 For 1986, the World Endurance Championship became the World Sports-Prototype Championship.Although the Group C formula was a success, with regular crowds of 50,000 to 70,000 at WSC events (a modern Grand Prix in Europe will have similar crowds), and upwards of 350,000 at the 24 hours of Le Mans, the FIA introduced new rules for 1991 at the behest of FIA vice president Bernie Ecclestone; 750 kg machines with contemporary normally aspirated engines, which were purpose-built 3500cc racing units.The new classification, known as Group C Category 1, was designed to mandate Formula One engines.