Rule changes at the end of the 1972 season left the Porsche 917 obsolete for the World Sportscar Championship. Building a completely new car to campaign in the prototype class, which now counted for the World Championship was not a really an option. These prototypes were basically Formula 1 racers with a two seater body and the only serious competitors were existing F1 teams like Ferrari and Matra, and British teams using the Ford Cosworth DFV engine. With no recent F1 experience, it would have been too much of an effort to build a competitive prototype racer for Porsche.
Fortunately for Porsche a new European GT Championship was created, for which Porsche's 911 model was eligible, so Porsches European motorsport activities for 1973 were focussed on the Group 4 GT class. Competition would come from Porsche's perpetual nemesis, Ferrari, in the form of the 365 GTB Daytona 'Competizione'. With a displacement which was almost twice that of the largest Porsche 911 engine at the time, the Daytona was the clear favourite. Work was started on a production 911, that could form the base for a racer quick enough to take on the Ferrari.
Chosen as base for the new car was the Porsche 911 S, that had been successful in events like the Rally Monte Carlo and the Tour de France. Main design focus was to save weight and increase the output of the flat 6 engine. The bore of the 2.4 litre engine was increased by 6 mm to 90 mm and with it the output of the now 2.7 litre engine grew with 20 bhp to 210 bhp. To get the added power on the road, Porsche fitted wider rear than front tires on a roadcar for the first time in its history. A lot of weight was saved by stripping the 911 of all luxuries and the use of fiberglass and thin gauge steel for various bodyparts. One of the most legendary Porsches, the 911 Carrera RS 2.7, was born!
To be homologated for the Group 4 class, at least 500 examples of the model had to be constructed. Production of the RS 2.7 started in 1972 and its stunning performance made it an immediate hit. More than enough cars were constructed, securing the Porsche's entry in the 1973 GT Championship. The rules allowed for some modifications to be made to the racing cars compared to the road cars. Most obvious difference between the Carrera RS 2.7 and its racing counterpart, the Carrera RSR 2.8 was the slight displacement increase.
The engine was bored out even more to 92 mm which resulted in a displacement of 2.8 litres. The compression ratio was raised to 10.5 : 1 and together with the displacement increase it resulted in a stunning leap of power of almost 100 bhp. Even wider rear wheels were fitted and to accomodate them the arches were flared even more, giving the RSR 2.8 a very aggresive stance. Porsche 917 derived vented and cross drilled discs replaced stock brakes to ensure that the fastest 911 to date stopped as quick as it went.
At its racing debut at the 1973 Daytona 24 Hours, the 911 Carrera RSR 2.8 immediately proved to be the car to beat that season. After the 3-litre prototype racers retired Peter Gregg and Hurley Haywood took the overall victory, beating the 7 litre Corvettes and 4.4 litre Ferraris. Further success was had at the Sebring 12 Hours and the Targa Florio of the same year. In the European GT Championship, where the RSR 2.8 was originally designed for, it was almost unbeatable, winning six of the nine rounds and the championship.
Throughout the season, Porsche campaigned a 'prototype' version of the 2.8, which featured further modifications that no longer made it eligible for the Group 4 class. These modifications were fitted to a new series of road cars, the 3 litre Carrera RS 3.0, making the RSR 3.0 eligible to race in 1974. The new car continued the 2.8's dominance in the Group 4 class and so did its replacement, the Turbocharged 934 of 1976.
I think a little error slipped into your description of production numbers of the 1973 Carrera RS. As a matter of fact they started with chasis number 9113600011 (produced in 04/1972) till 9113601590 (produced in 07/1973). This means there have only been 1580 original Carrera Rs's divided in roughly three prodcution batches of 500 each. Of those 17 were homologation specials, 200 were Sports versions with M 471 code, 1308 were touring version with M 472 code, and 55 were racing specials coded M 491. In the hope this information might be of any interest I do sign with my most sincere regards
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911 Carrera RS 2.7
Rule changes at the end of the 1972 season left the Porsche 917 obsolete for the World Sportscar Championship. Building a completely new car to campaign in the prototype class, which now counted for the World Championship was not a really an option. These prototypes were basically Formula 1 racers with a two seater body and the only serious competitors were existing F1 teams like Ferrari and Matra, and British teams using the Ford Cosworth DFV engine. With no recent F1 experience, it would have been too much of an effort to build a competitive prototype racer for Porsche.
