In the first season of Grand Am competition there were five classes but by 2004 the series had reduced the number to three categories:

• Daytona Prototype (DP): This class was introduced in 2003 and was established to replace the two existing Sports Racing Prototype groups. To control costs, the cars used a tube frame chassis rather than the expensive composites used to construct most prototype race cars. Also, expenses were contained by limiting modifications and implementing rules that would be in place for five years. Approved to produce the first generation of Daytona Prototypes - for a cost of approximately $400,000 were: Riley Technologies, Doran Designs, Crawford Race Cars, Fabcar Engineering, Chase Competition Engineering, Picchio and Multimatic. Costs were also controlled by restricting the engines to production based motors supplied by Pontiac, Lexus, BMW, Porsche, Ford and Infiniti. Engine displacement was used to determine the weight of a car and whether a five or six-speed transmission could be utilized.
• Grand Touring (GT): In 2004, rules were established that allowed GT and GTS cars to compete in the same category. As a result, 28 different models from 19 manufacturers were eligible for this class. Examples include Porsche, BMW, Chevrolet, Mazda, Ferrari and Pontiac. As with the Daytona Prototypes, engine displacement was used to establish the weight of different makes and models.
• Super Grand Sports (SGS): Cars competing in 2003s Grand Am Cup Series Grand Sport I category were moved to the Grand Am division. Included in this class are production-based cars such as the Porsche 911 GT3, Chevrolet Corvette and Ferrari 360.

As in the past, the season opened in February with the Rolex 24 at Daytona International Speedway and ended at California Speedway. In between these two venues, there were events at Homestead-Miami, Mont-Tremblant, Watkins Glen, Barber Motorsports Park, Mid-Ohio Sports Car Course, Phoenix International Raceway and Virginia International Raceway. There was a total of twelve events with the series competing at Daytona, Watkins Glen and Homestead-Miami twice.

The 42nd Rolex 24 at Daytona took place on the weekend of January 31 and February 1. There was a total of 53-starters (17-Daytona Prototypes, 14-Super Grand Sports and 22-Grand Touring) which was up from previous year. Drivers would compete for 24-hours on the 12-turn, 3.56-mile track which utilized an infield road course and almost the entire tri-oval.

Weather impacted this year’s event. Heavy rain created treacherous conditions, resulting in a three-hour caution period. The situation grew worse and the race was red flagged – the first time since 1989 when the race was stopped for four hours as the result of heavy fog. With the rain subsiding late Sunday morning, the race was restarted at 10:30 am.