PORSCHE 956 The Porsche 956 was built to win and win it did. With mechanical precision. From 1982 un

One of the most important ingredients for a gripping story is struggle. All the really fascinatinig tales about racing cars deal with the designers' and the drivers' efforts to make the thing go faster (or even merely fast) while keeping it on the ground, making it go around corners without tipping over, slowing it down when approaching those corners, providing it with a passable level of acceleration and top speed, and screwing it together tightly enough so that it can cover the necessary distance without falling apart. On that basis, the Porsche 956 story can hardly be described as an epic; from the moment it first turned a wheel, it was as essentially right as any racing car can ever hope to be. The 956 was a brand new car for a brand new formula, Group C, the replacement for Group 6, and the all-new championship the task of which was to revive the flagging fortunes of sports car racing. Porsche had been faithful to sports car racing since 1949, so it was inconceivable that they would not respond to the challenge of Group C. The most striking feature of the Porsche 956 was its chassis; for the first time, Por-sche built a monocoque for a racing car. There were several reasons for doing this, but the most important was perhaps the least obvious. It was clear that the provision of ground effect aerodynamics, which had never previously been incorporated into a Porsche, would benefit from the use of a monocoque. This method of construction did away with the mass of tubing which is anathema to ground effect, making the incorporation of air-tunnels virtually impos-sible; equally the monocoque can be made substantially stiffer than tube-frame chas-sis, with commensurate improvements in handling and roadholding. Yet another advantage of the monocoque is that pro-duction tolerances are usually less than for spaceframes, and Porsche's monocoques

Silverstone. 1982: debut of the 956 in the hands of lckx and Bell. The car immediately set a new standard for Group C are not twisted, as some of its spaceframes were found to be. Porsche wanted to build a monocoque, because it had not done so before, and the technical aspects of the project appealed. The most fundamental reason did, how-ever, relate to the embryo Group C's then unfinalised rules, which at the time speci-fied a degree of driver-protection which could not have been met with a tubular chassis. In the event, the rules as finally decreed were not as demanding in this respect as the draft regulations had been, so the extra safety inherent in a monocoque turned out to be a bonus rather than a feature made mandatory by the rules. The first example of the chassis was constructed purely for experimental pur-poses, and was not intended to become part of a car. Although it followed the general outline of the definitive chassis, it was simpler in many respects, and lacked many of the detail fittings found on produc-tion chassis.

The material used in the construction of all examples of the 956 was plain sheet aluminium, this being chosen largely because of the time pressures which then existed. Design work com-menced in August 1981, work beginning on the first car in November, with the prototype reaching the test track by March 1982, although it missed the first round of the 1982 World Endurance Championship in April. Although the chassis was satisfactory from the outset, many minor changes were made both to lighten it and to stiffen it, although throughout its career Porsche made no attempt to go for more exotic materials, such as aluminium honeycomb, let alone carbon-fibre. At Weissach it is believed that the privately-made honey-comb chassis, which from late 1984 some teams began to use as replacements for the factory product, are no stiffer than the offi-cial monocoque, and by mid-1988 Porsche still had no definite plans to produce such a chassis itself. One ultra-lightweight sheet aluminium tub was built but it was used for test purposes only, and never found its way into production. Ever since Porsche drew the disastrous shape of the first 917, and had to suffer the indignity of seeing outsiders help transform that shape into one of the most effective sports-racers ever, Porsche has left no aerodynamic matters to chance; the result of intensive work in this field has meant that all Porsches are invariably aerodynami-cally sound by the time they first reach the racetrack. The 956's shape incorporated several features new to Porsche. The ex-treme nose was devoid of the usual intake for oil-cooling air, and was thus very clean, containing only three small ducts, one of which fed the cockpit, the others providing airflow to the brakes. The oil radiators were removed from the customary position in the nose, and were re-sited alongside the rear bulkhead of the monocoque, sharing space with the inter-coolers and cylinder head coolant radia-tors. Grouping all the radiators together not only allowed the nose to be kept sleek, but also helped greatly in the car's balance; they were well within the 956's wheelbase, where they would have minimal effect on the car's behaviour. They could also be fed with air from only two openings, one in the top of each door. Initially, these intakes were formed in the shape of NASA ducts, but early tests at Paul Ricard found the water temperature becoming too high, and showed that the ducts were insufficient for the volume of cooling air required. As a stop gap measure, simple rectangular openings were provided instead, but these proved to be so successful that, although it was in-tended that they be improved eventually, they remained unchanged until the advent of the 1988 season, when the arrival of the Model of the projected shape of the 956 to allow wind tunnel evaluation of its aerodynamics. Porsche used fixed floor rather than superior rolling road testing yet got the overall shape about .

New Motronic 1.7 engine management system required changes to the radiator layout as a whole. Body panels were constructed of Kevlar, fibreglass and aluminium. The undersides of the two optional noses were given aero-foil section, to aid downforce; on their upper surfaces, the two noses had almost identi-cal contours, but the undersurfaces were quite different, so as to provide differing levels of downforce to match the character-istics of the two optional tails. The noses were detachable, a new feature for racing Porsches, and clearly an advantage as they permitted easy removal and replacement of damaged sections. Two types of tail were built and tested before the car raced, both designs being intended for very different purposes. The shorter of the two tails featured high vertical fins and a transverse wing, while on the longer tail the fins were lower, and were also joined by a transverse wing. Overall lengths of all 956s (and their later developments, the 962s) were identi-cal, irrespective of the type of tail fitted; although the tails themselves were of differ-ent lengths, the overhang of the fins was changed accordingly, resulting in no differ-ence in overall dimensions. The purpose of the long tail was to reduce drag, which it did dramatically, as well as to reduce downforce. Obviously the major circuit where this would be an advantage was Le Mans, where the fuel consumption rules of Group C were likely to be a par-ticular problem, due to the high average speeds achievable there. It was also in-tended that the long tail would be used at other circuits, and the rear of the car was engineered so that a switch between the two types of tail, plus swapping of other appropriate components such as shock-absorbers, springs, floor-panel and nose, could be accomplished in around two hours. Wheels were one-piece castings by Speedline.

At the front they were originally 11 inches wide, and 16 inches in diameter, and made specifically for Dunlop Denloc tyres; Porsche had always worked with Dunlop, and there was no question of an-other make of tyre being used. In the early stages it was found that the front rims were too narrow; this manifested itself in a minor understeer problem, but the real difficulty was one of tyre wear, it being relatively unusual for a mid-engine car to suffer heavy wear of the front tyres. This largely arose because the 956's downforce was much greater than that of its predecesor, the 936, but the design had not sufficiently allowed for this. Experiments were carried out using the easily adjustable modular wheels made by BBS, and these resulted in an initial width increase to 12 inches, then a second and final increase to the 13 inches which was still in use in 1988. The wheels were fitted with external plates incorporating internal fan blades, designed to draw air across the brakes and out through the outer face of the wheel. These fans were very effective, but in the early days some temporature-measuring tests produced results which suggested that the fans were only of value when used on the front wheels. This information was then disseminated to customers using the cars, and both works and private entrants abandoned rear-wheel fans. Later, the tests were repeated, and it was discovered that the original results were wrong, proba-bly due to the temperature sensors being damaged; consequently, the revised infor-mation was passed to users, and 956's re-appeared with fans fitted on their rear wheels. The first one-fifth scale wind-tunnel model of the car was sufficient to provide accurate information concerning the balance, drag and downforce of the Le Mans version of the car, so that when the Le Mans configu-ration was subjected to one day's testing at Circuit Paul Ricard, to reset the springs and dampers as appropriate, no other changes were required, and the car's shape was considered correct right from the start. Indeed, the single day's testing at Ricard prompted Derek Bell to say that he pre-ferred the Le Mans version of the car to the short-tail sprint model. Apparently the lower downforce of the Le Mans car made it considerably easier to slide, and so it did not require the precision handling which the sprint car needed. The steering, too, was better on the Le Mans car. Although both versions were actually the same mechani-cally, drivers did complain of rather heavy steering on the short-tail model. This was in part due to the high level of downforce being generated, so the problem righted itself automatically in the Le Mans 956. It was, however, subsequently the subject of some modification, and both castor angle and wheel offset were changed in a suc-cessful bid to lighten the steering effort. The engine of the 956 was a carry-over from the 936/81 which in 1981 had raced, and won, at Le Mans. It was thus one of the few proven parts of the car. Porsche had endured considerable problems (notably with cylinder-head cooling) with the 2.1-litre version of its turbocharged flat-six, as in-stalled in earlier 936s, and so it was decided to produce a new engine for 1981. Basi-cally, this consisted of the block of the 2.1-litre, but with heads derived from those of the 2.8-litre type 935, the whole having much in common with the version intended orignally for Indianapolis, and retaining the Indy maximum capacity of 2.65 litres. Cyl-inders were air-cooled, but the heads were cooled by water; dimensions were very much oversquare, with a bore of 92.3mm and a stroke of 66.0mm. The engine was turbocharged, using a pair of KKK K-26 360 turbochargers, and was rated 620BHP at 8200rpm; power outputs for turbocharged cars have very little relevance, for the out-put can so easily be changed, at the cost of increased fuel consumption, at the turn of an in-car knob. The engine and gearbox assembly was set nose-down in the chas-sis, at an angle of 5 ; this gave additional clearance for the air-tunnels, and, as a side benefit, ensured that the drive shaft angle would never be excessive. Contemporary reports stated that the gearbox installed in the 956 had previously been tested in a 944 at the 1981 Le Mans race, but there appears to be no substance to this story, which Porsche denies. The gearbox was developed specifically for the 956, and since no decision as to the buildi-nig of the 956 had been made until after Le Mans that year, then the gearbox cannot have been tried out beforehand. Between the gearbox, and the engine was a long spacer, housing the clutch.

Originally cast in magnesium, the spacer incor-porated a hatch through which the clutch could be removed, thus permitting clutch changes without the need to dismantle the rear end of the car, a problem which afflicts many mid-engined sports-racers. The clutch housing was later recast in alumin-ium, which increased its weight by some three to four kilos, but it also increased substantially its stiffness, which was the object of the exercise. The large-gauge steel tubing which connected the rear of the chassis to the transmission was also strengthened, both by using heavier mate-rial and additional struts; naturally, this added weight to the car, which in its original form scaled approximately 830kg, some 30kg more than Group C's 1982 minimum weight. Rear end of the original 956. Note tilted drivetrain, bellhousing-cum-spacer, A-frame support for the rear end (to avoid channeling all chassis loads through the engine) and generous provision for underbody diffuser tunnels.

Construction of Porsche's first monocoque chassis. Porsche used a plain sheet aluminium tub whereas rivals sought added rigidity through employment of honeycomb sandwich.

At the front, the suspension was conven-tional double-wishbone, with outboard coil-spring/damper units, the springs being tapered titanium. Rear suspension was unusual, with upper rocker-arms and spring/damper units being inboard so as to keep the space alongside the gearbox clear, and thus allow for more airflow through the ground-effect tunnels. Use of small diameter steel driveshafts helped in this respect. Brakes were ventialed both axially and radially, but at some circuits (notably Le Mans) it is not unknown for the ventilation to be radial only; drilling through the discs can cause cracking, and in cool weather at Le Mans the discs can often run cool enough without such drilling being necessary. Drivers consider the cockpit to be reasonably comfortable, although it was made as small as was permitted by Group C rules. To ventilate the interior, sliding side windows were fitted on early cars, but as a weight-saving measure the sliding panels were later abandoned, and replaced by three or more holes cut, in a vertical row, into the plexiglass. Later ver-sions (962s) racing in the USA were some-

Boost control knob, operating wastegate settings for the twin KKK turbos. Pressure in the twin plenum chambers needed to go no higher than 2.2 bar absolute.

Equipped with ice-boxes, fitted in the wide side sills of the bodywork, and provid-ing iced water to drivers' cool-suits. The same bodywork side boxes housed battery, pneumatic air-jacks, and turbocharger and engine management boxes. Group C was very much a fuel-orientated formula, and at the first event contested by the prototype 956, the car faced severe fuel problems. The Silverstone race in 1982 was run over 6-hours rather than the more usual 1000km, so that the distance the 956 actually covered in that time, 1,118km, turned out to be more than it could cope with happily on the 1000km fuel allowance. There were no problems with fuel allow-ance on the Le Mans cars that year, for a combination of reasons. In the first place, most of the opposition was decimated early on, leaving the 956s to run at a comfortable pace; another major factor was the low downforce bodywork, which cut drag con-siderably. Boost pressure was kept low (only 1.1-bar gauge during the race), and corners were taken in top gear wherever possible. Although the theoretical allow-ance for Le Mans was only 2600 litres, 4.33 times that allowed for 1000km events, the winning 956 managed to cover no less than 4,899km, just 4.38 times the distance cov-ered at Silverstone. The three brand-new 956s which arrived at Le Mans scrutineering were all in long-tail configuration, and had been fitted with digi-tal fuel readouts to allow the drivers to monitor their cars' consumption.

Le Mans cars usually are heavier than their spring-racing equivalents, because of additional equipment carried on board, and the 956s were no exception in this respect. The cars carried tool boxes, which included alter-nator drive belts, these having in the past proved to be most valuable. Although cars ought to be able to cover one lap to reach the pits, whilst using only battery power for ignition, there have been occasions where drive belts have had to be changed in the field. The 956s also carried addi-tional fittings, such as an extra pair of headlights, which are not required in day-light-only sprint races. The three Le Mans 956s, numbered 1, 2 and 3, recorded scrutineering weights of 858, 866 and 868kg respectively. The first Le Mans race produced a dream result; first, second and third, from three starters. The winning car ran almost trouble-free throughout, but it did suffer a puncture, and also required some short stops to adjust the fuel injection mixture settings. Car number two also had a rela-tively reliable run, although it too required attention to the fuel mixture, and also needed clutch adjustments. The third car suffered delays totalling over an hour, after a wheel bearing broke up, and damaged the left rear suspension; the fact that the car could remain stationary for over an hour and still be in third position at the end is an indication of the level of the opposition which faced the 956s. Winning at Le Mans is a tremendous boost for a team, but it can have its draw-backs. The 956, and its descendant, the 962, were extremely successful, but this success resulted in less money being made available than the engineers would have liked (but then, car builders and teams always would like more money). The atti-tude of a winning company can quite often be that if the car can win Le Mans, and every other trophy that's available, then quite clearly it does not need much spending on it. In the case of the 956, there was a lot of truth in that, for a very long time.