 The period between 1966 and 1971 was possibly the most successful era of the World Championship, with S (5 L sports cars ) and P (3 L prototypes) classes, and cars such as the Ferrari 512S, Ferrari 330 P4, Ford GT40, Lola T70, Chaparral, Alfa Romeo 33, and Porsche's 908, 917 and the Ford GT40 battled for supremacy on classic circuits such as Sebring, Nürburgring, Spa-Francorchamps, Monza, Targa Florio, and Le Mans where the Ford's won 4 years in a row, in what is now considered the Golden Age of sports car racing.In 1972 the Group 6 Prototype and Group 5 Sports Car classes were both replaced by a new Group 5 Sports Car class.These cars were limited to 3.0 L engines by the FIA, and manufacturers gradually lost interest.