Cars & Racing | 29 March 2016Porsche Turbo: Solutions Share article facebook twitter google pinterest The Porsche Turbo has been involved in some pretty memorable events in the history of sports cars since its first model came out in 1964. The following excerpt from Randy Leffingwell’s book Porsche Turbo: The Inside Story of Stuttgart’s Turbocharged Road and Race Cars tells the story of one moment of possible doubt during the progression in the manufacturing of the acclaimed Porsche turbo. The intercooler sat outside the body “package,” projecting up into an airstream directed by a massive set of ducts formed into the large rear wing assembly. Porsche Archive LOOKING FOR SOLUTIONS Ernst Fuhrmann already had made signi?cant contributions to the 911. In early 1972, he watched 911 racers at Hockenheim struggling to control their cars on corners. He challenged his staff, and within a short time a young aerodynamics engineer named Tilman Brodbeck developed a front air spoiler that split the air?ow around the front end and signi?cantly reduced front lift. Ferdinand Piëch, in one of his last acts before departing from Porsche, accelerated the testing schedule so that the front spoiler went into production as standard equipment on 1972 911S models. When Piëch left, Fuhrmann appointed another young engineer, Helmuth Bott, to take his place. The new front spoiler exaggerated rear lift, so Bott sent Brodbeck back to the wind tunnel and, together with a stylist, they devised a rear spoiler, now well known as the Bürzel, or ducktail. This debuted in October 1972 on the 911 Carrera 2.7 RS, a car created speci?cally to qualify 911 models for FIA Group 4 production class racing. During the following eighteen months, the 2,687cc engine grew to 2,806cc for a competition version, then again to 2,993cc for a 1974 roadhomologation RS and a competition RSR. These cars achieved great success as engineers meticulously improved every part while studying racing rules in great detail. But other competitors were not standing still. Enzo Ferrari had a powerful 4,390cc Daytona 365 GTB four-cam, 4,390cc V- 12 coupe and Alessandro de Tomaso had installed 5,752cc Ford 351 Cleveland V-8s in his Pantera. The Panteras were exceptionally fast while they lasted, but the Ferraris were both fast and durable. Ernst Fuhrmann’s words echoed in his engineers’ ears: “There must be room.” Yet another iteration of the rear wing appeared. NACA-style ducts in the wing supports directed airto the intercooler. Porsche Archive FINDING ROOM Hans Mezger and Valentin Schäffer labored in the competition shops to turbocharge a ?at six for the World Endurance Championship. Group 5 was of particular interest, a category Ian Bamsey described in A History of the Turbocharged Racing Car as “catering for radically modi?ed production cars, retaining little more than the engine block, engine position, and the silhouette of the base model. . . . The new category was slated for introduction in 1975 so in ’74 Porsche entered an experimental turbocharged derivative of the Carrera RSR GT model in World Championship of Makes races, exploiting the freedom of Group 6 prototype regulations.” The Typ 911/76 engine for 1974 had to ?t within Group 6’s maximum displacement of 3,000cc. In this category Porsche competed against 480-horsepower, ultra-low drag-sport-racing prototype V-12 Spyders from Matra. Ford Cosworth 2,993cc double four-valve (DFV) V-8 engines adapted from Formula One delivered 450 horsepower in sleek Spyders from Mirage, sponsored by Gulf. Pushing the weight and shape of the 911 through the same air as these slinky competitors made turbocharging mandatory to produce enough power to become competitive. However, CSI regulations stated, as Paul Frère reminded readers, that while “supercharged engines of any kind used for any sort of racing, except Formula 1, were considered to have a capacity 1.4 times actual swept volume (in Formula 1 it is twice), it also meant that the engine capacity had to be reduced to no more than 2,142cc in order to fall within the 3-liter capacity limit.” Helmuth Bott’s competition engineers went to work. While they adapted the fundamental steel body structure, they ?tted wafer-thin ?berglass front and rear deck lids, fenders, doors, and front and rear valences in place of stock steel. As Frère pointed out, these cars had “no bumpers in this case, not even token ones!” As the car was a prototype, Weissach’s inventors were allowed to move the 31.7-gallon fuel tank from the front to the passenger compartment, very close to the car’s center of gravity. Rules demanded they mount it inside a welded-steel shield. In this position, as the car consumed fuel supply and weight, this no longer affected handling. Relocating the tank from the front trunk made space available for front brake-cooling air ducts, although this eliminated the spare wheel (required by Group 6 rules), and the fuel lightened the front end. Bott’s engineers bolted an aluminum tube framework into the body rear to support the engine, transmission, and rear suspension. This allowed them to remove the stout cross tube that anchored the suspension and supported the engine on series-production cars. At one point when Fuhrmann was concerned about the car’s weight, he suggested engineer Norbert Singer adopt American NASCAR techniques. Singer explained the concept in an interview in 2005: “The NASCAR teams soaked the car bodies in acid to get rid of metal and weight. Dr. Fuhrmann said we should reduce the thickness of our metal by half everywhere it was practical. He thought this might take maybe [150 pounds] out. He had us at a dinner and said no one would eat until we agreed to a plan for this. So I said okay and we ate.” Singer searched throughout Germany and found a company that said it could do it. “They quoted 50,000 to 80,000 deutsch marks [roughly $19,400 to $31,000 at the time], which was very expensive,” he said. “I asked why. They said they had to build a tank big enough and buy the acid for it! Dr. Fuhrmann was surprised, and when I explained the reason, he was angry. Then he said, ‘No! We don’t do that!’” By the time engineers ?nished with their more sensible modi?cations, some weight shedding, and a radical front and rear suspension recon?guration, they had reduced the 1974 RSR’s weight to 1,819 pounds. This was still heavy, however; Group 6 operated under Group 5 weight limits, and the minimum permitted was a startling 1,433 pounds. Manfred Schurti and Helmuth Koinigg shared driving duties during the 1,000 Kilometers of Nürburgring on May 19, 1974. The snorkel on the rear wing support captured engine intake. They ?nished seventh overall. Porsche Archive Teammates Gijs van Lennep and Herbert Müller driving car 8 in the same 1,000-kilometer race ?nished sixth overall. Ernst Fuhrmann (in khaki slacks and blue shirt near the ?re extinguisher) was appalled by the size of the rear wing needed for handling that he ordered them painted black to be less obvious. Porsche Archive Any further racing advantage had to come from Schäffer and Mezger. For Le Mans, they cast aluminum crankcases in the interest of durability and longevity; for shorter contests, they adopted the lighter-weight production-based magnesium cases introduced with the Carrera RS 2.7. Into these blocks they fed a carefully tested production 2-liter crankshaft that provided 66-millimeter stroke. Titanium connecting rods and pistons operated inside Nikasil 83-millimeter cylinders and cylinder heads, which adopted the slightly larger valves from the 1973 ?at sixes of 2,247cc and 2,492cc displacement, along with a twin-plug ignition. “The development time was comparatively short,” Frère wrote, “thanks to the experience gained with the turbocharged type 912 engine in the type 917/10 and 917/30 cars, particularly as the 6-cylinder turbocharged engine was almost exactly half the size of the 4.5-liter version of the ?at-12. Consequently, a turbocharging installation almost identical to that employed by one bank of the ?at-12 was used.” According to Porsche’s racing historian, Jürgen Barth, “Additional combustion air volume was provided by the addition of an induction air cooler [intercooler] interposed between the supercharger [turbocharger] and the single plenum [intake] chamber. It was located approximately where the normal Carrera had its ducktail spoiler.” By the end of the 1974 season, with the single large KKK turbocharger adjusted to 1.4 bar of boost, the 2,142cc Typ 911/76 engine produced 500 horsepower at 7,600 rpm and 405 pounds-feet of torque at 5,400 rpm. With Le Mans gears, this provided 192.6 miles per hour along Mulsanne. Porsche entered four of the cars; three, campaigned by French entries, ?nished twelfth, thirteenth, and fourteenth. The factory entry with Gijs van Lennep and Herbert Müller took second overall, six laps behind a MatraSimca sports racer. This was a handful of a car. With the new engine subframe and its enormous rear wing, too much weight of the car hung behind the rear wheels. In fact, weight balance with driver and full tanks was 30 percent at the front and 70 percent at the rear. To maintain control of nearly 500 horsepower with that kind of weight bias called for uncommonly large tires riding on 10.5-inch-wide wheels at front and 17s at the rear, running, according to Barth, 245/575-15 Dunlop racing tires up front and 340/57515s in back. In an interview in 1991, Norbert Singer recalled that when Fuhrmann ?rst saw the prototype, he felt scandalized by the “airplane wing,” the Eindecker, on the back of the car. As an engine man, he wondered why, and if, such a large structure was necessary; it was, Singer assured him, especially for straight-line, high-speed stability. To minimize his own discomfort, Fuhrmann ordered Singer to paint it ?at black. Race reports from Le Mans over the June 15 and 16, 1974, suggest that Porsche’s RSR 2.1 Turbo could have won the twenty-four-hour race. Singer and his engineers determined the production-derived Typ 915 ?ve-speed transmission was up to RSR power. In an ideal world, Singer would have wanted the new, stronger four-speed Typ 930 transmission, but it was not ready. Meanwhile, Matra had asked Porsche to design and develop new synchronized transmissions for its V-12s. As part of the contract, Porsche guaranteed race support, and on Sunday morning, Matra needed it. The team’s leading driver, Henri Pescarola, pulled off to the side of the Mulsanne Straight with no gears. After some struggling, he found something that connected and he limped into the pits. At this time, van Lennep and Müller were closing on the lead Matra. Singer was there when two Matra crewmembers, arrived asking for help. The Porsche gearbox needed a rebuild, something Singer’s transmission guys could do more ef?ciently than the Matra crew. “This gave us quite an interesting dilemma,” Singer recalled. At the April Le Mans trials, the two factory RSR Turbos ran with engines developing 500 horsepower. For the June race, the car wearing No. 22 ?nished second overall behind a low-slung Matra prototype. Porsche Archive Ultimately, the decision went to Fuhrmann, who replied that Matra was a customer and Porsche must help. Singer sent two of his best transmission mechanics and they got Pescarola’s gearbox repaired in 45 minutes. During that time, the RSR took the lead. But with all the Matra’s gears working and its Mulsanne stop speed near 200 miles per hour, the RSR strained to keep up. Then its Typ 915 transmission lost ?fth gear. “It was a production gearbox,” Singer explained, “and the high power and torque were too much for it. With the Matra, our guys could rebuild the transmission while it still was in the car. We had to take the engine out to do that on our car, so it was impossible. Van Lennep and Müller had to go on with just four gears.” Running in fourth gear along Mulsanne slowed the RSR, but at the same time it improved fuel economy so much that Porsche eked out three extra laps on each tank. The car held off the second Matra and ?nished ten laps ahead of it. The rest of the year proved the strength and brilliance of the turbo ?at six. For cars that seemed outsized and overmatched at the start of the season, these production-derived race cars ?nished the 1974 WCM in third place behind outright sport prototypes from Matra and Gulf. The FIA had told entrants and manufacturers to expect Group 5 regulations in effect for 1975. Instead, the group delayed introduction for one year, giving Porsche a breather to improve its planned entries. Helmuth Bott assigned Singer to assist privateer Reinhold Jöst through the year with his 908/3 Turbo, which ?nished fourth overall at Le Mans. “That year [Jöst] did most of the World Championship races,” Singer wrote in his fascinating autobiography, 24:16, “something which gave us a lot more experience with the turbo engine. This would be the key component of all our racing cars in 1976. These were to be based on the road going 911 Turbo model which had now gone into full scale production.” Buy from an Online Retailer US: UK: Celebrate the rebirth of the world’s most stunning high-performance automobile. Porsche made history when it brought turbocharging to the racing world in the form of the 917. When strict regulations regarding engine displacement took away the option of bigger engines, manufacturers turned to forced induction. In its wildest trim, the original 12-cylinder turbocharged Porsche racing engine yielded as much as 1,400 horsepower! Porsche’s official philosophy was that racing cars must have a connection to street cars, so it was preordained that Porsche would eventually produce a turbocharged version of its air-cooled flat-six cylinder engine. The resulting 930 Turbo appeared in the spring of 1975 in Europe. Acceleration from 0 to 100 kilometers per hour took a scant 5.5 seconds, and its top speed was 155 miles per hour. The Turbo’s distinctive rear wing let the world know that this was something very special. It was nothing less than the rebirth of the high-performance automobile. At a time when the big-block engines in America’s so-called “muscle cars” were putting out 180 horsepower and the engines in exotic supercars weren’t much more ambitious, the lightweight Porsche was a genuine rocket. Porsche Turbo: The Inside Story of Stuttgart’s Turbocharged Road and Race Cars celebrates Porsche’s five decades of turbocharged supercar performance, both on the track and on the street. It covers all of the major racing cars as well as the turbocharged street cars, including the 930, 935, 924, 944, 968, 911, and Cayenne Panamera. Don’t let this one fly past you! Share article facebook twitter google pinterest If you have any comments on this article please contact us or get in touch via social media.