sentences:  Engine capacity was limited to 3 litres for the lightest, most advanced Group 6 sports prototype class, while a new 5 litre Group 4 Sports Car class  was introduced for vehicles of which at least 50 examples had been built.Ford's American headquarters organisation withdrew from sports car racing at the end of 1967, leaving those teams committed to running the aging GT40 without factory support.While some teams, such as JWA, decided to go down the Group 4 Sports Car route and began work on updating the GT40, Alan Mann Racing decided to build a brand new prototype car around Ford's recently introduced 3.0L DFV V8 Formula One engine.