Contesting the prototype class meant the Carrera Turbo was always going to be up against it in terms its weight and aerodynamics compared to scratch-designed sports racers. However, Porsche’s thinly veiled agenda was preparing for the new Group 5 regulations to be introduced for 1975. Based on the 3-litre RSR, the Carrera Turbo used the same 917-derived brakes with cross-ventilated discs, four piston calipers and titanium hubs. The most radical departure was a new rear spaceframe with coil sprung suspension and titanium springs (in place of the RSR’s torsion bar arrangement). Debuting at 820kg, come the latter half of 1974, Carrera Turbo's were nearing an incredible 750kg. The FIA's prototype rules limited engine capacity to three-litres and didn't allow turbocharged engines to run at more than 1.4 bar. Consequently, for a swept volume of under three-litres, Porsche needed a displacement of 2143cc. This was achieved with a bore and stroke of 83 x 66mm respectively, the Carrera Turbo's Typ 911/76 motor utilising the most exotic components available to ensure it was light, powerful and reliable. There were new pistons and camshafts, titanium con rods from the 906 and a magnesium crankcase (although this was exchanged for an alloy item at Le Mans). A standard forged steel crankshaft was used for maximum durability. Output of the Typ 911/76 motor was a mighty 450bhp at 8000rpm, the compression ratio being dropped to 6.5:1 and Bosch K Jetronic installed.

The wing meanwhile housed five gaping NACA ducts to assist engine cooling and later acquired extra cooling pods towards the end of the season. A flush rear window smoothed air flow to the spoiler whilst at the front, a deep wraparound air dam featured ducts for the oil and intercoolers. Encased in aluminium, the fuel tank was fitted where the rear seats originally would have been, the integral steel rollcage of the 3-litre RSR being exchanged for lightweight aluminium version. During the course of the 1974 season, Porsche constructed four 2.2 Carrera Turbo's, the first two debuting at the official Le Mans Trials. There was also a four hour race that weekend, Gijs van Lennep and Herbie Muller retiring with turbocharger trouble whilst Helmut Koinigg and Manfred Schurti suffered a broken rocker arm. As the season progressed, however, the Carrera Turbo's began notching up some impressive results, especially considering their road car origins. Highlights included second overall at the Le Mans 24 Hours, an outright second at the Watkins Glen 1000kms and a third place finish at the Spa 1000kms, all of which were by van Lennep and Muller. Being a development year, deviations from one race to the next were commonplace, weight, power and aero devices all undergoing continual assessment. The most important development was the arrival of a Typ 911/78 engine with 500bhp, but at the end of the 1974 season, the FIA decided to postpone the new Group 5 Silhouette formula until 1976.