The Porsche 935 was a racing car made by German carmaker Porsche, introduced in 1976. As the factory racing version of the Porsche 911 turbo prepared for FIA-Group 5rules, it was an evolution of the Porsche Carrera RSR 2.1 turbo prototype, the second place overall finisher in the 1974 24 Hours of Le Mans.
Beginning with the 1977 season, Porsche offered the 935 to customers entering the World Championship for Makes, in the IMSA GT Championship and in the German Deutsche Rennsport Meisterschaft (DRM). The 935 went on to win the 1979 24 Hours of Le Mans overall, and other major endurance races, including Sebring, Daytona, and the 1000 km Nürburgring. Of the 370 races it was entered, it won 123.
Usually, no other make could challenge the Porsche 935, due to the availability of customer models. Each race, at the time, typically featured at least five 935s. As racing became more popular, the diversity of the marque suffered. The large turbocharger was used with mechanical fuel injection which caused turbo lag followed shortly by a fireball spitting from the exhaust and an enormous amount of power (up to 800 hp). The dominance of the 935 was ended by the FIA rules changes which came into effect in 1982, when the six numbered groups were replaced by only three groups, A, B and C.
For 1976, endurance racing had two world championships: the 1976 FIA World Championship for Makes for Group 5 special production cars, and the 1976 World Sportscar Championship season for Group 6 prototypes up to 3.0L. Accordingly, the 935 and the new Porsche 936 were the two-pronged Porsche effort for 1976. Each championship had seven races, with only Dijon hosting both on the same weekend, while on two other weekends, the races were even run in different countries, which forced Porsche to divide its resources. Jacky Ickx and Jochen Mass were the main drivers, when the F1 schedule permitted. Rolf Stommelen, who was recovering from his bad crash in the 1975 Spanish GP, was the backup, along with Manfred Schurti.
Under Group 5 rules, also known as "silhouette rules", several significant modifications were allowed (including bodywork modifications, larger wings, wider axles and water cooling), provided that the basic silhouette of the car remain unchanged when viewed from the front. The 935's engine was a 560 hp (420 kW) (at 7900 rpm) version of the regular 3.0 L flat-six, with 60 mkp (438lb-ft, 588Nm)torque at 5400 rpm. Boost was between 1.35 and 1.55 and fuel consumption was 52 litre per 100 km. Capacity was reduced to 2.85 L, and with the turbo charging penalty factor of 1.4, it fit into the 4.0 L class which had a prescribed minimum weight of only 970 kg (2,140 lb). Porsche, having a lot of experience with lightweight cars, had managed to get the Carrera RSR prototype to under 800 kg. The empty 935 tipped the scales at 900 kg, and weight distribution could be balanced with an additional 70 kg. Preseason testing at the fast Paul Ricard circuit showed a top speed of 295 km/h.
In addition to the naturally aspirated 340 hp (250 kW) Carrera RSR introduced in 1974, Porsche offered a customer racing version of the 911 Turbo prepared for the more standard Group 4 rules, the 485 hp (362 kW) Porsche 934. Some customer teams modified their 934s to Group 5 rules with body kits supplied by Porsche, these were often designated 934/5. Cologne-based Kremer Racing entered a 935 K1 built on a factory shell which in the first race, the six hour Mugello, finished second behind the Martini Racing sponsored factory entry of Mass and Ickx. Porsches occupied the first seven places ahead of a BMW in eighth, which according to the points scheme meant that Porsche had now twenty points, and BMW three. The factory 935 also scored the pole, fastest lap and win at the six hour Vallelunga, where a BMW was second and the best 934 finished fifth.
After the second race, the CSI rule makers insisted that the "whale tail" hood of the road-going 930 must fit on the race car. The air-to-air intercooler setup under the rear hood had to be altered to a more compact air-to-water layout, which cost Porsche several weeks of testing and half a million Deutsche marks.
The hastily modified 935 again won the pole and fastest lap at the six hour Silverstone, but due to a clutch problem at the start, the Martini car could finish only tenth, with the second-placed Kremer 935 collecting valuable points for Zuffenhausen. A private BMW 3.5 CSL had beaten it to the finish by a second. Even more worrisome to Porsche was the fact that BMW Motorsport had also entered a turbo, a 3.2 CSL driven by Ronnie Peterson andGunnar Nilsson. That new BMW had qualified only one second behind the factory 935, but two seconds ahead of the third placed Kremer 935. The powerful BMW did not last long in the race, however, due to gearbox problems.
Factory Porsche 935 driven by Jacky Ickx and Jochen Mass at the 1976 6 Hours of Silverstone
Initially, Porsche ran the 935 with the 911's original fender-mounted headlights, in two different guises: a sprint version with a wider version of its wheel arches, and a high speed version with modified aerodynamics. The sprint setup was rarely used. However, after carefully studying the rulebooks, Porsche engineers, namely Norbert Singer, discovered a loophole regarding the modifications of fenders that gave them the liberty to remove the headlights to reduce drag and create more downforce, to which the venting slits contribute. This "flat nose" (also known as the "slant nose") with headlights in the front spoiler, became the distinguishing feature of the 935 and was later offered on the roadgoing 930 as the flachbau, or "flatnose", part of Porsche's sonderwunsch, or "special wish" program. Also, the 935 now had extended "long tail" rear fenders, similar to the low drag setup seen years earlier on the Carrera RS. These fenders also offered more space for engine periphery and efficient cooling.
The 1000 km Nürburgring, usually consisting of 44 laps, was run in 1976 as a 47 lap 1073 km race, putting even more strain on the new Group 5 machinery. With Mass and Ickx being at the 1976 Monaco Grand Prix, Rolf Stommelen and Manfred Schurti stepped in to drive the 935 which by now had the new look it became famous for. With the help of higher turbo boost, Stommelen qualified the 935 on the pole with a stunning 7:37.5(see List of Nordschleife lap times (racing)), while the BMW turbo did not take part. The fastest of only nine race laps was just over eight minutes, though, as the engine was not sorted out, and vibrations caused ignition failure. Again, a reliable Schnitzer Motorsport-entered naturally aspirated BMW CSL took the win, with the customer 934 of Loos salvaging valuable second place points for Porsche.
The 1976 24 Hours of Le Mans counted towards neither world championship, but Le Mans was often considered the real championship. For that race, it was possible to use the 935's well-tested original engine setup. The main battle was between the sportscars, with a Renault Alpine setting the pole. The 935 driven by Stommelen and Schurti qualified third and, despite the weight and drag of a Group 5 silhouette, finished fourth overall, with one of the Porsche 936s taking the win.
At Zeltweg, Ickx was back, setting the pole, but the throttle link broke before mid-race. Derek Bell set the fastest lap in the Kremer 935, but nonetheless two BMW coupés won ahead of a private 934. Porsche still had a narrow lead in the points standings, but only the best five of the seven events would count. BMW had now three wins compared to Porsche's two, which meant that Porsche had to win the final two races. The new engine setup was tested at Weissach in a modified 934 while the race cars were shipped overseas. At Watkins Glen, the regular race chassis 002 of Mass and Ickx needed an extra stop for new pads for the Porsche 917 derived brakes, and the test chassis 001 of Stommelen and Schurti won, with the best BMW being fourth. Porsche now had three wins and two seconds equaling ninety points, which meant that only another win could add five more points to their tally. BMW had also three wins, but only one second and a fourth, equaling 85 points. Without a competitive third brand, the winner of the final round would take the world championship.
In Dijon, the turbo of BMW Motorsport was back, now with 3.5L, and this time the fast Swedes Peterson and Nilsson put it on the pole, half a second ahead of Ickx. Again the transmission was not as strong as the Bavarian Motor Works 750 hp engine, failing before the first of the six hours had passed. Three 935s plus two Group 5 spec 934/5s won ahead of the best normally aspirated BMW. The 935 and 936 had each won its championship, and Le Mans, too. The age of turbo engines had begun in endurance racing.