Game Changer - 1974 Porsche 911 Carrera RSR Turbo 2.1
Turbos that stick out as much as those flares.
45 years ago, Porsche had launched the 917/10, a car built for racing in the Can-Am Challenge Cup, North America’s almost restriction-free racing series made for prototypes. The 917/10 was driven by George Follmer, and so, after this car’s dominance in the 1972 championship, the face of motorsport was inevitably changed during the remaining 70’s and 80’s decades. The change was thanks to the fact that the 917/10 was the Stuttgart’s brand first turbocharged racecar, belting out 850hp from a boxer 12 engine.
After two very successful seasons of forced induction dominance, Porsche had realized that turbocharging was the way to go if they wanted to secure more titles under their belt. And so they did; in 1974 the mechanics at Stuttgart took two 2.8l RSRs and modified them, fitting them with 3.0l naturally aspirated engines. This forced them to race in the prototype class, against bespoke prototypes - such as Matra and Ferrari - for the rest of the 1973 season. For the 1974 season, they wanted to introduce a new, turbocharged engine. Since it had to be built under group 5 regulations, the fact that it was turbocharged meant that the engine displacement couldn’t be bigger than 2.1l. And for the mechanics to be able to downgrade the displacements, they used a bore/stroke ratio of 83mm/66mm of the original 911 two-liter engine, so in reality, what they did was they downsized and engine using the measurements required to expand an engine. Those modifications meant that the new 2.1l engine was able to produce 500bhp @ 7.600rpm and 405lb-ft of torque @ 5.400 rpm.
Not having a rear bumper helped shave some weight off...
Of course, all of this had to be lubricated and kept cool. To achieve this, the car was lubricated with a dry sump system, while cooling was in charge of a big intercooler that added to the ‘natural’ cooling of the engine. ‘Natural’, I say, because the engine was mounted in the classic Porsche location, in the back of the car, and this meant that the turbo was sticking out of the whole body of the car, meaning that it’d be constantly breezed by fresh air. Of course, everything has its pros and cons, and this isn’t by any means the exception. Because of the adopted forced induction, turbo lag at low RPM is always a thing, and this meant that the driver had to moderate their driving style during cornering because otherwise it could have very probably ended up in a spin.
As Pirelli’s slogan reads, “Power is nothing without control”, these amounts of power had to be put down on the road in a way. And so it was put down to the rear wheels via a Type 915 5-speed manual ‘box. Chassis strengthening was also required to handle this and to solve this, a steel monocoque was positioned beneath the fiberglass reinforced panels. Both the steel monocoque and plastic panels helped to keep weight down, but Porsche kept on shedding weight. They achieved further weight reduction by replacing the rear torsion bars for new, lighter aluminum arms and titanium shock absorbers, removing 60 pounds (30kgs) off the total weight of the car. The rest of the suspension was composed of MacPherson struts and titanium shock absorbers, together with lower wishbones up front and the aforementioned modifications made to the rear suspension.
Steering was in charge of a conventional rack-and-pinion system while stopping power was provided by drilled and slotted brakes all around. The interior was also obviously stripped down to the absolute basics, and a multilink aluminum roll cage was added together with the racing gauges. All of this brought the curb weight down to a total of 1,808lbs (820kgs), with that allowing for a .61hp/kg power to weight ratio, and 70% of the weight positioned on the back of the car. The lightweight car and the powerful engine combination was good for a top speed of over 186mph (300kph).
The 2.1l Turbo made its debut at the 1974 1000 kilometers of Monza, where it got an impressive 5th place, although the 2.1l Turbo’s best result was securing a podium, finishing second on the 1974 24 Heures du Mans. As if those results weren’t impressive, the German contender secured a third place on the Spa 1000 of the same year.
All in all, the RSR Turbo helped pave the road for well-known machines like the 935 or the 931, further improving Germany’s mastership at turbocharged speed machines. This legacy lives on, fast forward to 2018, and it’s evident that Porsche’s turbocharged monsters eventually paved the way to modern day turbo cars. What remains of the 70’s turbo dominance by Porsche is on the Porsche Museum, in which one of only 4 RSR Turbos is being exhibited.