "Increse 20 HP and 31% MPG" (You see this on Ebay alot) It's actually .00000020 HP and -31% MPG. We arent driving Dodge Challengers as everyday drivers anymore, so why have the gas mileage like one?? Just be warned, they do little or nothing to increase power, just wastes gas.