How Porsche's 'accidental' turbo breakthrough was pivotal in the history of Le Mans

The turbocharged engine first triumphed at the Le Mans 24 Hours in 1976, and has done most of the winning at the French enduro since. Only eight victories have gone to normally aspirated powerplants over the past half century and two of those, notched up by the V10-engined Peugeot 905, came in years when the rulebook effectively dictated that an unblown unit should win.

But the supremacy of the turbo didn’t result from some kind of grand plan. Rather, it was born of expediency. 

The Porsche 936 Group 6 prototype was the first turbocharged Le Mans winner. It was a hastily conceived and built machine to give the German manufacturer the best chance of another victory at a race it had already won twice with the 917, in 1970 and 1971.

The reason it had a turbo flat-six? Because there was an engine of that configuration under development for the Group 5 silhouette rules that came into force in 1976 – and it had nothing else suitable. 

Even when Porsche dominated sportscar racing from the start of the Group C era in 1982 with the 956 and the long-wheelbase 962 version that followed, the use of a turbo was the only option. It simply carried over a new flat-six that had won Le Mans in the final factory iteration of the 936 in 1981.

The seeds were sown for a first win for a turbo engine at Le Mans at a Porsche motorsport strategy meeting at the end of the summer of 1975. Development of the 935 Group 5 racer, due to start racing after a one-year delay in the introduction of the class, should have been top of the agenda. But, recalls 935 project chief Norbert Singer, board chairman Dr Ernst Fuhrmann had other ideas. 

Fuhrmann, here with Jochen Mass, was key to the 936 project

Photo by: Rainer Schlegelmilch / Getty Images

“We talked about the 935 and our plans for the World Championship of Makes that was coming up,” recalls Singer. “Then, suddenly Dr Fuhrmann said, ‘What do you think of the new Group 6 regulations?’ Nobody had actually read them, not in the way you would if you were building a car, but the bigger question was whether we could actually do another project alongside the 935. We told him we didn’t have the capacity.”

Fuhrmann didn’t like what he’d heard, recalls Singer: “He told us, ‘You tell me that we have all this stock of 917 parts – suspension and gearboxes – and we have the engine, it is there, so you just need to make a new frame and some bodywork. What is the problem? I tell you, we will do it.’”

The engine programme was well advanced. Porsche had been working on a single-turbo, two-valves-per- cylinder, 2.1-litre flat-six for some time, building on the experience of blown engines from its 917 Can-Am effort. It had taken two experimental 911 RSR Turbos to Le Mans in 1974 running in the prototype class.

So hurried was the development of what became the 936 that it didn’t even have a name to begin with

It was the first appearance for a turbo at the blue riband enduro although, of course, forced-induction machinery had form there: Alfa Romeo and Bugatti had won Le Mans with supercharged cars in the 1930s. Porsche didn’t go with the pair of RSR Turbos thinking it could win, though it came away with a distant second place for Gijs van Lennep and Herbert Muller. 

Singer concedes that Fuhrmann was correct in his assessment of the sportscar landscape at a time when there were about to be two world series, the WCM for Group 5 cars and the World Sportscar Championship for Group 6 machinery.

“He was absolutely right because a prototype was the better option for Le Mans,” he says. “Maybe the 935 could be as fast as the 936, but it had a much smaller fuel tank [120 versus 160 litres]. It would have to make more pitstops, so if both cars had no problems the 936 would always finish ahead.”

Porsche’s 2.1-litre flat-six engine made history during 1976

Photo by: Rainer Schlegelmilch / Getty Images

So hurried was the development of what became the 936 that it didn’t even have a name to begin with. Longtime Porsche designer Horst Reitter asked Singer, who headed up the project for the first couple of months before Helmut Flegl took over, what he should write at the top of his drawings.

They settled on 917/50 courtesy of the carry-over from its predecessor, before it was decided that 926 should be the name of the new car. 

Common sense prevailed in the run-up to the season when Helmuth Bott, under whose remit motorsport fell as head of research and development, intervened. “Mr Bott decided it was too complex,” recalls Singer. “He said, ‘We have a Group 4 car and call it the 934 and we have a Group 5 car and call it the 935. Calling our Group 6 car the 926 doesn’t make sense.’ So we decided on 936.” 

There was no confusion in the outside world because the car was being developed in secrecy. Stories that even company founder Dr Ferry Porsche didn’t know about it aren’t quite right. He turned up in the workshops one day asking for a peep “at the top secret that I am not allowed to see”.

It was his idea to paint the car black for its initial test runs and then its first race appearance at the Nurburgring in April 1976. 

Porsche wanted to surprise Renault, which would be making its own assault on Le Mans with a turbo. The French manufacturer had joined forces with sports and racing car constructor Automobiles Alpine after taking a majority stake in the Dieppe-based company.

The Alpine challenge was strong but wilted at Le Mans in 1977

Photo by: LAT Images

A two-litre normally aspirated V6 had been developed by Gordini, another marque to be subsumed into the Renault empire, with funding from Elf for an attack on the European 2-Litre Sportscar Championship from 1973. A single-turbo version of the four-valve engine then came on stream for a world championship campaign from 1975.

The ruse wasn’t needed. Renault had opted to miss Le Mans, a non-championship race, in 1975, and turned up in 1976 with a single car. New Renault competitions boss Gerard Larrousse, who created Renault Sport out of a merger of Alpine’s racing division and Gordini, knew the A442 entered for Jean-Pierre Jabouille/Patrick Tambay wasn’t a genuine contender.

“We were there to learn and gather information,” he says. “We had little experience of Le Mans, so it was too early to think about winning.”

Ickx then began the greatest comeback drive in the history of the race, hauling a car that had dropped to 41st position after early delays to the top of the order

Jabouille put the Alpine-Renault A442 on pole by a whopping 6.7 seconds ahead of Jacky Ickx in the best of the two 936s and a further 2s ahead of the solo factory 935 qualified by Rolf Stommelen.

The race, though, was a Porsche walkover. The 936 driven by Ickx and van Lennep would win by 11 laps – down from the 16 by which it had led at one point – on a day when Alpine took an early bath with piston failure shortly before halfway. 

A year later, the 936, now with twin-turbos, made it two out of two with Ickx again at the wheel of the winning car. Not that he was meant to be. The car the Belgian was listed to drive with Henri Pescarolo went out early after an over-rev, which resulted in a swap to the second Porsche prototype entered for Hurley Haywood and Jurgen Barth.

Ickx’s great recovery drive in 1977 brought the 936 its second Le Mans win

Photo by: Motorsport Images

Ickx then began the greatest comeback drive in the history of the race, hauling a car that had dropped to 41st position after early delays of its own to the top of the order. All three of the factory Alpines retired with engine failure.

Much has been made of Ickx’s heroics, which resulted in him losing a reputed 4kg, in putting the French cars under pressure, but there was an inherent weakness in the Renault engine: the same piston failure put each of the cars out.

Which is the same problem that the winning Porsche had at the end: the technically savvy Barth, who ran Porsche’s customer racing department, finished with one of the six cylinders blanked off.

Renault, now concentrating on Le Mans to the exclusion of a world championship campaign, gained its revenge in 1978. It again had the faster car but it was now reliable. It had ramped up its test programme, both on the bench and on the track.

There was a new active dyno, what Larrousse calls “the test bunk”, that allowed it to simulate a lap of Le Mans – or rather hundreds of laps – and a trip to the USA for high-speed running. 

“We went to the Transportation Research Center in the middle of nowhere [in Ohio], which gave us the chance to drive at top speed as long as we wanted,” remembers Larrousse of the trip to the automotive proving ground incorporating a 7.5-mile oval.

Future Group C engine powered Ickx/Bell to a dominant 1981 victory

Photo by: Motorsport Images

There were revisions for 1978 to the engine and gearbox, as well as the distinctive bubble cockpit of the B-spec version of the A442. 

Didier Pironi and Jean-Pierre Jaussaud gave Renault the victory it craved and allowed a switch of focus to the Formula 1 programme that had gone live in 1977. But the turbo kept winning at Le Mans.

The German Kremer team’s latest take on the 935, the K3, took the honours in 1979 when the 936s, retrieved from the museum thanks to sponsorship from Essex Petroleum, retired.

When the factory returned with the 936 and claimed a third victory for the car in 1981, it was with a 2.6-litre version of a new four-valve flat-six Porsche developed for Indycar racing. This engine would power the 956 and 962.

Again Porsche didn’t have much choice. “We started the Group C in the summer of 1981 and we wanted to race the next year,” explains Singer. “Making a new race engine would have taken one and a half years.”

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1976 was a walkover for Porsche, the Ickx/van Lennep 936 winning by 11 laps

Photo by: Motorsport Images