As the new rules for the 3 litre prototypes were not favourable to their existing low-weight, low-power Porsche 908, Porsche decided against developing a new high power engine that could keep up with the F1 designs of the competition’s – at least in naturally-aspirated form. In 1976 they would return to sport-prototype racing with the turbocharged Porsche 936 racecars after the engines were tested in Porsche 911 versions.

After their successes with the 917 mainly in Europe, Porsche instead decided to focus on the North American markets and the Can-Am Challenge. For that series, larger and more powerful engines were needed. A 16-cylinder with about 750 hp (560 kW) was tested, but a turbocharged 12-cylinder had initially the same power, with more to come. The 917 chassis also had to be lengthened to accept the longer 16 cylinder engine, and drivers complained that this longer chassis did not handle as well.

The turbocharged 850 hp (630 kW) 917/10 entered by Penske Racing won the 1972 series with George Follmer, after a testing accident sidelined primary driver Mark Donohue. This broke the five-year stranglehold McLaren had on the series. The further evolution of the 917, the 917/30 with revised aerodynamics, a longer wheelbase and an even stronger 5.4 litre engine with up to 1,580 horsepower (1,180 kW) won the 1973 edition winning all races but one with Mark Donohue driving. Most of the opposition was made of private 917/10 as McLaren, unable to compete against the 917 turbos, had already left the series to concentrate on the Indy 500 and F1.

The 917’s domination, the oil crisis, and fiery tragedies like Roger Williamson’s in Zandvoort pushed the SCCA to introduce a 3 miles per US gallon maximum fuel consumption rule for 1974. Due to this change, the Penske 917/30 competed in only one race in 1974, and some customers retrofitted their 917/10 with naturally aspirated engines.

The 917/30 was the most powerful sports car racer ever built and raced. The 5.374 litre 12 cylinder (90.0 x 70.4 mm) twin-turbocharged engine could produce 1,580 bhp (1,180 kW) in qualifying tune, with twin turbochargers run up to full boost, a simply astonishing 39 psi (2.7 bar), though it usually raced with around 1,100 bhp (820 kW) at 7,800 rpm to preserve the engine. Whilst weighing only in at 1800 lb (816 kg), giving it a power to weight of 1967.36 bhp/tonne in qualifying tune and 1369.68 bhp/tonne in race tune. The 917/30 dominated the Can-Am series during the 1973 season. The 917/30 could go from 0-62 mph (100 km/h) in 1.9 seconds, 0-100 mph (160 km/h) in 3.9 seconds, 0-200 mph (320 km/h) in 10.9 seconds, and on to a top speed of 260 mph (420 km/h) +, .These staggering levels of performance, the attendant fuel consumption of the engines, and ever increasing risk, has led to the 917/30 sometimes being cited as the car that killed Can-Am racing.