Prior to 1966, Group 4 applied to Sports Cars complying with FIA Appendix C regulations, as well as Series Touring, Improved Touring, and Grand Touring cars modified beyond their original Group 1, 2, or 3 homologation rules.
In 1966, the FIA overhauled its categories, redefining Group 4 Sports Cars with a minimum production requirement of 50 units within 12 consecutive months. These vehicles were required to be equipped for use on public roads. In 1968, the FIA introduced a 5000cc engine capacity limit, and for the 1969 season, the production requirement was lowered to 25 units.
By 1969, the FIA International Sporting Code Appendix J established a hierarchy based on 12-month production numbers:
Group 1: Series-production touring cars (5,000)
Group 2: Touring cars (1,000)
Group 3: Grand touring cars (500)
Group 4: Sports cars (25)
In 1970, the limited production sports car category (25 units) was renamed Group 5. Consequently, the Group 4 designation was reassigned to a new "Special Grand Touring" class requiring 500 units in 12 months. By 1971, the requirement for Group 3 series-production GT cars rose to 1,000 units, while Group 4 remained at 500. In 1976, the Group 4 requirement was adjusted to 400 units produced over a 24-month period.
During the 1966 and 1967 seasons, Group 4 Sports Cars were primarily utilized by privateers. While factory teams campaigned Group 6 prototypes like the 7.0L Ford GT40 Mk.II and Mk.IV for outright wins, the 4.7L Ford GT40 Mk.I competed for Group 4 class honors. These categories contested separate titles: the International Championship for Sports-Prototypes (Group 6) and the International Championship for Sports Cars (Group 4).
A regulatory shift in 1968 limited prototypes to 3.0L engines while allowing sports cars to run up to 5.0L. This change, combined with the reduction of the production requirement to 25 units in 1969, allowed the simpler Group 4 cars to contend for overall victories against the more sophisticated prototypes. An updated Ford GT40 Mk.I chassis secured outright wins at Le Mans in both 1968 and 1969. To exploit these rules, Porsche produced 25 units of the Porsche 917, and Ferrari developed the Ferrari 512S with financial assistance from Fiat.
Following the 1970 reclassification, the new Group 4 Special Grand Touring category featured production-based machinery. Notable competitors included the Ferrari 365 GTB/4 Daytona, Porsche 911 Carrera RS, and the De Tomaso Pantera. The category remained active until it was replaced by the Group B GT class for 1983.
Group 4 regulations served as the primary framework for the World Rally Championship until the advent of Group B. During the mid-1970s and early 1980s, manufacturers were required to produce 400 identical cars to achieve Group 4 homologation for rallying. Significant models from this era included the Lancia Stratos HF, Ford Escort RS1800, Fiat 131 Abarth, and the Audi Quattro.
Homologation could also be achieved through the "100-off rule" (clause bb of Art 260, Appendix J). This allowed a manufacturer to homologate a variant of a Group 3 car by producing 100 "bolt-on option kits" rather than 100 complete cars. This rule was used to homologate the 16-valve Triumph TR7 using parts from the Group 1 Dolomite Sprint. The FIA deleted this rule after 1975, and components approved under it were banned effective at the end of 1977.
The transition of Group 4 from a low-volume sports car category to a specialized GT and rally class defined the technical landscape of the 1970s. In circuit racing, the 1968–1969 period represented a unique era where production-based sports cars (Group 4) successfully challenged prototypes (Group 6) for major international honors due to engine displacement advantages. In rallying, the 400-unit production requirement established the baseline for the specialized rally specials that dominated the sport until the transition to Group B in the early 1980s.