The rise of the Porsche 911 Carrera RSR Turbo

The year 1974 will be remembered for many different reasons, depending on where you were living in the world at the time and what caught your eye. For instance, Richard Nixon became the first US president forced to resign, following the Watergate Scandal in August that year. George Foreman and Muhammad Ali faced each other for the highly anticipated ‘rumble in the jungle.’ Eric Clapton hit the charts with his I Shot The Sheriff, while Paul McCartney and Wings recorded Band On the Run. It was also the year that pocket calculators started to appear in the shops, so if you can recall where you were when some of these events above occurred, then our feature will have a ring of familiarity to it.

The background to Porsche’s turbo power

As it happened, in ‘73 a select group of engineers were also working hard, deep within the workshops of Porsche Motorsport in Weissach on a new secret weapon, to be introduced to the world in 1974.
The turbocharged Porsche 917/30 had totally dominated the Can-Am series by winning six of the eight rounds (the other two rounds being won by the turbocharged Porsche 917/10s) in 1973. That same year, the Porsche 917/10 had also won the European Interserie. With such a vast amount of turbocharging experience in motorsport across the world, Porsche logically sought to apply this knowledge to the 911.

At the beginning of 1974, there were already some signs from the FIA that they wanted to change the regulations, moving away from the 3-litre prototypes such as the Matras, Ferraris and Alfa Romeos. Norbert Singer explains, “Instead, they wanted to make more open road car regulations which in the end they called Group 5. Some said it was a kind of silhouette regulation, but this was never mentioned at that time because it was tighter than the American silhouette [cars] that they had. So, Porsche said okay, we are very interested in racing a 911, even though the 911 was the only road car that Porsche produced at that time! But this gave us some support in marketing to have the 911 running more competitively on the racetracks.”

While engine sizes in the Can-Am series had been unlimited in an effort to attract both manufacturers and spectators, a turbocharged 911 had to meet the 3-litre engine capacity limitation. The trouble was that the FIA applied a 1.4 times multiplication formula to turbocharged engines in order to level the playing field with non-turbo engined cars.
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Start of Porsche’s turbo era

The 1974 911 Carrera RSR Turbo is undoubtedly the car that kicked off Porsche’s foray into the turbocharging of race cars. Not only did this car spearhead Porsche’s turbo era, but it was also the first turbocharged race car to compete at Le Mans. Many in the paddock must have wondered how long this turbocharged creation would last in the 24-hour race that year, but the history books are today littered with the monumental success that Porsche’s race cars proved to be.

The 911 turbo racing era began to gather speed towards the end of 1973, which represented a momentous time for the company. This ushered in a growth in Porsche’s motorsport programme that would see it become the most successful race car manufacturer in the world. Running in parallel with the development of the turbo race car, the 911 Turbo road car (930 in other parts of the world) shown at the 1973 Paris Motor Show, was made available to the public as from the end of 1974.
Norbert Singer expounds, “We started this Turbo Carrera project in 1974, and the idea was to have the turbo car on the racetrack as well. We had it on the racetrack already with the 917 in the Can-Am series, but the regulation was different here because there was always this turbo factor of 1.4 to consider. If you have a normally aspirated engine, in those days it was 3-litre divided by 1.4, which gave you the 2.1-litre capacity. And so, the idea was that we would make a smaller turbo engine that we could run in preparation for the forthcoming regulation for the 935, so we ran the Turbo Carrera in 1974. Therefore, we made a very special 911 which was extremely light, just 820 kg. The other challenge was that we wanted to run the turbo car at Le Mans, this meant it was actually the first turbo car at Le Mans.”

1974 Carrera RSR Turbo development

Externally, the 1974 Carrera RSR Turbo differed most notably from its predecessor, the 1973 Carrera RSR prototype (with the Mary Stuart collar), in its rear wing treatment and the solid panels which replaced the rear three-quarter windows. There were numerous other ways in which the later car differed externally, such as its increased width and the raised rear roof section, but more of that later.

While the Carrera RSR Turbo was a very special creation, it used many components from existing or earlier race cars and engines. In order to meet the engine capacity requirement of 3-litre, the 911’s engine had to be reduced to 2142 cc due to the 1.4 multiplication factor, bringing it in just under that limit. Sitting in a magnesium crankcase, the crankshaft from a 2-litre 911 was connected to forged aluminium pistons with polished titanium conrods which ran in Nikasil-coated liners. Machined production heads were utilised and the cams fitted were slightly milder than those fitted to the RSR engine, only the exhaust valve guides were finned to improve cooling. The front-mounted oil cooler was taken from the 908, and the standard vertical cooling fan was now horizontally mounted to improve cool air distribution. The Carrera RSR Turbo was fitted with a single KKK turbocharger as used in the 917/10.

On the transmission front, the 5-speed Type 915/50 gearbox was installed, with specification similar to that used in the production car. No differential was fitted as the fully locked axle as used in the 917/10 and 917/30 (this was favoured by Mark Donohue), was chosen. A sintered metal single plate clutch as used in the Group 4 Carrera RSR was fitted.
Measuring 2.0 metres across the rear fenders, the Carrera RSR Turbo was the widest 911 to date. Despite this very aggressive outlook, the Carrera RSR Turbo was based on a ‘standard’ Carrera RSR chassis. Body panels including front and rear fenders, doors, front and rear lids, and the aerodynamic front chin spoiler were all made of light fibre-glass. The doors had lightweight sliding plastic windows.

Norbert Singer lessened the angle of the rear windscreen, effectively raising the height of the rear window in order to smooth the airflow to the rear wing. The purpose was two-fold, firstly it improved the air-flow over the body to the intercooler situated in the rear engine lid. Secondly, the overall shape of the race car was less dramatic as a result, and this satisfied Dr Ernst Fuhrmann who felt the rear wing looked too radical. Although the rear wing was large, its appearance was lessened by creating two vertical uprights that extended rearwards from the rear quarter lights. This was an innovative move by Singer as it assisted the airflow by channelling it straight into the intercooler. The car’s glass was flush-fitting so as to reduce air turbulence. While these modifications were permitted within the rules for the prototype class, in which the Carrera RSR Turbo was to run, they also served as a valuable test bed for the 935 which was to follow in two years’ time.

The fuel tank was removed from its position up front where most people would have expected to find it, in an effort to balance out the rear weight bias of the 911. However, Singer wanted to move the tank to a position behind and alongside the driver, where its ever-reducing weight would not adversely affect front adhesion. This gave the car a significant 70/30 rear weight bias, but Singer preferred this as it ensured greater and more consistent traction over the rear wheels. These and many other weight-saving measures ensured that the Carrera RSR Turbo became the lightest 911 produced to date.

The suspension and brakes came in for a number changes, based on experience gained from the Carrera RSR and the 917. The suspension was notable in its departure from that found on the roadgoing 911, and incorporated progressive-rate titanium coil springs over Bilstein shocks all round. Adjustable anti-roll bars were fitted front and rear. This suspension setup saved around 30 kg in weight. The steering and brakes came straight out of the Carrera RSR, the brake discs being drilled and having finned callipers. The 10 ½ inch wheels up front came from the RSR as well, and initially the rears were 15 inches wide, but these were soon increased to 17 inches when it was found that wider wheels were needed to cope with the massive torque of the turbo engine.

The 2142 cc engine developed 500 bhp (367 kW) at 7600 rpm and the Carrera RSR Turbo was able to reach 300 km/h on the Mulsanne Straight at Le Mans. Acceleration to 100 km/h (62 mph) was a phenomenal 3.2 seconds and the 200 km/h (124 mph) mark came up in just 8.8 seconds.

Four Carrera RSR Turbo race cars were produced in 1974 and all four were liveried in Martini colours. The only car retained by the factory is this one featured here, chassis #911 460 9101, the other three having been sold into private hands.

Racing history for chassis #911 460 9101

This actual car gracing our feature may not have been the one that finished second in the 1974 Le Mans 24 Hours, but it certainly has its own record of achievements earned the hard way, on the international motorsport stage.
The Le Mans 24 Hours test weekend on 23-24 March 1974 was the first time that the Porsche Carrera RSR Turbo was exposed to its competition. The test session offered a good opportunity for factory drivers Manfred Schurti and Helmuth Koinigg to test the car in a competitive environment. The car, wearing the #10 for the test, recorded the sixth fastest lap time, but in the 4-hour race it posted a DNF as a result of a broken rocker arm.
The first competitive race for #911 460 9101 was the Monza 1000 Kilometres on 25 April 1974. Here, Gijs van Lennep and Herbert Müller converted their twelfth place on the grid into a fifth-place finish overall. This was against the trio of Alfa Romeo 33s that finished 1-2-3, with the Gulf Ford of Bell/Hailwood in fourth place.
The following race was the Spa 1000 Kilometres on 5 May. With the #14 on the door, Gijs van Lennep and Herbert Müller started from sixth place on the grid and finished in a commendable third place, giving the Carrera RSR Turbo (chassis #911 460 9101) its first podium. Although this was an encouraging sign, the Porsche did finish a sizeable five laps adrift of the first- and second-placed cars.

The Nürburgring 1000 Kilometres was a fortnight later, but rather than its normal 1000 km length, the race was shortened to 750 km. Despite this, there was a strong presence in the prototype class with three Alfa Romeo 33TTs and a pair of Matras, as well as a pair of Gulf Fords. Two Porsche Carrera RSR Turbos were on the starting grid making a strong field at the top, what with the Le Mans race just around the corner. Once again Gijs van Lennep and Herbert Müller did the driving, and starting from twelfth place on the grid, chassis #911 460 9101 crossed the finishing line in sixth place.

Unfortunately, in the Le Mans 24 Hour race on 15-16 June, the #21 Porsche of Manfred Schurti and Helmuth Koinigg was only able to complete 87 laps before being retired due to a broken conrod. Having qualified in eleventh place for the start, and while lying in fourth place, the engine succumbed to the pressures of racing. Its sister car, the #22 Carrera RSR Turbo of Gijs van Lennep and Herbert Müller, famously finished in second place overall despite having lost fifth gear after around 18 hours.

The final race for chassis #911 460 9101 was the Österreichring 1000 Km race on 30 June. The race would end in disappointment though, when the car was disqualified for receiving assistance in the pits. Thus, ended a career for a race car that was full of promise and hope, as it was driven into the Porsche Museum on 17 January 1975.

Note

Unfortunately, the FIA didn’t publish the regulation until the end of 1974, and so they postponed the introduction of the Group 5 regulations until 1976. For Porsche, having run the Carrera RSR Turbo for a full season in 1974, it didn’t make sense to run with the car for another year in 1975 as they had already done a complete season. They had built on their already considerable experience with the turbo cars on the 911 and seen how they could improve it, and so they chose to sit out the 1975 season Singer confirmed. This gave the motorsport department enough time to develop the 935 for the 1976 season.

Bibliography

Title	Author(s)	Publisher	Year
Time and Two Seats	János Wimpffen	Motorsport Research Group	1999
The Porsche Book	Jürgen Barth & Gustav Büsing	David Bull Publishing	2009
Excellence was Expected	Karl Ludvigsen	Bentley Publishers	2019
Porsche 930 to 935, The Turbo Porsches	John Starkey	Veloce Publishing	2018

Links to books listed above in our Bibliography will take to you to our review of those books…
Written by: Glen Smale
Images by: Virtual Motorpix/Glen Smale and Porsche Werkfoto