This is a Long Crankshaft Version of the Traxxas Pro TRX-15 Engine. It is for modelers who want higher performance than a .12 size engine in their 1/10 scale kits such as Nitro Hawk, Buggy and Street. This Version Comes With a Pull Starter. COMMENTS: For the Pro 15 with the Short Crankshaft, use TRAG4007. If you have any other kit, I would call that manufacturer or call Traxxas directly at 1-888-TRAXXAS. Traxxas engines run much hotter than normal engines (O.S., ASP, ThunderTigre, etc.). Therefore, Traxxas recommends their Top Fuel (TRAP5010) and their glow plug (TRAG3230) to run the engine cooler.