Porsche revealed the 918 RSR alongside the 918 Spyder concept at the 2011 Detroit show as a demonstration of how hybrid technology developed for motorsport could translate into extreme performance. The project drew on experience Porsche had accumulated with hybrid systems in endurance racing, including the 997 GT3 R Hybrid, which had demonstrated a flywheel-based kinetic energy recovery system in competition.
Unlike the 918 Spyder road car, which used plug-in hybrid technology with a lithium-ion battery, the 918 RSR stored energy recovered from braking through a flywheel accumulator KERS system. This mechanical kinetic energy recovery unit sat beside the driver in the passenger compartment, replacing the co-pilot position.
The 918 RSR's combustion engine is a further development of the direct injection V8 derived from the RS Spyder Le Mans Prototype race car. In RSR configuration the engine was developed to produce 414 kW (563 PS; 555 hp) at 10,300 rpm, a significant increase over the standard 918 Spyder's V8 output. The high rev ceiling of 10,300 rpm reflected the V8's motorsport heritage from the RS Spyder program rather than road car requirements.
Each of the two electric motors provided an additional 150 kW (200 PS; 200 hp) when the flywheel system deployed its stored energy, giving a combined peak power output of 564 kW (767 PS; 756 hp) during boost phases. The gearbox was a six-speed unit developed from the RS Spyder's transmission.
Visually, the 918 RSR used the same dramatic long-tail silhouette as the 918 Spyder concept, with a large rear wing, wider bodywork suited to a racing application, and an open cockpit layout. The design emphasized the connection between Porsche's road car vision for the 918 and its heritage in prototype racing.
The 918 RSR was presented explicitly as a racing variant of what would become the production 918 Spyder, but the two cars shared little mechanically. The production 918 Spyder used a plug-in hybrid system with a 6.8 kWh lithium-ion battery and a combined system output of 652 kW (887 PS; 875 hp) from its V8 and two electric motors. The flywheel KERS approach of the RSR was not carried forward into the road car, as Porsche chose plug-in battery technology for the production program. The RSR concept did not enter production or competition.
The 918 Spyder itself went on to set a Nürburgring Nordschleife lap record of 6:57 in 2013 using the Weissach Package, becoming the first street-legal production car to break the seven-minute barrier on the 20.6 km course. The 918 RSR, as a show car, was separate from those record achievements.
The 918 RSR demonstrated Porsche's intent to connect flywheel-based racing hybrid technology with its upcoming hypercar program at a time when the road car had not yet been approved for production. Its announcement at Detroit in January 2011 came six months before Porsche's supervisory board officially approved series development of the 918 Spyder in July 2010, and it served as a signal that the 918 family would address both performance driving and motorsport audiences. The KERS flywheel approach the RSR used was distinct from the direction the FIA's emerging Hypercar regulations would later favor, but at the time it represented a credible high-performance alternative to battery hybrid systems.