#5204: Engine, IPS Shaft w/o starter For use in all Traxxas TRX 2.5 equipped vehicles. Requires use of an electric bump starter or starter box. Does not accept a pull start or the Traxxas EZ-Start™ system. Not for Maxx trucks or other models without flywheel access. #5206: Engine, Multi-Shaft w/o starter Includes threaded crankshaft inserts for "short" and "standard" applications. Requires use of an electric bump starter or starter box. Does not accept a pull start or the Traxxas EZ-Start™ system. #5207: Engine, IPS Shaft w/ recoil pull starter For use in all Traxxas TRX 2.5 equipped vehicles. Pull starter can be removed to install the Traxxas EZ-Start™ system (sold separately) #5208: Engine, Multi-Shaft Marine w/ recoil pull starter Includes threaded crankshaft inserts for "short" and "standard" applications. Pull starter can be removed to install the Traxxas EZ-Start™ system (sold separately). #5209: Engine, Multi-Shaft w/ recoil starter Includes threaded crankshaft inserts for "short" and "standard" applications. Pull starter can be removed to install the Traxxas EZ-Start™ system (sold separately). #5207R The TRX 2.5R features the Powertune™ machined aluminum cooling head that promotes even heat distribution for stable engine temps and rock-solid tuning consistency. Other mods include a new sleeve for improved engine efficiency and better power.