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  Porsche 911 Carrera RSR Turbo 2.1      

  Article Image gallery (70) Chassis (3) Specifications  
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Country of origin:Germany
Produced in:1974
Numbers built:4
Predecessor:Porsche 911 Carrera RSR
Author:Wouter Melissen
Last updated:July 30, 2014
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Click here to download printer friendly versionPorsche had reached the physical limits of the production-based flat-six with the three-litre competition engine developed during the 1973 season. Using the lessons learned with the mighty 917/30 Can-Am car, the German manufacturer turned to forced induction instead. Side-by-side Porsche developed turbo-charged version of the 911 competition and road cars. With the production cars yet to be introduced, the new 911 Turbo racer was forced to compete as a prototype in 1974. As a beneficial side-effect, this also meant Porsche would compete directly with customers running naturally aspirated 911s.

A downside of building a car for the prototype class was that the three-litre displacement limit for naturally aspirated engines had to be complied with. Using the equivalency factor of 1.4 for forced induction engines meant that the new racing could only displace 2,143 cc, whereas the upcoming road car would feature a three-litre turbo engine. To achieve the size reduction from the 2.8 and 3.0 competition engines previously used, Porsche engineers used a bore of 83 mm and the same 66 mm stroke of the original 911's two-litre engine. Underlining the strength of that flat six, introduced a decade earlier, the 911 Carrera RSR Turbo 2.1 featured the exact same forged crankshaft.

Similar in design to the RSR engines used previously, the new turbo competition engine was constructed from lightweight magnesium alloys, and also sported twin-spark ignition. A single KKK turbocharger was hung onto the back of the rear mounted engine. As a result, it was exposed and received some cooling, which was desperately needed to keep the temperature of the turbines under control. The relatively hot, compressed air was fed through an intercooler back to the engine. Depending on the boost levels, the flat-six produced between 470 and 500 bhp at the engine's redline of 8,000 rpm. At lower engine speeds, the dreaded turbo lag was still an issue and required the drivers to adjust their driving style. The potent new turbo engine was mated to an existing RSR 3.0 gearbox, which struggled to cope with the added power.

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  Article Image gallery (70) Chassis (3) Specifications