The 1991 edition took place across five classes: GTP, LM, GTP Lights, GTO, and GTU. The LM class — for Le Mans-specification prototype machinery — operated alongside the established GTP field, providing additional variety at the front of the pack. Competition from Porsche and Nissan dominated the upper reaches of the entry list, with Joest Racing fielding the privateer Porsche 962 that would ultimately take overall honours.
The overall win and GTP class victory went to the No. 7 Joest Racing Porsche 962, shared by Frank Jelinski, Henri Pescarolo, Hurley Haywood, Bob Wollek, and "John Winter" — the pseudonym used by German amateur racer Franz Konrad. The five-driver combination was a consequence of IMSA's allowance for large driver rosters in 24-hour events, enabling teams to manage fatigue across a full day and night of racing. Henri Pescarolo brought extensive Le Mans heritage to the effort, while Hurley Haywood and Bob Wollek were among the most experienced endurance drivers in American competition.
The LM class was won by the No. 83 Nissan Performance Technology Nissan R90CK, driven by Bob Earl, Derek Daly, Chip Robinson, and Geoff Brabham. Nissan's factory-backed effort had been building momentum through the late 1980s and the R90CK's Le Mans-specification machinery made a strong showing in the dedicated LM class.
The GTP Lights class was won by the No. 48 Acura Spice SE90P, driven by Parker Johnstone, Steve Cameron, Doug Peterson, and Bob Lesnett. Parker Johnstone had become one of the more consistent frontrunners in the Lights category and the Acura-badged entry reflected Honda's growing involvement in American motorsport.
In the GTO class, the No. 15 Whistler Mustang Ford Mustang prevailed, driven by Mark Martin, Wally Dallenbach Jr., and Robby Gordon. The presence of NASCAR regulars Mark Martin and Wally Dallenbach Jr. in the winning GTO entry illustrated the crossover appeal that IMSA GTO held for drivers with oval racing backgrounds.
The GTU class was won by the No. 82 Greer Racing Mazda RX-7, driven by Dick Greer, Al Bacon, Mike Mees, and Peter Uria. The RX-7 again demonstrated its reliability and pace in the smallest prototype and GT category.
The 1991 race is notable for the size of the overall-winning driver lineup — five co-drivers sharing a single car across 24 hours — which was a feature of the era's regulations and reflected the physical demands of endurance competition at Daytona's combined oval-road layout. The Joest Racing Porsche 962 entry, running in privateer colours, demonstrated that the 962 platform remained competitive even as factory programmes developed newer machinery. The race also highlighted the multi-class depth that defined IMSA GT competition at this point in its history, with competitive battles unfolding simultaneously from the outright leaders to the closely-fought GTU ranks.