Porsche has created many iconic racing cars over the years, but none achieved more, or enjoyed a frontline career for as long, as the 956/962 series. In its various forms it was successful between 1982 and 1994, and while Jaguar and Sauber-Mercedes also did a lot of winning, no car better defines the Group C era, or played such a pivotal role.
Veteran Porsche employee Jurgen Barth, son of F1 and sportscr racer Edgar, played a special part in its history. A Le Mans winner himself in 1977 with the 936, he helped to create the rules that produced the 956, and was the first man to drive the finished prototype. And as Porsche's customer boss, he was responsible for ensuring that the 956 became the car of choice for private teams in the FIA world championship and later, in its 962 guise, in the IMSA GTP series.
The Group C rules were created after the old Group 5 'silhouette' and Group 6 prototype categories had ran out of momentum. It was accepted that it was no longer practical to base a successful formula on road cars, due to the endless homologation wrangles that inevitably resulted, not to mention the commitment required from manufacturers.
As Porsche's representative, Barth headed the manufacturer group that was charged with determining a new direction for sportscar racing on behalf of the FIA.
"We already talked about this series in 1979," he recalls, "when the 935 Moby Dick was running. It was about two years in advance, because before you start a new formula you need that time."
The aim was to create a pure racing car with few restrictions. In essence the Group C rules were based on a tight fuel limit and a set of dimensions, giving designers a lot of freedom.
"You just needed to build one car - when we built the 934 we had to have 500 cars, for example. Definitely the choice was prototypes, because we didn't want to keep things like the standard dashboard or standard roof, because you are always handicapped by the aerodynamics.
The Porsche 917 and Ferrari's 512 served as ideals for Group C © LAT
"However, we wanted to keep the standard production crankcase, which was important to convince some other manufacturers. The fuel consumption formula was the most important thing, to develop new techniques and so on. When we said it was a free formula with fuel consumption, there was a lot more interest."
Barth had a pretty good idea of what he wanted to see: "We talked and decided that the 917 and Ferrari 512 were still heroes, so let's go back, and we did.
"When we went into the details of the measurements for Group C, I went into the Porsche museum and measured the windscreen of the 917! We said we wanted the same look of cars, with the same cockpit space."
Porsche boss Peter Schutz was keen on the Group C concept, and knew that the company had to maintain a high profile in motorsport. The board duly gave the green light to the 956 project in early 1981.
"It's funny, when you look at the numbers of wins and the number of cars sold, you find a fantastic line," says Barth. "It showed if we did a lot of races and won a lot of races, we also sold a lot of cars. So we convinced our finance people to do it. Also our chiefs at the time, Peter Schutz and so on, were pro racing. It was advertising for the factory."
The man charged with creating the new car was Porsche veteran Norbert Singer. He wasn't exactly starting from scratch; the latest version of the ageing 936 design was still running, and indeed won Le Mans in June 1981 in the hands of Jacky Ickx and Derek Bell.
However, while that 936 did provide some useful knowledge, the 956 represented a clean sheet of paper. At the same time that McLaren was pioneering the carbon chassis in F1, Singer had to come up with Porsche's first ever aluminium monocoque. It was quite a challenge, as Barth recalls.
"It was done quite fast, except the most difficult thing for us was the change from tube frame chassis to a monocoque, because we'd never done it," he says. "It was quite a new step for Norbert to do it. But I think he studied quite a lot of things, and you don't need to tell a good engineer what is needed and so on.
"It was free for the engineers, and that was the challenge, to build a car that had high performance and low drag for the fuel consumption."
Derek Bell and Jacky Ickx guided their Porsche 936 to victory in the 1981 Le Mans 24 Hours © LAT
From the start the car was designed not just as a works racer, but as a future customer car, so that had to be taken into account when it was designed. The synchromesh gearbox was new, but crucially the company had the perfect engine to hand in the 2.6-litre flat-six twin-turbo. Originally earmarked for the stillborn Indy 500 project, it had been proven in the 935, and had also been used in the 1981 Le Mans-winning 936.
"We took a lot of things out of the store, you might say," adds Barth. "The engine, the gearbox internals, and things like this. A lot of stuff existed already."
The monocoque aside, the biggest challenge Singer and his chassis designer Horst Reitter faced was aerodynamics. The car had to be as slippery as possible, to aid fuel efficiency - but ground-effect-generated downforce was also a priority, and that was still very much a black art as far as sportscars were concerned. It was also essential to get the complex cooling arrangement just right.
In the pursuit of ground-effect the car had the maximum possible floor area, and the engine was angled upwards. Singer used a 20 per cent model until a full size car was ready for testing.
The first prototype was given its shakedown by Barth at the Weissach test track on March 27 1982. He was like a kid with a new toy.
"I always tried to go first time in the car," he remembers. "And after three laps Singer had to wave me in and just check if everything was clean and there were no leaks or whatever. Then I think I drove about 20 laps without stopping. It was fantastic with the ground-effects - it was the first time for me. You try to go a little bit to the limit, and so on.
"The only problem the drivers found with 001 was that Norbert built it on the basis of Jacky Ickx. He's not so tall, and when they built the first seating arrangement out of wood, only Jacky tried it. We were never asked to sit in it.
"The first car was built and it was quite difficult for us because we were always hitting the knees. The next ones he changed the arrangement of the dashboard a little bit, but still it was quite difficult. If you remember later with guys like Hans Stuck, we had to cut the seat to get him down on the floor, otherwise he wouldn't fit in it!"
Ickx and Jochen Mass gave the car its first proper circuit running at Paul Ricard, and were immediately impressed. Meanwhile Porsche's extensive Weissach test programme included driving the car over the bumpy pave course, which left anyone given the task with bruised knees, even with a cushion employed!
The 956 made its competitive debut in the 1982 Silverstone 6 Hours © LAT
The car made its race debut at Silverstone in May. Just a few weeks later the works team showed up at Le Mans with three cars, and the 956 immediately proved competitive in long tail, low drag form.
"It was quite stressful with building up the three cars and things like this... It was a bit tight on the schedule, but otherwise everything went well," says Barth. "We had a test in Paul Ricard before, and I think we did 40 hours, and we knew the car quite well.
"We lost a door from one of the cars, and I had to jump in because Hurley Haywood got sick. I had big problems sitting in the seat, so every time on the straight I had to change position from left to right..."
Ickx and Derek Bell duly led a remarkable 1-2-3 finish for the new car, and that was just the start of the story. Barth built up a new customer department and in 1983 the first cars were delivered. Leading entrants Joest, Brun, Kremer, Lloyd and Fitzpatrick would all find success in the coming years.
For 1984 IMSA's slightly different rules led to the creation of the 962 - essentially a long wheelbase version of the original car. It would not only find huge success in the USA but also by 1987 had become standard equipment in the world sportscar championship.
Over the years Porsche made huge gains on fuel consumption with its Bosch Motronic system, and pursued technologies such as the PDK twin-clutch electronic transmission. A lot of things went back into road cars.
"With the fuel consumption formula we had the possibility of developing new materials, like new oils," adds Barth.
Porsche always faced the tricky dilemma of racing its works Rothmans-backed cars while not alienating its paying customers. Many of the latter developed their own tweaks as they sought to beat the factory cars. Before long teams were even creating their own replica chassis, and fitting Porsche running gear.
"We managed to always keep our customers at the same level as the factory," Barth insists. "In fact, my customer engineers did some developments themselves that we gave afterwards to the factory, so it was to both sides' advantage.
"When customers did their own things they didn't always do things the way they should be done. The best example, though, is Reinhold Joest.. He only did things that the factory did and he was the most successful one. But for me it was no problem, we sold parts, we sold gearboxes, we sold engines."
Brun Motorsport captured the teams' title in 1986 © LAT
Joest won a lot of races, but perhaps the greatest achievement by a customer was Brun Motorsport's victory in the 1986 world championship teams' title, the Swiss outfit beating not just the Rothmans squad but also the new TWR Jaguar team.
Time eventually caught up with the car as Jaguar and then Sauber-Mercedes moved technology along. Joest gave the 962 its final world championship victory at Dijon in 1989, but the car continued to race into 1991. By then it was ballasted to 1000kg - the 956 was originally built for an 800kgs limit - and was making up the numbers behind the Peugeot and Jaguar 3.5-litre 'atmo' engined cars.
Porsche opted not to build a car for the new rules, and old turbo cars weren't able to compete in the 1992 World Championship, reserved solely for the 3.5-litre machines. Without Porsche and its customers, it was unsustainable, and the series collapsed after 1992.
Meanwhile, Stateside as late as '91 the car beat allcomers when Joest won the Daytona 24 Hours. And there was to be one last hurrah at Le Mans in 1994 when the car ran as the 'Dauer 962LM' in GT guise and the Joest team scored a final classic victory to add to the six achieved by the marque in 1982-87.
The list of drivers who raced a 956/962 is extraordinary, and includes F1 world champions Jack Brabham (really!), Mario Andretti, Keke Rosberg, Alan Jones and Ayrton Senna. At the other extreme it was a relatively forgiving car for gentleman racers of modest talent - the sort of people whose presence on the grids has always been essential to sportscar racing.
There was a dark side to the story too, as Stefan Bellof, Manfred Winkelhock and Jo Gartner all lost their lives in a tragic 10-month spell in 1985-'86. Barth points out that in conjunction with the FIA, Porsche subsequently contributed to research into barrier technology, which fed back into improved safety in all forms of motorsport.
The fact that so many cars continue compete in historic motorsport, and are so easy to maintain, is a testament to the work Singer and his colleagues did back in 1981-'82.
As Barth points out, the company always had a knack of making things last: "You always find these things with Porsche cars. Take for example the 908. It was constructed only to do one Targa Florio in 1970, but we won the Nurburgring 1000Km with it in 1980!"
Look out for more Group C nostalgia on the website and in this week's special issue of the magazine.