any change in gearing would not be any larger than from 5:1 to 6:1 or so. yes you will notice a drop in the rpms of the engine because of the suddenly increased load on the engine. but you need to remember that i am talking about nitro engines that run at insane rpms but mith nearly no torque. gas engines are much more powerful not in horsepower but in torque. are you talking about a 2speed in a large scale gas car or smaller nitro car?