Is this the greatest racing car of all time?

Some cars have scored more victories. Others have had longer careers. But few - if any - can match the impact of Porsche's first Le Mans 24 Hours winner, the 917.

Being the greatest in anything means more than just numbers. How do people feel about something? How did it move the game on? Does it still stop people in their tracks?

The 917 wasn't just a milestone car for Porsche, it was a seminal machine for motorsport.

The project, started in 1968, ended up encompassing many new motorsport technologies or cutting-edge ideas, from drilled brake discs to turbocharging via the use of exotic materials. There also can't be many cars that have essentially been banned from two international categories.

Before success, a big hurdle often needs to be overcome - essential for a good hero story - and the 917 had that too. Aerodynamically unstable when it first appeared, it gained a fearsome reputation early on: way faster than anything else but too much of a handful. When that was overcome, the car defeated rivals from Ferrari, Alfa Romeo and Matra, only to be outlawed by the introduction of three-litre world sportscar regulations for 1972.

Porsche then teamed up with Penske to switch to Can-Am, but perfecting turbocharging proved a tough challenge. The project came close to being postponed before a late breakthrough allowed George Follmer to steamroller the opposition, including the hitherto dominant McLarens.

The 917/30 and Mark Donohue perfected the theme, creating arguably the ultimate unrestricted race car, in 1973. It was so good Can-Am forever turned its back on the unlimited ethos that had made it so special in the first place.

Fifty years since the 917 appeared, here's our tribute to one of motorsport's true legends.

Stepping into the unknown

Porsche had largely been restricted to class wins in sportscar racing in the 1950s and 1960s, punching above its weight with small-engined machines. The move to three-litre/five-litre sportscars in the world sportscar championship for 1968 brought the small German company to the forefront and the 907s and 908s were race winners, but Porsche lost the title - and, crucially, Le Mans - to JW Automotive's ageing Ford GT40s.

When the FIA reduced the number of cars needed to homologate a model into the five-litre Group 4 category, Porsche's Le Mans-obsessed Ferdinand Piech saw an opportunity.

In just a few months, and in secrecy, Porsche designed and built 25 4.5-litre flat-12 racing cars, and the 917 was unveiled to the world at the Geneva Motor Show in March 1969.

The car followed Porsche's low-drag, lightweight philosophy, with a 1.3mm glassfibre skin bonded to an aluminium frame. The engine had been given the type number 912, the same designation for Porsche's four-cylinder 'sub-911' road car, to throw people off the scent.

Strictly speaking it was a 180-degree V12 - the pistons were not opposed as in a flat 'boxer' engine because the connecting rods shared the same crankshaft journal - and one of the keys to the engine's success was the central drive from the crankshaft and a new lubrication system, which helped reduce vibration and save weight.

The engine had to be installed at a particular angle, estimated to be around seven degrees, and three or four people were needed to get each engine aligned in the car. All parts were ordered off the drawing board and in the first tests the air-cooled engine produced 540bhp.

Power was not the problem. But instability was, and all the drivers complained as soon as the 917 hit the track at the Le Mans test day in April. The cars were so fast that they were entering a realm unexplored by racing cars and were starting to lift off the road.

Earlier Porsche long-tails had sometimes shown worrying high-speed handling traits, but the extra power of the 917s brought the issue into sharp focus. Windtunnel work had been conducted, but the aim had been to minimise drag - downforce was not yet the designers' obsession.

With the highly competitive three-litre 350bhp 908 also on its books, Porsche found it difficult to get drivers enthused about the new 4.5-litre monster.

"You had to know what you were doing. Everything about it was beyond what most people were capable of getting to" Vic Elford

In practice at Spa in May, lead driver Jo Siffert lapped 6.7 seconds faster than the best 908 in the new 917, but chose to drive the 908 in the race. He and Brian Redman won, while Gerhard Mitter/Udo Schutz failed to finish in their 917. It was easy to miss a shift and over-rev the engine, though some felt Mitter did it deliberately to avoid driving the car in the wet on such a difficult circuit.

At the fearsome Nurburgring, Porsche couldn't persuade its drivers to take on the 917 challenge and BMW stopped Hubert Hahne and Dieter Quester from doing so too. The intrepid Australian Frank Gardner and Brit David Piper stepped in and brought the car home eighth. Siffert and Redman won again in a 908.

The high-speed Le Mans circuit was much better suited to the 917. Porsche's primary aim was to win the 24 Hours, but it attracted a lot of criticism when privateer sportscar driver John Woolfe lost control of his 917 on the first lap and perished in the subsequent crash.

The two lead 917s fared better, at least to begin with. Rolf Stommelen scored a storming pole position and Vic Elford/Richard Attwood nursed their example to within three hours of victory before the bell-housing cracked. Porsche's mammoth onslaught again lost to JWA's GT40, a car conceived five years earlier.

By the end of the season the 917 had racked up its first major victory - at the Osterreichring - but the car's inherent instability remained. Many thought the chassis was flexing. Porsche wanted to push on with development, but also decided that getting someone else to run the cars at the circuit might be a good idea. It approached JWA.

The crucial test at Zeltweg has become famous - and somewhat controversial, as people from both JWA and Porsche claim credit for the subsequent breakthrough. JWA's John Horsman was certainly key in solving the aerodynamic problems - spotting the lack of dead bugs at the rear, indicating a lack of airflow there - but Porsche had also brought aluminium sheets with the expectation that bodywork changes would need to be tried.

Porsche bringing the open 917 PA Can-Am car, which had a higher tail and the drivers preferred, also pointed the way to the solution. The outcome was a higher rear-end and a more stable car.

"After three laps I had shed four seconds," recalls driver Kurt Ahrens Jr. "We knew that was what Porsche would have to work on. Aerodynamics was the crucial point."

The new 917K (kurzheck or short tail) body shape appeared for the start of the 1970 season, just in time to meet Ferrari's own five-litre sports-racing powerhouse, the 512S.

Faster than Formula 1

JWA made several changes when it received the cars, including strengthening certain areas and using flexible piping to carry the oil, rather than the chassis tubes. There was even a small use of carbonfibre lattice.

Porsche's computer was used to set up the differential and gear ratios and the 917 was slightly lighter, and a bit more powerful, than its Ferrari rival. With the aerodynamic problems solved, the 917 became the car to beat for the next two seasons.

Although much-improved, the car wasn't easy to get the best out of, such was its performance.

"The K wasn't easy to drive, but it wasn't that difficult," reckons Elford, who drove all versions of the 917. "It needed respect because it was very powerful. It wasn't twitchy, but you had to know what you were doing. Everything about it was beyond what most people were capable of getting to."

There was also internal politics. JWA boss John Wyer was unimpressed to see a factory-tended 917K, running under the Porsche Salzburg banner, arrive at the Daytona 24 Hours season opener, for Elford and Ahrens. The Salzburg team, and the Martini squad in 1971, was essentially a second works team, Piech using it to keep JWA on its toes as well as running new developments if Wyer didn't want them.

JWA's Pedro Rodriguez and Leo Kinnunen, joined by Redman, won Daytona, but Sebring was a disaster. Porsche brought a new design of front wheel hub that hadn't been fully tested. JWA fitted them, but the hubs failed, contributing to Porsche losing the race to Ferrari and - perhaps more importantly - making Wyer a little less enthusiastic about bolting on new parts.

After Rodriguez's famous virtuoso wet-weather performance at Brands Hatch, a new 4.9-litre engine arrived at Monza in April. It provided extra torque and 20bhp more power, but sprung an oil leak in practice, so JWA decided to revert to the 4.5-litre. At which point, the engine was offered to - and accepted by - Porsche Salzburg for Elford/Ahrens. They duly led, only to be thwarted by a puncture and related damage, leaving Rodriguez to pull off another fine victory ahead of a Ferrari 2-3-4.

A similar thing happened at Le Mans. JWA decided against the new long tail, Redman still regarding it as insufficiently stable, only to see Elford storm to pole in the car in Porsche Salzburg colours, though in truth there was little to choose between the 917L and 917K on lap time.

The 917 vs 512 duel was perhaps at its peak point. Porsche-Ferrari-Porsche-Ferrari-Porsche-Ferrari-Ferrari-Ferrari-Ferrari-Porsche-Porsche-Porsche-Ferrari was the look of the grid, immortalised by the film Le Mans, with the best of the rest being a works Matra MS650 in 14th, 12.4s off pole. Remarkably, the eventual winning car of Richard Attwood and Hans Herrmann qualified even slower, but survived a race of attrition to take Porsche's long-awaited first Le Mans win.

Despite his own car's failure, Elford picks out the 1970 24 Hours as one of his best 917 moments.

"It was the ultimate Le Mans car," he says of the 917L. "The first couple of times down the Mulsanne Straight I thought it was a lot shorter! At the kink I was doing over 240mph, and the first couple of times I was lifting a little bit. I convinced myself it was going to be flat-out and it was.

"When I came out the other side it was easy - I'd not changed the attitude of the car at all. With a lift I had been changing the balance of the car, when I went without lifting it was glued.

"It rained a lot that year and I was flat-out through there in the rain and the dark with no problem. That's probably my ultimate 917 experience."

A lap time comparison with Formula 1 underlines just how fast the five-litre sportscar monsters were in 1970. At Monza, Elford's fastest 917 lap in the 1000Km was 0.4s faster than the best lap that would be set in the Italian Grand Prix four months later, while Rodriguez's 3m16.5s during the Spa 1000Km was a remarkable 10.9s faster than March driver Chris Amon's fastest time in the Belgian GP. The more agile F1 cars were quicker at Brands Hatch and Watkins Glen, but even there the margin was never large.

More motorsport exploration

Early on in the project, it had been announced that three-litre regulations would come into force in 1972, but Porsche pressed on with development on multiple fronts throughout 1970 and '71.

Partly that was because of the remarkable pioneering momentum and drive Piech's team in Zuffenhausen had, and partly it was due to Ferrari. In the 1970 season finale at the Osterreichring, Jacky Ickx had outpaced the 917s in the new 512M. Faulty electrics handed the race to Porsche, but victory in the non-championship Kyalami 9 Hours underlined the speed of the new Ferrari.

Both Porsche and JWA continued working on different aerodynamic improvements, the engine was stretched to five litres and there was even experimentation with anti-lock brakes and a sucker system utilising the engine's cooling fan, though neither was ever raced. As was the norm for the time, the wheels and tyres grew larger too - punctures were not uncommon as tyre technology moved on rapidly.

Some drivers complained of spongy brakes and Porsche developed the brake discs extensively during the 917's life, but Elford recalls the car being superior to its competition in this area.

"I never had any trouble with brakes," he says. "They were always outstanding.

"I only did it in practice or qualifying a couple of times, but at Le Mans in 1970 at Mulsanne Corner, when you were coming down from 240mph I could brake at about 270 yards. Nothing could get even close."

Porsche pioneered drilled brake discs on the 908/3 (successfully used instead of the bigger car at the Targa Florio and Nurburgring) and 917, underlining that the team was at the cutting edge of racing technology.

Elford also gives a fine example of how far the car's handling had come by the Buenos Aires 1000Km, which opened the 1971 season: "Pedro and I were having a really great race. There was a pretty fast right, a pretty fast left, a long straight and then a 180-degree right-hander a bit like the Parabolica at Monza. I could close just a bit, but not enough to go by.

"Eventually I thought I'd try the outside [into the right-hander]. I made to go to the inside, Pedro moved a little bit to close the door and I went to the outside. Because he was a gentleman he gave me room and I was able to drive around the outside of him on this 150mph corner. I don't think either of us would have wanted to do that in any other car."

By Le Mans, Porsche had come up with the final iteration of the long-tail, which the drivers considered stable enough that even Wyer agreed to run two. The three examples qualified 1-2-3, but all three retired. Porsche nevertheless scored a 1-2, with the winning Martini 917K of Helmut Marko and Gijs van Lennep sporting a lightweight magnesium alloy chassis.

Interestingly, despite Rodriguez's pole being 6s quicker than the 1970 best, Elford doesn't feel the 1971 long-tail was significantly better: "When I went back in 1971 I didn't feel any difference. The top speed and handling felt the same."

But Jackie Oliver, who went even faster on the Le Mans test day, believes the 1971 long-tail was so good it could have been run at other venues, such as Spa or Monza.

"I spoke to John Horsman and he said John Wyer was never very happy with the long-tail car - he wasn't even happy that it went to Le Mans," recalls Oliver. "The long-tailed car would have been absolutely phenomenal at Spa. Maybe Wyer thought the cars were competitive enough. But it's a shame that it never ran anywhere else except at Le Mans. The balance was perfect."

The result of the 1971 Spa 1000Km probably reveals why Wyer didn't feel the need to take the risk. Rodriguez/Oliver led home Siffert/Derek Bell in a formation finish, four laps clear of the field...

By the end of 1971, the 917 had racked up 15 world sportscar championship race victories, including two Le Mans wins. The regulation changes for 1972 meant Porsche had to look elsewhere to continue the project, but Piech already knew where the 917 was headed.

Blowing Can-Am apart

There had been talks with Wyer about a Can-Am programme for 1971, with the aim of being a more serious assault in 1972. Relations between Piech and Wyer, however, were always strained and the deal didn't happen. Siffert ran an open normally-aspirated 917 (pictured above), loaned by the factory, to fourth in the championship, but McLaren remained the team to beat.

As Porsche's attention was beginning to turn to Can-Am, it had found itself facing a modified 512M in selected 1971 world sportscar championship races. Penske's blue Ferrari appeared at four rounds and outpaced the regular 917Ks every time - only at Le Mans did it struggle against the special long-tails.

Clearly impressed, Porsche did a deal with Roger Penske, and ace driver-engineer Mark Donohue and Penske's Don Cox joined the Can-Am programme. They would prove crucial in persuading Porsche that bigger was better when it came to wings and downforce, a very different philosophy to that which Porsche had begun the 917 project with in 1968-69. The Penske team, with its knowledge of US tracks and wider tyres, also made changes to the suspension geometry and pick-up points.

"Norbert said, 'How much power would you like?' I said I didn't mind so he said, 'How about 1250bhp?'" Vic Elford

The big technical challenge was developing turbocharging for road racing. Porsche knew it had to find more power to match the ever-bigger American V8s in Can-Am and, after experimenting with a 16-cylinder unit, it chose the forced induction route.

Turbocharging brought new problems, chiefly dealing with the heat and throttle response. Blowing the five-litre flat-12 gave high power straight away, but harnessing it was another matter. Two smaller turbos (as opposed to one large one) and a pop-off valve helped things slightly, but once the engine was in a car it struggled to even start. And when it did run, the throttle was like a switch, with a time delay.

An engine was shipped to Penske early in 1972 but it proved troublesome before blowing up, and Donohue flew to Weissach to help solve the problems. The American provided the spark of the answer to the starting problem - to run the engine normally aspirated.

Testing without the boost at idle and mid-range, with different throttle levels, provided lots of data that Bosch then used to find the right settings for the fuel injection pump - essentially making the engine run leaner at low boost pressures. Suction-operated valves were also added to suck in air at low manifold pressures.

Now Porsche - and Penske - had a 900bhp five-litre engine that would start and was relatively driveable. Combined with various other developments, including beefier brakes, the new open-bodied and bewinged 917/10 was ready to take on McLaren in Can-Am.

A sticking manifold pressure valve delayed poleman Donohue in the Mosport opener and allowed Denny Hulme's McLaren to win, before the project suffered a major blow when Donohue had a huge crash in testing at Road Atlanta when the rear bodywork flew off. Donohue survived but was forced to miss several races and Follmer was thrown in at the deep end with the new turbo car.

With Donohue's help, Follmer rose to the task. He narrowly missed pole at Road Atlanta, took a fortuitous victory on race day, and Hulme won again at Watkins Glen in an impressive McLaren showing, but thereafter it was almost all Porsche. Follmer won four of the remaining six rounds - with the returning Donohue also taking a victory - to comfortably become champion. McLaren withdrew from Can-Am.

The 917/10's handling was never brilliant, however, and Porsche pressed on with building a new car. The 917/30 would be the ultimate iteration, with better aerodynamics, a longer wheelbase and 5.4-litre turbo capable of producing 1500bhp but normally run at 'only' 1100bhp.

Even the combination of rising star Jody Scheckter and a turbocharged 917/10 was incapable of truly challenging Donohue and the 917/30. Donohue took pole at the Mosport opener by 1.7s in a Porsche 1-2-3-4-5. An off in traffic cost Donohue the race (won by Charlie Kemp's 917/10) and he suffered a fuel valve failure at Road Atlanta (won by Follmer's 917/10), but he won the remaining six rounds.

Such was the Porsche domination (during an oil crisis), that fuel consumption rules were introduced for 1974. Porsche might have been able to meet even that challenge, but got the distinct impression it wasn't welcome.

No-holds-barred Can-Am was over.

The 917 continued to enjoy success in the lower-level European Interserie but 1973 was the zenith of the programme. In Peter Morgan's book, Porsche 917: The winning formula, long-time Porsche engineer and race manager Peter Falk said: "I think the 917/30 was really the best racing car we ever built. Better than all the cars that followed, even the 962."

Looking at the cars, it's easy to suggest the 917/30 wasn't really the same model as the early coupes, but Elford disagrees.

"The only difference was colossal power and speed," says Elford, who made an Interserie appearance in the factory's experimental 917/30 at Hockenheim in 1973, run by Norbert Singer, to liven up a series that was being dominated by the 917/10s of Kinnunen and Willi Kauhsen.

"I'd never driven a turbo car before and hadn't raced for a couple of years so we had a test at Weissach. I felt instantly at home, it was just so beautiful.

"Norbert said, 'They keep on turning the screw up, how much power would you like?' I said I didn't mind so he said, 'How about 1250bhp?'

"It was tricky at the chicanes at first because I guess the delay in the reaction time of the turbo was about 0.2s and at 150mph you go a long way in 0.2s! That took a bit of getting used to."

Elford took pole and won. He had already mastered left-foot braking so had a novel approach to starting the race: "I asked Norbert, because of the delay, if I could keep a foot on the brake and a foot on the throttle, to keep the turbo pressure up. He said other drivers hadn't liked that but that I could try.

"So at the start I had my left foot on the brake and the throttle flat on the floor. The moment the flag came out all I did was take my foot off the brake and was about 50 metres ahead by the first corner.

"I took the [pre-chicane] Ostkurve in third and was changing up on the exit at 150mph. If I chose I could leave two black marks down the road -that's how much power there was. It was probably the most exciting car I've ever driven, and not in a bad, dangerous way. As long as you were careful and knew what you were doing it was wonderful to drive."

So what was Elford's favourite version? "All of them," he fires back. "Even including the first nasty monster because it was so much quicker than anything else. We never had to 'race' against anything. We simply waited until we drove around the next corner and then drove past."

Its place in history

To top off its record the 917 had one last hurrah in August 1975. Dusted off, Penske's 917/30 set a closed circuit land speed record at Talladega, more than six years after the original car first appeared.

In that time motorsport had changed a great deal. Just comparing the nose of the high, soft-edged original 917 to the lower, squarer version of the 1971 Le Mans long-tail demonstrates the aerodynamic strides.

The 917 was at the vanguard of an era before ever-tighter restriction started pushing designers to pursue marginal gains. Its impact on Porsche is almost immeasurable, setting off a sequence of success at Le Mans that still leaves the marque well clear on the all-time wins list. The 936 that won the 24 Hours three times was closely related to the Can-Am 917.

The 917 also left a big legacy beyond the sport. Porsche used much of the knowledge gained through the project in its road cars, particularly in the areas of lightweight materials, brakes and turbocharging.

Porsche car collection manager Alexander Klein agrees the 917 represents a special time in motorsport history.

"In its era it was the car," he says. "The period was colourful, racing was dangerous and it was a car that doubled the horsepower of its predecessor. We reached speeds that had not been reached before. It was a step into a new era. It was the first time that, without aerodynamics, nothing worked anymore."

The extraordinary sight and sound of the 917 in all its forms also adds to the legend, giving the car a higher status than its mere numbers - impressive as they are - suggest.

Porsche's own 956/962, the 1988 McLaren MP4/4 and the Ferrari F2004 were better racing cars, but the 917 is the greatest.

This week's Autosport magazine is dedicated to a special celebration of the Porsche 917, the car that launched Porsche as a Le Mans force and killed Can-Am