The FR500 name describes racing variants of the Mustang based on the 2005 to 2009 S197 chassis. Ford Racing designed and built "turn-key," competition use cars without VINs (serial numbers were used instead). However, an S197 chassis from 2005 to 2009 model years can be used to build an FR500S or FR500C variant. The FR500S featured a racing version of the 4.6L Ford Modular engine outputting 320 HP (brake / crank) coupled to a Tremec T56R close-ratio 6-speed transmission, while the FR500C featured the 5.0L Cammer R50 engine delivering , via a Tremec T-56R. FR500 race cars vary greatly depending on what racing series they were designed for. Additionally, different sanctioning bodies have required changes to be made to the FR500 original "spec." For example, an FR500C variant was homologated into, the now defunct, Grand Am series
