PORSCHE 935 (1975)
GERMAN
ONE of the FIA's more momentous decisions during 1975 was to decide that drastic surgery was needed to save long distance racing from an early death. The treatment suggested was to cut the patient in half and separate sports-prototypes from the Group 5 cars which at least have some passing resemblance to road going machines. Group 5 cars last season contested a Championship of endurance rac::es, while the prototypes battled it out over a series of shorter rounds. As there had only been a handful of entries for the 1975 endurance races contested by both prototypes and Group 5 cars the FIA's plan for 1976 did not seem the most rational of solutions to the problems of long distance racing. Surprisingly, and thanks mainly to Porsche, the events turned out to be reasonably successful and the spectators were treated to some interesting and, at times, spectacular racing.
Group 5 cars are built to the 'silhouette' rules which require that they look like production cars, and are to a certain extent, based on production machines. Scope for change is wide and as long as the engine remains in roughly the same position as the production car's there is little to prevent the designer building up a pure racer to compete in Group 5. The appeal of this formula could be gigantic if all the major manufacturers could be persuaded to join in; the sight of Jaguars, Ferraris, Mercedes, Maseratis, de Tomasos as well as BMW and Porsches doing battle at Le Mans, the Tourist Trophy and the other classic races, would pack the crowds in. Unfortunately only Porsche and BMW have made any real commitment to Group 5 racing, and although both of these manufacturers would welcome competition from other companies, it looks as ifthey will have Group 5 racing to themselves for a few years to come. The championship, titled the World Championship of Makes, was to include eleven races in 1976 but, four were cancelled and Porsche won four of the seven left to become Champion manufacturer by a surprisingly narrow points margin from BMW who won the other three races.
The Porsche margin of victory was surprisingly narrow because at the beginning of 1976 the Porsche 935, specially designed for silhouette racing, had looked the surest winner of all time. With two year's development behind it the turbocharged 935 could be expected to waltz away from the normally aspirated BMW saloons, and so it proved in the Championship's first two rounds. Porsche were forced to make a change in the 935's turbocharger's cooling system before the third race and this upset the whole balance of the car. BMW were able to easily win the next three rounds. Porsche came back with two 935s to win the Championship's final two races and clinch the Championship. It is estimated that it cost the Stuttgart company 500,000 marks (that's about £117,000), to solve the problems caused by the switch in cooler position.
Porsche more than any other company have pioneered the development of tu rbocharged cars over the past decade. They became involved in CanAm racing and refused to compete with the massive engine sizes of the cars there. Instead they built a relatively small 12 cylinder engine and turbocharged it. The eight litre Chevrolet V-8 engine couldn't compete and CanAm racing became so dominated by Porsche that it folded up. The same thing happened in Interserie racing in Europe, although that series hasn't folded yet, but it could be renamed Formula Porsche! Using the experience gained from the CanAm Porsche the company built a road going car fitted with a turbocharger, the 911 Turbo. It is from this device that the 935, and the less powerful GT Porsche the 934 is developed.
Built especially for the Martini Porsche team only two 935s were constructed last year, the Kremer Porsche team ran a car which looked like a 935 but this was not the genuine article in that it was converted by the Kremer brothers from a 934 Turbo and lacked the full equipment of the works cars. Just as the 911 Turbo represents one of the ultimates of road going transport so the 935 represents one of the ultimates yet reached by racing car designers. The machine costs arou nd £45,000 not including development costs, and will outperform Grand Prix cars when it comes to top speed and high speed acceleration.
Complying with the spirit, as well as the letter, of the Group 5 rules the Porsche engineers constructed the 935 around the body shell of the 911 Turbo. The shell is stripped and extensively lightened, titanium being extensively used. The original doors, wheel arches, bonnet, bootlid spoilers and wings are thrown away and replaced with fibreglass, while plexiglass windows replace the road car's safety glass. Most manufacturers would be content to reduce the weight oftheir racer to the legal limit not Porsche. The 935's weight is reduced to 170lb below the limit and then ballasted back up. The advantage of this is that the development engineers can put the weight exactly where they want it, 150lb is placed in the front of the car improving front/rear distribution, 20lb is placed on the right of the cockpit to even up side to side distribution which is slightly uneven because the car has left hand drive.
The one major difference in appearance between the production Turbo and the 935 is the front of the car. The Porsche engineers took advantage of a loophole in Group 5 rules to fit a one-piece nose piece which is unbroken by headlamps. These are fitted in the front spoiler rather than above it as on the road car, the aerodynamics of the 935 being far superior to the 911 Turbo's as a result of this change.
Suspension at the front is lifted off the 917 CanAm Porsche and employs wishbones and titanium coil springs. At the rear the production car's semi trailing arms are retained. Bilstein gas filled shock absorbers are fitted to both front and rear, and the rear suspension is adjustable from the cockpit to compensate for the loss in weight as the car's fuel is used up. Massive cross drilled disc brakes, derived from those fitted to the 917, are fitted on all four corners ofthe car. A 2300lb car takes some stopping from 200mph and it is not surprising that the 935's brakes get very hot. Scoops on the nose and in the rear wheel covers take cool air to the discs. Small fins fitted to the wheels and slots in the body also help to dissipate the heat. Even so, at one of the races during the 1976 season the calipers became welded to the discs when the pads of the rear brakes wore away. The Martini 935s started the season with 16 in. wheels on all four corners but Porsche developed special 19 in. five spoke magnesium wheels for the rear, Dunlop made some incredible special tyres for these which were very wide but low, having a height of around two inches.
The Group 5 regulations allow the maximum of freedom in altering the engine, only the basic crankcase and block must be production based. The Carrera's six cylinder engine has its bore reduced from 95mm to 92 in. while the stroke remains at70.4mm, this gives a capacity of 2857cc which when multiplied by the FIA's 1.4 factor for turbocharging works out to 3999.8cc. Other alterations to the standard engine include titanium con rods, Bosche fuel injection, dual sparkplugs and higher turbo boost pressure, these bring the power output of the 935 to 590bhp at 7900rpm. Production car output is 234bhp at 5500rpm.
The problems surrounding the 935's turbocharger cooler came about because the original intercooler, which cools the pressurized air after it leaves the turbocharger, could not be fitted under the engine cover of the production turbo. The Group 5 rules state that body panels should be interchangeable between road and racing car so the intercooler had to be moved. The original cooler, which was in the airflow was an air cooler, because it could not be fitted in the airstream anywhere Porsche had to develop a water cooler to fit to the 935. So it became the first ever Porsche racer to be fitted with water cooling. The change in cooling system upset the whole balance of the car and it was to be three races before the 935 recovered its early season form.
Theworks Porscheteam in both Group 5 and prototype racing was run by Martini Racing last season. Martini has been associated with Porsche for many years and 1976 marked the first season when the team had fully competitive cars and drivers capable of winning every race for which they were entered. The main drivers were Jacky Ickx and Jochen Mass, when both were on GP duty Rolf Stommelen and Formula Super Vee graduate Manfred Schurti took over in the 935's cockpit. The final Championship rounds at Watkins Glen and Dijon saw both 935s entered, in both races the cars finished first and third, these results with the early season runaway victories at Mugello and Vallelunga gave Porsche sufficient points to take the Championship. The Ickx/Mass combination won three races, brake problems accounting for their third place in America. Le Mans was a non Championship race last year and the race was easily won by the Porsche prototype, the 946, driven by Ickx and Gijs Van Lennep, Schurti and Stommelen brought the 935 home in fourth place after a long pit stop following the suspension collapsing. All in all 1976 was a highly successful season for the red white and blue Martini Porsches.
What of the future? It is clear that Group 5 racing could prove to be a highly successful formula with spectacular, powerful cars which are easily indentifiable with production cars. There were however pitifully small crowds at many of the 1976 races, the main problem being that with only Porsche and BMW taking part in the races there are just not enough competitive cars. BMW were developing a turbocharged 300CSI during 1976, and it seems that this will be fully competitive with the Porsche 935 by the opening ofthe 1977 season. This presents another problem, that without a turbocharged car no team will be competitive, the cost of developing such a device is astronomical but unless another company, preferably a non German firm, puts up the cash and builds a turbo car the series will fold up through lack of interest. This is what happened to CanAm racing. Although turbocharging is a technical advance it has limited use to most manufacturers, perhaps there are already sufficient reasons for banning the use ofturbochargers in silhouette racing, or at least reducing the factor employed in calculating capacity of turbocharged engines. Turbochargers do in fact introduce an unreal aspect into racing, as it is possible to increase the blower's boost pressure thereby increasing the engine's power until it blows up. The gap between practice and race times is often wide when turbocharged cars are racing as the boost is increased to get a good practice time. It is not hard to imagine a race situation whereby a team runs one car with increased boost to destroy the opposition before its own engine destroys itself. Clearly only the very richest manufacturers could afford to race if such a situation were to come about.
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