The category's defining characteristic was fuel consumption limits rather than engine displacement restrictions. Cars were required to meet a minimum weight of 800 kilograms and carry a maximum fuel load of 100 litres. Competitors were restricted to five refuelling stops within a 1,000-kilometre race distance, giving an effective allowance of 600 litres per 1,000 kilometres. The FIA designed these rules to prevent the dominant strategy of the late 1970s, in which manufacturers such as Porsche and Lancia had succeeded primarily by raising turbocharger boost pressure to extreme levels in qualifying trim. The 3.2-litre Porsche 935 had been capable of more than 800 horsepower under such conditions. Engines had to originate from a recognized manufacturer with cars homologated in Group A or Group B.
The fuel allowance theoretically made large naturally aspirated engines competitive alongside small turbocharged units, and it encouraged an emphasis on the endurance aspect of competition because all races covered at least 1,000 kilometres.
In 1983 the FIA introduced a Group C Junior class for privateer teams and small manufacturers. These cars had a minimum weight of 700 kilograms and a maximum fuel capacity of 55 litres, with five refuelling stops permitted per 1,000 kilometres — an effective allowance of 330 litres. Although the class had been conceived around two-litre naturally aspirated engines, in practice most competitors used either the 3.5-litre BMW M1 engine or the 3.3-litre Cosworth DFL. Constructors including Alba, Tiga, Spice, and Ecurie Ecosse were among the most active in the class. Group C Junior was formally renamed Group C2 in 1984.
By 1989 the Group C series had achieved a popularity comparable to Formula One. That same year, a WM-Peugeot recorded 405 kilometres per hour on the Mulsanne Straight at Le Mans during the 1988 event, the highest speed ever measured at the circuit. In response, the FIA sought to reform Group C around 3.5-litre Formula One-derived engines in place of the original fuel-economy formula. The new rules effectively benefited only large manufacturers who could afford to develop purpose-built F1-sourced engines, placing the formula out of reach for privateer teams such as Spice and ADA that had sustained the C2 class. The resulting fall in entries led to the 1993 World Sportscar Championship being cancelled before the first race of the season.
The ACO continued to allow Group C cars at the 24 Hours of Le Mans. The 1994 Le Mans was the last event at which Group C machinery was permitted to compete. A modified Group C car entered under Group GT1, the Dauer 962 Le Mans, won the 1994 race after the leading Toyota 94C-V suffered transmission problems. The Porsche 962 derivative was subsequently banned. Several open-top modified Group C cars continued to compete in various championships until they were crashed, retired, or became uncompetitive; the Porsche WSC-95, which used the monocoque of the Jaguar XJR-14 with Porsche 962 mechanicals, won the 24 Hours of Le Mans in both 1996 and 1997.
Beyond the FIA world championship, Group C regulations were adopted across multiple national and regional series. In Germany, the Deutsche Rennsport Meisterschaft allowed Group C entries from 1982 until 1985, when the series was reorganised as the ADAC Supercup, which ran as a Group C-exclusive series until 1989. In Britain, the Thundersports championship initially ran C Junior cars alongside other machinery before a dedicated BRDC C2 Championship was established, running until 1990. The Interserie championship in Europe also ran Group C machinery, and in Japan the All Japan Sports Prototype Championship was created in 1983, with the Fuji Long Distance Series also adopting Group C cars. Both Japanese series ran until 1992. The IMSA GTP class in North America applied broadly similar fuel and prototype rules.
Ford with the C100 and Porsche with the 956 were the first significant constructors in the category. The Porsche 956 was derived from the Group 6 936 tested in 1981. Other manufacturers who joined the series over its lifespan included Lancia, Jaguar, Mercedes, Nissan, Toyota, Mazda, and Aston Martin. Many of these also competed in the IMSA GTP class.
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