Well it depends on what type of track you are running. Usually the .12 engines will turn more rpms (=more speed) but they don't have the torque of the bigger engines. Are you running a tuned pipe and header? Better air filter (than stock)? The 2 speed is pretty much wasted if you are not running on very long tracks where you need the 2nd gear. If you want to compare engines here is the site for it ->http://www.nitroreview.com/compare/homeengines.cfm Click the engines you want, then click compare at the bottom of the page. Also read your other thread, all this is wasted if you car handles like poo poo!!!