The Roto Start is currently HPI's hottest hop up option for any Savage 21 monster truck equipped with a 21BB or Force .21-.25 engine. The Roto Start allows Savage owners to replace the stock pull starter with a convenient hand held shaft drive starter system. Conversion is quick and easy. All drivers have to do is replace the engine's pull start unit with a metal gear backplate which acts as an adapter for the shaft drive starter unit. Once installed, starting is as simple as the push of a button. All that's left to provide is a 7.2V rechargeable "stick" battery pack and charger. Complete installation instructions are included.