With two Le Mans wins in their bag and the 917 no longer eligible, Porsche decided to turn their attention to highly popular Can-Am racing series in 1972. Having to make up for a considerable displacement deficit, Porsche fielded heavily modified, Turbocharged 917 Spyders. These all conquering 917/30s are still the most powerful racing cars ever constructed and maybe more importantly taught Porsche valuable forced-induction lessons. Back in Europe sportscar racing was far more regulated with a displacement limit of the top 'Group 6' class of just three litres. After Porsche's European withdrawal, privateers continued to campaign the three litre 908/3s, but their flat-eight could not match the performance of the high revving Matra, Ferrari and Alfa Romeo 12 cylinder 'F1' engines. Interested to see how far they could push the Turbo envelope, the engineers at Weissach developed a new forced induction flat-6.
Following the FIA's equivalency formula of 1.4 for supercharged engines, Porsche's new engine could not displace over 2.143 litre to remain eligible for the three-litre class. With 2.142 litre Porsche came extremely close, which they initially feared would not be enough to match the 450+ bhp of the competition as the 917/30 engine produced around 200 bhp / litre. That engine was not initially designed to take the additional stresses of Turbocharging, so with a bespoke design the new flat six could be made strong enough to survive the 225 bhp/litre required. Another problem that the engineers faced was the extreme heat produced by the single Turbocharger, which greatly hampered the performance. Taking a cue from WWII airplane design, they fitted an intercooler that would cool the compressed air going into the engine. This was the first ever application of an intercooler in a (racing) car.
Fitted in the back of a 911 RSR body, the Turbocharged engine made its debut early in 1974. Using a road going chassis, this meant the Porsche Turbo could be homologated as a Group 5 car, which did not allow for one-off racers like Group 6, but also did not have the very stringent homologation requirements of the Group 4 GT class. The new car was raced throughout the season, but the many reliability niggles showed that the engine was still very much under development. Porsche's racing philosophy of using the track to develop new technology for road cars became apparent when the 911 Turbo (Type 930) debuted in 1975. This car would form the basis of a series of highly successful Group 4 (934) and Group 5 (935) racing cars that would be used to great effect by the Works and privateers well into the 1980s. It was by no means the end of the 2.1 litre engine though and a first sign of things to come was the delivery of the powerplant to 908 racers to replace the old three-litre flat-eight for the 1975 season.
Even though Porsche never officially supported the likes of Joest and Kremer with their six cylinder 908s, the Works engineers became ever more involved as the season progressed. Before the year was over, Porsche assisted not only with the engines, but also with the aerodynamics and some of these 908s were even tested at Weissach. Porsche's involvement was by no means a secret; it was nevertheless quite a big surprise when Porsche announced they would enter the 1976 World Championship with a brand new Group 6 car. Perhaps 'brand new' was not the best way to describe the 936 as it was a combination of the 2.1 litre Turbocharged engine, a 908/3 tubular spaceframe, 917 running gear and a scaled down version of the 917/30 spyder body. Of course there was a little more to the Group 6 racer and especially the chassis was modified extensively to cope with the power increase over the 908's flat eight.
Less than a half year after the first design was penned, the 936 hit the track early in April of 1976. The use of 'off the shelf' parts certainly contributed to the quick to development. In its latest guise, the six cylinder engine now produced 520 bhp, which looked sufficient to take on the latest Alfa Romeos and Renaults. Painted flat-black, the 936 made its competition debut in the Nürburgring 1000 km race, where a stuck throttle cable slowed the car down. Porsche's day was saved as Joest's Turbocharged 908/3 took the win. Throughout the season the 936 was developed and most notably grew a large central air scoop that fed air to the fan cooling the engine block; the heads were water cooled through a front mounted radiator. Although it was by no means a perfect race, Jacky Ickx and Gijs van Lennep piloted one of the two 936s to victory at Le Mans that year. The 936 would continue to dominate the season and won every one of the remaining six rounds of the World Sports Car Championship.
Needless to say, Porsche were crowned World Sports Car Champion, but it was not the championship they were really after; that was the World Manufacturer Championship, which was contested for Group 5 cars only and was also won by Porsche with the 935. The other Sports Car championship was created to keep the other Group 6 manufacturers happy and they convinced Porsche's sponsor Count Rossi to back the German's entry for 1976. At the end of the season they must have regretted that. Porsche's sole intention for the 936 had been a win at Le Mans and for 1977 they decided to concentrate on the 'big-one' and contest the other races with the 935. With no need to race on the twisty tracks anymore, both 936s were equipped with a much sleeker low-drag body. The frontal area was further decreased by decreasing the track. The Turbocharged flat six was modified and equipped with two smaller Turbochargers for better throttle response. It was quoted at 540 bhp, sufficient to propel the car to a 217 mph top speed.
Following hot on Porsche's heels, Renault had also taken the Turbo route and countered the German's two-car effort at Le Mans with three of their A442s. These sported a Turbocharged two-litre V6 engine and they got the better of the Porsches in qualifying. Some three hours into the race it did not look any better for Porsche as one car was out and the other delayed considerably and running nine laps in arrears. Ickx was mounted in the surviving car and put in one stunning lap after another, gradually reeling in the leaders. As the sun rose on Sunday morning, the Porsche was in second, but still well behind the leading Renault. Fortunately for Porsche that was struck by mechanical problems and the Germans scored a win after one of the most remarkable come-backs in Le Mans history. It all literally looked to go up in smoke for the 936 right at the end as Hurley Haywood entered the pitlane followed by a trail of smoke. One of the pistons had failed and the Porsche still had to complete the final lap under fifteen minutes and with the plugs and injection removed from the problem cylinder, the Porsche limped to the finish.
A third evolution of the 936 was prepared for the 1978 Le Mans complete with a 24-valve engine. In qualifying this flat six produced a staggering 640 bhp, which was sufficient to qualify it on pole. In the race the Renaults proved to be much quicker and more reliable than the 'new' 936s, but only just. Of the four French cars present, only one had a trouble free run; sufficient to claim that elusive win. The best Porsche was second, slowed down by long delays in the pit. The 1978 spec 936s returned to Le Mans the following year, although it did not look to have Porsche's top priority. They did claim pole position, but the two cars were out of the race early, one with an engine failure and the other being disqualified. There was a lack of top-level Group 6 racers and that paved the way to a rather unlikely victory of a Kremer modified Porsche 935. Porsche did not return to Le Mans in 1980 with a Works car.
With only three cars constructed, none of the 936s ever became available for Porsche's loyal privateers. The Stuttgart based company rewarded that loyalty by revealing the 936's secrets to the likes of Reinholt Joest and Erwin Kremer. While Kremer initially used the plans to upgrade an existing 908, Joest proposed to build a 936 of his own. The official reading of this history is still that Joest built the car but it is far more likely that Porsche supplied a complete car. As a 'Porsche 908/80' Joest entered their car in the familiar Martini colours at Le Mans in 1980 for himself and 936 master Jacky Ickx to drive. The two experienced Porsche pilots led the race, but were dropped down the order after the fifth gear had failed. The problem was repaired and as so often had been the case, the 936 was forced to fight its way back up the leaderbord. The chase eventually brought a second place, two laps behind the winning Rondeau. This fourth 936 was raced for several seasons with considerable success in Interserie races and also claimed another podium at Le Mans. Kremer later also built or received a brand new 936.
After the 1979 season, the three 936s were retired to the factory museum and Porsche had turned their attention to modifying the six cylinder engine to use it in the Indy series. The Works entry for 1981 consisted of the new 944s, which were likely to fight for a class win, but had little chance to take an overall win, which was up for grasps as there were few serious competitors left. With the advent of major rule changes from 1982 onwards, Porsche and all others had seen little use in building a new Group 6 car. Instead they dusted off two of the 936s and equipped them with the 24-valve Indy engines. The last minute entries packed a 640 bhp punch in the race and there was little stopping them from clinching a 1-2 victory ahead of the Joest 936. It was a fitting finale to the 936's long racing career in which it scored three Le Mans wins and one World Championship; not bad at all for a hastily thrown together racer! The 936 was replaced in 1982 by the 956, which sported a brand new chassis and body, but carried its six cylinder Turbocharged engine over from the 1981 Le Mans winner.
Article by Wouter Melissen, last updated on August 01, 2012
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