EFFICIENCY DRIVE
When the FIA came up with new regulations dispensing with the old Group 5 and 6 classes, Porsche had to rise to a new challenge – one that involved building a fuel-efficient endurance racer. The result was the mighty 956…
Looking back at the story behind the legendary Porsche 956
Just when Porsche had it all sewn up, along comes a rule change that turns the race programme on its head. Such was the situation in 1982 when the FIA
(Federation Internationale de l’automobile) decided that the old Group 5 and Group 6 championships were due for an overhaul. Fair enough, you might say, as you need rule changes every now and then to keep things fresh. But for Porsche this was a real blow.
For several years, Porsche had dominated international endurance racing, first with the incredibly successful 935 and then with the equally amazing 936. Between them, they crushed the opposition in Groups 5 and 6, and people (rival teams, that is…) began to mutter behind Stuttgart's back. These mutterings led to rumblings, the rumblings to a major overhaul of the regulations in order to keep endurance racing alive. Nobody likes one-horse races – except, of course, the jockey on that winning horse…
In the 1970s, endurance racing had been dominated by Porsche and Ferrari. The battles between Stuttgart and Maranello were legendary, but the tide gradually turned in favour of the German race team, first with the mighty 917 and then with the equally dominant 935.
The 911-derived sports car had shaken the racing world by its foundations. Here was a car that was instantly recognisable as a production model yet wiped the floor with anything the opposition could park next to it on the grid.
In 1978, Renault announced its intentions to build an endurance racer, concentrating all its efforts on winning the Le Mans 24-hour event. Which it did, convincingly. After that, Renault swiftly waved bye-bye to the world of sports car racing and turned all its attention on Formula One. The Group 6 Sports Car World Championship ultimately died on its feet, leaving the way open for Group 5 'silhouette' racers to take centre stage. BMW entered the fray with its Csl-based racers, but didn't really stand a chance against the might of Porsche and its 935.
So successful was the turbocharged rear-engined coupé that Porsche was happy to step aside in 1978, to leave the way clear
for privateers to carry the Stuttgart torch. Great for Porsche but not for thefuture of theracese ries or, if thetruth be known, for spectators, as virtually every race ended up as a battle between privately-run 935s. The governing body's response was to dump the old numerically-titled race classes in favour of three new 'Groups': A, B and – guess what? – C.
The first two required cars to be built in certain minimum quantities to suggest some form of production, effectively filling thevoid left by thede mise of Group 5, whilethethird – the flagship class – was for prototype racers, governed only by limits on dimensions and, controversially, the quantity of fuel that could be consumed throughout a race. This was seen as an effective way to limit the potential power output of an engine without resorting to restrictive rulings on engine capacity, valve sizes or intake systems.
There was another reason behind the rule change, and that was to try to relaunch endurance racing as a trans-atlantic sport. In the USA, IMSA (International Motor Sports Association) had goneits own way, with a rulebook which was somewhat at odds with the FIA equivalent in Europe. IMSA ignored the European rules by placing greater emphasis on engine capacity, type and manufacturer with little regard to technological advancement, although the ACO (Auto Club de l'ouest), organisers of Le Mans, had worked with the American organisation to promotethe GTP class, which was similar to Group 6 but more restrictive. It would be some considerable time before there was any unity.
“JUST WHEN PORSCHE HAD IT ALL SEWN UP, ALONG COMES A RULE CHANGE…”
The decision to restrict overall fuel consumption in Group C was made to allow individual manufacturers to develop their own engines in their own way. It didn't matter if you wanted to build a flat-six or a V10, fuel-injected or twin-turbocharged – what did matter was that you only consumed fuel at a given rate. To this end, there were deemed to be three different ways of policing this.
First was to reduce the capacity of the fuel tank, at the same time limiting the flow rate of the refuelling rigs. That way, if you consumed fuel at too high a rate, you'd lose more time sat in the pits as the tanks were filled.
Second was to place some form of flow restrictor between the fuel tank and the engine – much like the controversial device installed on recent F1 cars. Well guess what? The idea proved to be equally controversial back then, too.
The third suggestion was to impose a maximum fuel consumption figure by one of three ways: either by allocating a given volume of fuel for each specific race, by limiting fuel tank capacity or by restricting the total number of refuelling stops at each event.
Each idea had its merits and faults. The first proposal was rejected on the grounds that teams would likely develop evermore powerful, less fuel-efficient engines which would allow drivers to drive like hell to make up for time lost in longer pit stops. Not exactly the most fuel-efficient racing, then. There was also the concern that the pits would become congested as cars would need to be refuelled more often.
The second idea – that of having a restrictor fitted in the fuel line – would mean that drivers wouldn't have to worry about conserving fuel while they were racing, and that there would be less chance of cars running out of fuel on the dying laps of a race. However, the idea was unanimously vetoed by teams on the grounds that any such device (which would presumably be supplied by the race organisers, or at least built to their exact specifications) could prove unreliable in a race situation where vibration, heat and g-forces could affect its accuracy.
So, because it was the easiest to police, the third alternative – that of limiting fuel stops and restricting fuel tank capacity – won the day. It was simple to enforce and relatively easy for fans to understand.
The only problem now was to determine what was an acceptable fuel consumption figure. Paul Frère, best known in later years as a journalist and racing driver but then acting in his role as Vice President of FIA'S Technical Committee, suggested that the Cosworth DFV engine be used as the benchmark.
Producing around 430bhp in Le Mans spec, the venerable British-built V8 consumed fuel at around 30–35 litres/100km (that's roughly 8 or 9mpg). 'No way!', said the manufacturers, who pushed for a minimum figure of 60 litres/100km – that's just 4.7mpg…
“THERE COULD BE NO MOVABLE AERODYNAMIC DEVICES”
Thanks no doubt to the (for once) united front shown by the race teams, they got their way and the first 'fuel-efficient' endurance race series saw competing cars consuming fuel at a rate that would make an oil sheik smile.
But the requirement to abide by a minimum fuel consumption ruling wasn't the only fly in the ointment. Just about every aspect of the Group C regulations differed from those of the outgoing Group 5 and 6 classes. Let's take a look at what Porsche (and its rivals, of course) had to contend with.
Firstly, as far as the bodywork was concerned, there were strict limitations on what we refer to today as the aero package. There could be no F1-style side-skirts (remember them?), and wheels had to not only be covered for at least a third of their circumference, but across their whole width. There could be no movable aerodynamic devices.
The regulations in respect of the aerodynamics extended as far as the underside of the car, too. There had to be a flat surface, measuring 1000mm x 800mm between the rear of the front wheels and the front of the rear wheels. Oh, and no other part of the bodywork could extend below the level of this flat belly-plate, meaning there could be no 100 per cent dependence on ground-effects tunnels to keep cars firmly glued to the road.
There were also limits on the overall size – no car could be greater than 4.8 metres in length, and 2.0 metres wide, while the total front and rear overhangs could not measure more than 80 per cent of the wheelbase. There was also a minimum weight. This was set at 800kg for the first two seasons (1982–83), increasing to 850kg in 1984 when Imsa-specification cars were allowed to compete.
As for the engine, that was to all intents and purposes 'free' – the only restriction was that it had to be manufactured by a company which had cars homologated in Groups A (production cars) or B (grand touring cars). The former required the manufacturer to build a minimum of 5000 examples in a 12 month period, the latter just 200.
But it was the fuel system that came in for some of the most detailed regulation, as one might expect. The fuel tank – a flexible 'bag' tank for safety reasons – could have a capacity of no more than 99 litres, while fuel lines (which should have an outside diameter of no more than 20mm) were deemed to hold just one litre of fuel, making a total of 100 litres of fuel on board at any one time.
As far as refuelling was concerned, each car could only be filled using a gravity-fed rig with a maximum flow of 50 litres/minute, meaning each refill at a pit stop would take less than two minutes – assuming the car hadn't run out of fuel in the meantime, of course.
The number of refuelling stops per event was limited according to the length or duration of the race. For an 800km race, teams could stop four times, for 100km and six hour races, this rose to five stops, while 12 hour endurance events allowed the cars to make 12 stops, and 24 hour races 25 stops.
When Peter Schutz was appointed CEO of Porsche in 1981, he took an active interest in Porsche's motorsport involvement. The company had an illustrious history in endurance racing, starting with class wins at Le Mans as far back as the early 1950s, reaching a high in 1970 with its first outright win with Attwood and Herrmann in the 917. From there, the torch was carried by the 935, followed by the 936. There was, of course, the 924GTR programme, but at best that would only offer Porsche the chance to gain a class win. Schutz wanted more than that: he wanted overall victory.
With that in mind, he gave his blessing to the development of a new car designed to meet the forthcoming Group C regulations. He also made what was to prove one of the most far-reaching decisions of his tenure, and that was to separate the race and production facilities, moving the former to Weissach, while the latter remained at Zuffenhausen. In charge of the new race department was Peter Falk, who had been with Porsche for over 20 years.
The 956 may have come under Falk's jurisdiction but it was Norbert Singer who masterminded the project. Singer had been with Porsche since 1970, joining at a time when the 917 was king, and relished the opportunity to oversee the design of a new car from scratch.
The task of designing a chassis to fit the new regulations was handed to Horst Reiter, while the bodywork and aerodynamic package was looked after by Singer, along with Eugen Kolb. As for the engine, that was the charge of Valentin Schaeffer, with Klaus Bischoff and Walter Naher appointed race engineers.
The programme officially came into being on 20 July 1981, even though the regulations for Group C had still to be finalised. This left barely 10 months to design, build and test the 956 ahead of the Le Mans test day, followed by the race itself in June 1982.
It was an ambitious project with a desperately tight schedule, but when Ferry Porsche was presented with a 1/5th-scale model, there was no turning back…
The 956 was a complete departure from normal Porsche practice, with Horst Reiter turning his back on the previouslyfavoured tubular chassis construction in favour of an all-new monocoque design – a first for Porsche. This method of construction gave engineers a far greater opportunity to exploit ground-effects, with tunnels channelling air under the car. With a tubular chassis, this was virtually impossible. Another benefit of monocoque design was that the chassis was far stronger, offering considerably improved driver protection in the event of an accident.
The chosen material was aluminium sheet, which was then folded, bonded and riveted together. True, that by 1981, the Formula One industry was already using carbon-fibre as the preferred material with which to construct a chassis, but Reiter was as yet unconvinced of its ability to withstand the stresses and strains of long-distance endurance racing. Porsche did not wish to take any risks that might jeopardise its chances of overall victory at La Sarthe. And of course, aluminium structures
could also be repaired at the track, following an 'off'…
By today's standards, the understanding of aerodynamics in 1981 was at a relatively early stage. Wind-tunnels were in common use, but there were none of the sophisticated computer-controlled moving-road tunnels that are so familiar today. But that did not mean Norbert Singer and Eugen Kolb were unable to work magic with the 956.
The problem Porsche now faced was that the large flat surface beneath the cockpit dictated by the rule book meant that there could be no fulllength ground-effects tunnels under the car.
Instead, the two designers came up with an ingenious solution that allowed air to enter the underside of the car from two areas: 50 per cent under the nose, 50 per cent under the side panels. The air was then channelled into two tunnels at the rear of the car, one each side of the gearbox, leaving only the driveshafts and suspension arms obstructing the flow. To further fine-tune the design, the engine and transmission were tilted up by a few degrees to allow the shape of the tunnels to be optimised.
Powering the otherwise all-new car was a tried and tested engine – the factory designation '935/76' hinted at its origins. This was essentially the same twin-turbocharged unit that had proved so successful in the 936, with its roots dating back five years to the 935. It was economical by race engine standards, consuming fuel at less than 52 litres/100kms (or roughly 5.4mpg), so well within the limits dictated by the FIA'S new Group C regulations.
With water-cooled cylinder heads yet with cylinders still cooled by air, it had proved to be incredibly reliable, and with boost set at a relatively modest 1.1 bar (just under 16psi), the 2649cc six-cylinder engine produced 620bhp. It was used in conjunction with a five-speed transmission.
The 956 was first tested at Weissach in March 1982, where chassis number 956.001, the development car, appeared in rather understated white, grey and beige bodywork. Driven by Jürgen Barth, it showed considerable promise right from the off. More testing took place at Paul Ricard later that same month, this time at the hands of Jacky Ickx and Jochen Mass, followed by another session in May where the two were joined by Derek Bell. Together, the trio put in numerous laps, part of the aim being to get used to the handling with the groundeffects chassis. That the car 'worked' was clear for all to see – it was to prove some 10Km/h faster than the 936.
The first competitive outing was at Silverstone in May 1982, where '001', driven by Jacky Ickx and Derek Bell and sporting its new Rothmans livery, finished second overall, and first in class.
“956S NOTCHED UP FOUR CONSECUTIVE VICTORIES…”
It might have won, too, but nobody had explained to the drivers the full implications of racing with fuel economy in mind. Going all out in qualifying, Ickx put 956.001 firmly on pole but Peter Falk had to explain if they drove like that in the race, they would run out of fuel…
Released for the 1984 season, the 956B was the ultimate development of the 956, designed and built to the 1983 works Rothmans specification, featuring Motronic fuel injection, modified suspension and a one-piece underbody. The Motronic fully electronic and integrated ignition and injection system made much closer control of the combustion process possible, providing more power, better fuel consumption and a more progressive throttle response.
Combined with Norbert Singer's aero development to the underbody, the 956B was the ultimate specification of the 956. Just four 956Bs were originally built for the leading 1984 World Championship privateer teams – one of which is the double Le Mans winning Joest-newman car (956.117) and today just three of these cars still survive, after Stefan Bellof's fatal accident in chassis #956.116.
While the 917 may be the most iconic Porsche Prototype design, the 956/962 Group C cars were by far the most successful Porsche Prototype racing cars built so far. Over the next four years, 956s notched up no fewer than four consecutive victories at Le Mans and proved totally dominant in all avenues of international sports car racing. It proved yet again that if Porsche sets its mind on winning, few others stand a chance. CP