From 1966 to 1974, the unhinged Canadian American Challenge Cup (Can-Am) stirred innovation that has never been emulated. Can-Am’s rulebook was thinner than a political party pamphlet, enticing manufacturers like McLaren, Lola and eventually Porsche, to build ever more outrageous machines.

Porsche’s assault on Can-Am was all-conquering. Partnered with Penske racing, Porsche unseated the undisputed Can-Am champions - McLaren. Driven by Mark Donohue and George Follmer, Penske’s Porsches were envied by the paddock. Porsche’s 917 Spyders won twelve of the seventeen events they entered. George Follmer became Can-Am champion in 1972 with the 917/10. Donohue followed in 1973 with the 917/30.

To an envious competitor or jaded spectator, Porsche’s pulverisation of Can-Am looked straightforward. Mark Donohue’s fellow drivers continually grumbled at the 1972 Indy 500 champion’s ‘Unfair Advantage’. However, glancing behind the curtain of the Porsche Can-Am project reveals strife, desperation, and elbow grease. Porsche’s Can-Am successes are extensively discussed and documented. This is the other side of Porsche’s Can-Am story.

Porsche’s partnership with Roger Penske began over lunch at the 1971 24 hours of Le Mans. Mrs Piech and her sons, Ferdinand and Michael, expressed their wish to enter Can-Am as a works team and for Penske to run the cars. Following several trips to Stuttgart, Roger Penske formed an alliance between two firms obsessed by competition.

At the time, Penske had a successful alliance with McLaren in USAC. However, the British based firm refused to sell Penske one of their dominant Can-Am machines. Therefore, much to Mclaren’s terror, Penske felt no guilt in accepting Porsche’s proposal.

On the surface, the Porsche Can-Am deal was a major coup for Penske. After all, Porsche had won the previous two 24 hours of Le Mans. However, Penske’s masterful driver-engineer, Mark Donohue, spotted problems immediately. On a reconnaissance trip to Watkins Glen with fellow engineer Don Cox, Donohue quietly studied the embryonic Porsche 917-10 entered by Jo Siffert. Poor preparation, heavy suspension and an outdated subframe were a few of Donohue’s initial concerns. Donohue was also baffled that another driver had access to the car. Before Penske’s crew had taken delivery of their first Porsche Can-Am machine, doubts were creeping in.

Nevertheless, a trip to Porsche’s new Weissach facility would hopefully dispel any doubts for Donohue and Penske. Over a hearty lunch lubricated by liberal amounts of alcohol, Donohue was introduced to several Porsche figureheads. One of whom, was Helmut Flegl, who would be Penske’s main engineering contact.

More festivities followed the next day. After a photoshoot with the 917/10 Spyder, Donohue was ushered to a barbeque with Porsche staff, from shop floor to board room. Donohue’s enjoyment of the jovial occasion fuelled by generous quantities of beer and wine, was interrupted by a request to drive the 917/10 Spyder that afternoon!

Assuming the run was simply for photographs, Donohue coaxed the 917/10 around the brand new Weissach test track at a gentle pace. Despite the post lunch haziness, Donohue’s legendary instincts couldn’t ignore the 917/10’s alarmingly unpredictable manners. At 150 miles per hour, Donohue required the help of his legs to hold the steering straight. Clearly, there was work to do.

Back in the pits, Helmut Flegl was unimpressed that Donohue lapped 1.5 seconds from the lap record. To anyone other than an uncompromising engineer, such pace could be interpreted as extraordinary, considering the circumstances. Keen to sober up and conjure the attentiveness to tame this brutal prototype, Donohue asked the Porsche mechanics to adjust the throttle pedal. Thus, buying valuable time to recover from Porsche’s hospitality.

For three weeks, Donohue and Flegl grafted away on the Weissach skid pad, much to the bemusement of their colleagues who questioned this unusual technique. Curing the 917/10’s unruly handling required radical thinking. One afternoon, Donohue and Flegl retired to the office to discuss a solution to a rear suspension issue, whilst polishing off a bottle of Cognac!

On the final day of his trip, Donohue lapped half a second quicker than before. In the context of Can-Am, this was a feeble increase and Donohue knew they desperately needed to get the car to the Penske shop.

When Penske’s 917/10 arrived in Reading, Pennsylvania, the tinkering began. By December 1971, new rear wings had been fitted for the first stateside test at Road Atlanta. Despite imploding an engine, the new Penske designed rear wings proved quicker. Finally, some progress.

Further suspension developments gave Penske’s 917/10 even more speed. Donohue soon questioned whether a turbo motor would be necessary after all. However, Roger Penske was adamant that turbocharging was the golden bullet for Can-Am success. Penske proved correct, but the initial forays with the 917/10’s turbo engine were disastrous.

Penske’s crew tested the first iteration of the turbocharged flat 12 engine at Road Atlanta in 1972. Like a moody teenager, the engine couldn’t be woken on the cold February morning. Eventually, the gargantuan motor spluttered into life. However, Donohue discovered an alarmingly binary throttle pedal. In other words, 100% throttle, or nothing at all. On part throttle, this revolutionary power unit would shut off in disgust.

So, it was back to Weissach for Donohue, who was surely becoming familiar to Lufthansa cabin crews. Having convinced Roger Penske that it wouldn’t be necessary to miss the opening round of the 1972 Can-Am season at Mosport, Donohue now faced the task of cajoling Porsche’s engine team into a solution for the fickle turbo charged motor.

In Porsche’s engine lab, the penny finally dropped. Below 5000 revs per minute, the engine wouldn’t run at all. Much to his bemusement, Donohue learnt that the engine had been calibrated to run on full throttle or nothing at all. Once onto the scent, Donohue and Flegl tweaked the 917’s fuel injection until the engine played to their tune. Donohue immediately obliterated the Weissach lap record. Running nearly 900 horsepower, the ‘Panzer Porsche’ was ready for action.

Arriving at Mosport in June 1972, all eyes were on the #6 L&M Porsche 917/10. Following President Nixon’s ban on TV tobacco adverts, brands like L&M were delighted to spend big on high profile motorsport sponsorships. As usual, Penske had perfected every detail of their machine, including the paint job. Costing an eyewatering $3000, the 917/10’s paint job looked immaculate. Yet, Helmut Flegl was far from impressed, given the weight of the paint on his flyweight masterpiece! Flegl needn’t have worried. Donohue immediately eclipsed the lap record by three seconds.

Although most technical concerns had been addressed, political matters were next on the agenda for the fledgling Penske-Porsche team. Prominent Porsche dealers, Vasek Polak and Peter Gregg, were incensed that they couldn’t obtain a 917/10 like Penske’s. However, Roger Penske asserted his exclusivity to the 917/10 and reminded Porsche of the considerable effort of his team to develop this ground-breaking machine.

A valve clogged with Ontario dirt thwarted a certain debut victory for the #6 L&M Porsche 917/10. Denny Hulme took the win for McLaren, but the secret was out, Porsche’s 917/10 was the car to beat.

Unwilling to rest on their laurels, Penske’s crew travelled to Road Atlanta to test further developments. Keen to maximise testing time, Donohue hopped into an experimental magnesium 917/10 chassis and headed onto the circuit to run in a new motor. After a couple of steady laps, Donohue began to stretch the 917/10’s powerplant which pulsated under the wafer-thin bodywork, inches behind him.

Approaching 150 miles per hour on the back stretch, a deafening crack resonated around the Braselton hills. Instantly, the bodywork tore itself free from the 917/10’s chassis and sent Donohue into a tumbling cartwheel. Eventually, the wreckage came to a stop hundreds of metres down the road. Donohue incurred severe damage to his leg which forced him out of the cockpit for four months. However, without his Paul van Valkenburgh designed safety seat, Donohue believed he would’ve been killed.

Watching another driver claim the outstanding 917/10 which Donohue had toiled to create, was far more torturous for the American star than the leg pain or the drugs to numb it. Playing super sub, George Follmer won on his 917/10 debut at Road Atlanta, enjoying the luscious fruit of Donohue’s labour.

Unfortunately, the motorsport world suffers from selective amnesia. Only a fortnight afterwards his Road Atlanta win, Follmer went from hero to zero. Buoyed by their successful arrival in Can-Am, Porsche were keen to flex their muscles. For round three at Watkins Glen, Porsche charted a plane for management, guests, and journalists to travel to Watkins Glen and watch their new masterpiece annihilate the competition.

Unfortunately, another valve issue reared its head at the most inconvenient time. Follmer finished fifth and Porsche were furious. Porsche pointed the finger at Follmer and demanded that Mario Andretti or Jacky Ickx drive the car instead. Roger Penske placed blame at Helmut Flegl’s door. Donohue, on the other hand, was anxious about a new driver coming in to spoil the pot and vouched for Follmer.

With the disaster of Watkins Glen put behind them, Penske Racing and George Follmer marched on to the 1972 Can-Am series title. In the latter stages of the season, Donohue made his return from injury and won at Edmonton in a second 917/10.

At the final round at Riverside, Donohue and Follmer’s already frayed relationship eroded for good. Both Penske-Porsche men were comfortably in the lead, with Follmer ahead. However, on the pit straight, in front of the entire paddock, Follmer pulled over. On the surface, this may have seen like a noble gesture given Donohue’s efforts with their car. In fact, this was a taunt from Follmer to Donohue, who was struggling with a wheezing engine and suspected slow puncture. Donohue was later forced to pit from the lead to assess the suspected tyre issue. Follmer went on to win his last race for Penske Racing. After the race, John DeLorean branded Follmer’s conduct as having “absolutely no class”.

Dejected by Follmer’s stunt, Donohue trudged back to his motorhome. However, a sympathetic colleague appeared to cheer up the real hero of the 917/10 project. Porsche’s managing director, Dr Ernst Fuhrmann, told Donohue that he deserved the win and that they should share a drink together. A bottle of bourbon was acquired and without glasses or ice, Donohue and Dr Fuhrmann drowned away the sorrow of a disappointing end to Donohue’s season.

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Donohue claimed redemption in 1973 by pasting the field in the outrageously superior Porsche 917/30. To the casual observer, Penske and Porsche may have bludgeoned the opposition with brute force and a bulging chequebook. In fact, Donohue and Flegl’s tireless and frustrating work behind the scenes on the 917/10 was the real secret to cracking the Can-Am conundrum.