Porsche considered this too heavy as their Porsche 908/03 were lighter, and this advantage would have been lost . On the other hand, their air-cooled two-valve engine was low on power with , and the development of a new engine would have been necessary. Thus, Porsche did not enter world championship sports car races after 1971 and sold the 908s to customers who would have to add weight to them. Matra and Alfa Romeo were willing and able to compete, but only in selected seasons or events. Also, Ford's successful Formula 1 Cosworth-V8 engine was available for independent chassis builders, but vibrations made it unreliable for endurance racing.