Homologation
To qualify for approval, a minimum of 2500 cars of the competing model had to be built in one year, out of 25,000 for the entire range of the model (e.g.: 2500 Subaru Impreza WRX, out of 25,000 Subaru Impreza). Up to 1991, the requirement was a minimum of 5000 cars in one year, without regards to the entire range, but the FIA allowed "Evolution" models to be homologated with a minimum of 500 cars (e.g.: BMW M3 Sport Evo, Mercedes-Benz W201 Evo). Rules also required some of the interior panels to be retained, e.g. interior door panels and dashboard.
However, not all manufacturers who built 500 such models sold them all, some stripped the majority of them to rebuild them as stock models or used them to allow teams to use modified parts. One such example of this was Volvo with the 240 Turbo in 1985. After they had produced 500 such models, Volvo stripped 477 cars of their competition equipment and sold them as standard 240 turbo roadcars. As a result, after FISA's failed attempt at finding an "Evolution" car in any European countries, Volvo were forced to reveal the names of all 500 "evo" owners to be permitted to compete. The other example was Ford, after selling off their entire RS500 stocks, they read the rulebooks and found themselves that rather than using either the Sierra Cosworths or the RS500s, they could use the body of the basic 3-door Sierra, which Ford was discontinuing, and use their Evolution equipment on them. Nowadays, these cars are treated as any other model in the range.
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