Sonoma Historic Motorsports Festival
Saturday June 2, 2018
Nothing quite equals the sensation of being pressed back hard into the driver’s seat as you accelerate. Feeling that firm, linear g-force has speed written all over it. For the fortunate few who purchased the 911 Carrera RS 2.7 in 1973, this was the feeling that awaited them. This was the 911 at its absolute best; a car developed for competition and powered by an air-cooled six that was capable of taking on Ferrari’s twelve-cylinder Daytona and De Tomaso’s V8 Ford-engined Panteras in GT competition.
The need for a car like the RS 2.7 was, in many ways, the result of the aforementioned Italian makes, which were threatening to win the GT class by sheer brute power. Despite the car’s more agile handling, the 2.4-liter 911S needed a more competitive edge by the 1970s, and Zuffenhausen’s creation of the Carrera Rennsport 2.7 was that edge honed to perfection.
In 1972, the highest-performance Porsche model, the 911S, was being punished for breaking the laws of physics. The original body, designed by Butzi Porsche, had finally reached aerodynamic limits that the Weissach engineer’s improved powertrains and suspensions were capable of exceeding. With the 911S approaching speeds of 150 mph, race drivers were experiencing lift at the rear, resulting in less than desirable oversteer through fast corners, and challenging even the best factory drivers to keep their cars under control. The RS 2.7 then, was a carefully engineered redress, a lighter, more powerful, better-balanced, and more aerodynamic version of the 911S.
The fundamentals of the RS had already been established in 1967, by Ferry Porsche’s nephew, Ferdinand Piëch, who developed the 911R in the experimental department of the new Weissach engineering and testing facilities. Powered by an engine derived from the Carrera 6, the 911 body was made lighter and fitted with fiberglass front fenders, doors, decklids and bumpers. Piëch’s department had built three prototypes and another 20 were assembled at Zuffenhausen and fitted with steel bodies manufactured for Porsche by the Karl Baur Company of Stuttgart. The cars, equipped with 911S shocks and anti-roll bars, 901/22 engines with Weber 46IDA3C1 triple-throat carburetors, and Nürburgring (competition) gear ratios, were all painted white, and had lightweight interiors with Scheel bucket seats. Though some were sold to privateer racing teams, most were used by the works team. But that was as far as the 911R project went in 1967. A proposal to build 500 for homologation as Grand Touring cars never got past the sales department, which determined that 40 cars a month would have to be sold in order to reach the required sales figures necessary for homologation. Obviously no one at Porsche had ever spoken to Enzo Ferrari about getting around homologation rules!
Five years later, following the appointment of Dr. Ernst Fuhrmann as chairman of the Porsche executive committee in March 1972, the decision was finally made to develop a racing-type 911. As Porsche’s Technical Director in 1971, Fuhrmann had realized the time had come to take advantage of Porsche’s experience in Can-Am racing and translate that to the 911. “At the moment,” said Fuhrmann in 1972, “we are ready to harvest the fruits of those years with the 908 and 917.” The first car to be developed was the 1972 Carrera RS 2.7, essentially a refined version of Piëch’s 911R.
As with the 911R, mass was again the first factor to be addressed. Every part of the 911 was attacked to reduce the homologated weight of the RS. The Carrera body was lightened with the use of thinner than standard sheet steel measuring 0.70mm (the usual was from 1.00 to 1.25mm) for the doors, roof, luggage compartment lid, front fenders, luggage compartment floor, rear seat recess in the floorpan, even the shift lever platform. Weight reduction was also achieved through the use of lighter Belgian-made Glaverbel laminated safety glass all around. Another 7.7 pounds was shaved by equipping the cars with Bilstein shock absorbers, marking the first time that the German-made gas-pressurized shocks would come as standard equipment.
Every conceivable facet of the Carrera’s construction was scrutinized for ways to reduce weight; much of it being achieved in small increments. Most of the interior soundproofing was removed and the regular carpet was replaced with lightweight black needle felt. Interior trim was cut down to only the essentials, and even they were simplified—flat door panels with a leather strap to operate the latches, and a small plastic handle to pull the doors closed. These were ex-Fiat 500 parts! The dashboard was the standard 911 design, but with only essential instruments, no clock. The interior was stripped of every non-essential item. There was not so much as a passenger-side sun visor or glove box door. The rear +2 seats were absent and thinly-padded buckets with adjustable head restraints, rolled edges and lightweight cloth upholstery replaced the Recaro driver and passenger seats used in the 911S. Also missing from the Carrera RS were undercoating, doorsill trim, coat hooks, and springs to counterbalance the front deck lid. The engineers left nothing that wasn’t essential to the operation of the car.
From the outside, the Carrera RS 2.7 was distinctively identified with Porsche’s bold CARRERA script running the length of the sills between the wheel openings, and a Bürzel (German for “duck’s tail”) fiberglass rear deck lid. This was fitted with rubber quick release clamps rather than metal latches, again to cut down on weight. The real advantage, however, was the greatly reduced aerodynamic lift provided by the spoiler, which not only reduced the 911’s oversteer problem but added 2mph to the car’s top end—now a lively 153mph. An incidental benefit was that it also raised the pressure at the grille admitting air to the engine compartment, thus increasing airflow to the engine and lowering oil temperatures.
As with the 1967 911R, fiberglass (polyester) was used for both the front and rear bumpers to reduce weight. Larger rear wheel arches on the Carrera also permitted 7-inch rims to be used in combination with the standard 6-inch fronts. The extended fenders widened the base from which two more inches at each side could be added on under the provisions of the GT regulations. The track was 54.0 inches at the front and 54.9 inches at the rear. Porsche was now able to fit Fuchs 15-inch forged aluminum alloy “S” pattern wheels on the 2.7, with either Pirelli Cinturato CN36 or Dunlop SP D4 tires, sized 185/70×15 for the front with lower profile 215/60x15s at the rear. The anti-roll bars were also much stiffer, increased in diameter from the standard 15mm to 18mm in front and 19mm at the rear. As a result, the RS 2.7 could now corner at the highest lateral g. rate of any production Porsche: 0.912. None of the others could break the 0.9 g. barrier.
Under the fiberglass decklid was Porsche’s improved Carrera six-cylinder engine. Since it was larger than 2.5 liters in size, F.I.A. rules allowed displacement to be increased to the next class size, which was three liters. The Carrera had the same stroke as the 2.4-liter Porsche sixes, 70.4mm, but a larger bore, up from 84mm to 90mm. This was the largest bore ever used on a 911 engine to that time, and gave the RS the same piston size and rod length as the 5.4-liter, 12-cylinder engine used in the 917/10 Can-Am cars. The six’s displacement became half that of the twelve, 2687cc or, in marketing terminology 2.7 liters.
The RS engine, designated as the Type 911/83, was essentially much like the 911S that preceded it. The compression ratio was identical, 8.5:1, and the 2.7 used the same Bosch mechanical injection, valve sizes and timing as the 2.4-liter 911S. Output was 210 brake horsepower at 6300rpm, (an increase of 20 over the S) although the engine could easily be pushed well beyond, with the rev limiter set at 7300rpm, maximum torque was rated at 188 lb/ft at 5100rpm, and all this was achieved on regular octane fuel! Drive was carried through a 915 5-speed transaxle as used in the 911S, but with 4th and 5th ratios raised slightly. Porsche claimed acceleration times of 5.8 seconds to 60mph.
Although not publicly introduced until the Paris Motor Show in October 1972, Porsche had started marketing the Carrera RS 2.7 privately to prospective customers months before, in the hopes of bolstering orders to expedite the car’s homologation in Group 4. Following Fédération Internationale de l’Automobile rules, Porsche had to build 500 examples in order to get F.I.A. sanction. As it turned out, reaction to the Carrera was beyond Porsche’s greatest expectations. They had pre-sold 51 cars before the Paris debut and within a week after the show closed had firm orders for the remaining 449 cars! The year’s supply had been sold out in a matter of weeks. On November 27, 1972, the F.I.A. granted Porsche Homologation number 637 for Appendix J, Group 4. Overwhelmed by stunning sales, Porsche decided to build another 500, and when those were sold out by the following April, the factory turned out a third batch. When production of the Carrera RS 2.7 concluded, a total of 1,583 had been built, including the original Homologation cars, giving Porsche a double fait accompli not only had Zuffenhausen exceeded its sales goal by better than three times, the Carrera RS 2.7 could now be homologated in the Group 3 Grand Touring category as well!
Today, the now legendary Carrera RS 2.7 and its variants are among the most prized models for collectors of Porsche sports-racing cars.
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The RS 2.7 models featured are owned by renowned automotive photographer Michael Furman (white 1973 Lightweight) and noted Porsche collector Kent Rawson (red 1973 Touring model). Our thanks to Mike and Kent for their assistance in the preparation of this article. Portions of this article are excerpted from the author’s book Porsche – The Road From Zuffenhausen, published by Random House.
Text and Photos by Dennis Adler
© Car Collector Magazine, LLC.
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Originally appeared in the October 2005 Issue
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