In 1989, FIA introduced the new 3.5 litre Formula One engine rule to Group C, which not many teams were happy about, because few, if any, such engines were available to privateer teams like Joest. The previous fuel economy based rules were gradually phased out in favour of short races with cars that were virtually two-seater Formula 1 cars; existing Group C cars such as Joest's Porsche 962s were given higher weights and lower fuel allocation to make them less competitive. The team would instead compete in the IMSA GTP category beginning in 1990, winning the 24 Hours of Daytona in 1991 with Wollek, Pescarolo, Frank Jelinski, "Winter" and Hurley Haywood. With their Porsche 962 now being outmoded by the Nissans, Jaguars and Toyotas, the team would not score any more victories. In 1993, the Nissan and TWR Jaguar team had withdrawn, and the AAR Eagle Toyota would continue to dominate the series final year. Joest managed to score the car's last IMSA victory at the Road America 500, due to Toyota's absence.