At the time using their familiar Porsche 962, Brun began work on a new car intended to begin competition in late 1991 and then continuing into 1992, when the new World Sportscar Championship rules would come into effect.

Therefore, instead of buying another chassis, Brun and backer and sponsor Repsol YPF decided to invest in building a new car, naming it the C91.

The design would be similar to most other 3.5 liter Group C cars, using large double rear wings, low bodywork and long high downforce noses.

For the fly-away round in Mexico City, the C91 would show some more potential by lasting 31 laps before a failed starter motor forced it to retire.

The car returned to the series at the Paul Ricard Dix Mille Tours venue, qualifying on pole for and winning both races, being driven by Alex Müller.