1973 — The 917/30 and the Limits of Freedom

By 1973, the Canadian-American Challenge Cup stood at the edge of what circuit racing could sustain. For years, Can-Am had been the last frontier: the championship where engineers were told not to think smaller, but to think faster. McLaren had defined that era with a dynasty of orange Chevrolets from 1967 to 1971. Porsche’s arrival in 1972 toppled the old order. But what Porsche and Penske brought to the grid in 1973 was not an evolution. It was the final stage of what Group 7 freedom allowed.

At the center of this transition stood Mark Donohue, returning from his 1972 injuries with the precision of a scientist and the relentlessness of a champion. His machine, the Porsche 917/30, became the most powerful road-racing car ever constructed. Its twin-turbo 5.4-liter flat-twelve could be dialed from around 1,000 horsepower in race trim to well above 1,200–1,300 horsepower when the boost knob was turned. Donohue had the discipline to use its potential without abusing it, and the series was about to learn what that combination meant.

The rest of the field prepared for a different reality. Rinzler Motoracing returned with multiple Porsche 917/10 entries for George Follmer, Charlie Kemp, and others. Vasek Polak and independent Porsche teams expanded the turbo presence. Shadow continued its DN2 programme, low, aggressive, and spectacular but fragile. McLaren, now surviving through customer cars, appeared via M20s and older M8Fs in the hands of private entrants like David Hobbs. Lola’s T260s soldiered on. All of them existed in the wake of a new gravity: whatever the 917/30 became, the rest would have to fight within its orbit.

The season contained eight rounds — Mosport, Road Atlanta, Watkins Glen, Mid-Ohio, Road America, Edmonton, Laguna Seca, and Riverside. The older 917/10s won the opening two events, but once the 917/30 reached full operating form, the series tilted permanently.

What followed was brilliance, and the end of an era.

Round 1 — Mosport Park (June 10, 1973)

Mosport, one of Can-Am’s traditional homes, opened the 1973 season with the expectation that Porsche would be strong — but not necessarily that the new 917/30 would win immediately. And that proved true. Penske and Porsche were still learning the new car, and Mosport’s first blow went to the older, more familiar 917/10.

Qualifying told the story. The front rows were filled with 917/10s — including Charlie Kemp’s Royal Crown Cola-backed Rinzler entry — while Donohue’s 917/30 hovered deeper down the order. The machine was not yet dialed in over a full race distance, and Penske’s engineers continued adjusting boost, balance, and cooling.

The race itself unfolded around the 917/10s. Kemp took the early lead and controlled pace through Mosport’s fast, high-commitment corners. Behind him, other Porsche runners found rhythm, and the McLaren and Lola entries followed at a distance.

Donohue ran reliably but not sharply. The 917/30 finished seventh — a quiet, careful day focused on gathering data rather than pushing for a result that the car was not yet ready to deliver. It was a rare moment when the most advanced machine in the field looked almost ordinary.

At the front, Kemp delivered Porsche’s first victory of the year. Hans Wiedmer finished second in another 917/10, and Bob Nagel brought his Lola T260 home third. It was a Porsche win — but not the Porsche that would define the season.

Mosport ended with the field believing they still had time before the 917/30 became unstoppable. They had one more race before that belief evaporated.

Round 2 — Road Atlanta (July 8, 1973)

Road Atlanta’s Carling Can-Am was run in two heats, with aggregate times producing the final classification. The format rewarded consistency and punished fragile machinery — a setting that still favored the well-developed 917/10.

Donohue took pole in qualifying, proving the 917/30’s raw speed even in its early state. But speed alone didn't win two-heat events. In Heat 1, Donohue won ahead of George Follmer and Jody Scheckter, both driving 917/10s. The Porsches filled every top position, with the best McLaren — David Hobbs — further down.

Heat 2 reversed the order. Follmer responded with a flawless drive, winning the second segment outright. Donohue finished second on track, maintaining pressure but recognizing that the 917/10 remained the steadier package over a pair of 45-minute contests.

On combined results, George Follmer claimed the overall victory. Donohue placed second. Scheckter placed third. Kemp finished fourth after his Mosport win.

After two races, the points table showed Porsche on top — but the early lead belonged to the older Porsches. The 917/30 had yet to begin its real campaign.

That would change at Watkins Glen.

Round 3 — Watkins Glen (July 22, 1973)

Watkins Glen was where the 917/30 arrived. The circuit’s long straights, fast sweepers, and high-commitment corners rewarded stability and power — the exact parameters Penske had been refining since Mosport.

Donohue took pole by a decisive margin, the 917/30 demonstrating its first truly complete lap of the season. Behind him, the turbo Porsches filled the top rows: Scheckter, Kemp, Haywood, and others. David Hobbs placed his McLaren M20 as the best of the non-Porsche runners, but even he admitted the gap was widening.

The race unfolded with less drama and more inevitability. Donohue led from the start, managed boost with surgical precision, and built a lead that no one could challenge. The Glen’s layout magnified the Porsche’s strengths: on power, in traffic, and in stability.

Hobbs drove brilliantly to take second, giving McLaren its best finish of the year and showing that driver skill could still elevate an underpowered car. Scheckter completed the podium in a Vasek Polak 917/10.

Donohue’s win at Watkins Glen shifted the season's balance. The 917/30 was no longer a car gathering data — it was fully online.

The second half of the season would reveal what that actually meant.

Round 4 — Mid-Ohio (August 12, 1973)

Mid-Ohio, tight and technical, seemed like a place where brute power might be contained. Instead, it showed how complete the Penske-Porsche programme had become.

Donohue took pole.
Donohue won his heat.
Donohue won the Cup race.
Donohue set the fastest laps of the weekend.

Behind him, Follmer placed second in the Rinzler 917/10 and Jackie Oliver delivered a strong run to third in the Shadow DN2. Haywood’s 917/10 followed in fourth. The top five again consisted entirely of Porsches and Shadows, with McLaren M20s and M8Fs filling positions six through ten.

The 917/30’s advantage at Mid-Ohio wasn’t raw power alone — it was driveability. Donohue’s car accelerated off corners more smoothly and consistently than anything else in the race. Where Shadows fought turbo spikes and McLarens waited for torque, the 917/30 simply went.

Mid-Ohio marked Donohue’s second straight win. It also marked the moment when the reality became unavoidable:

The 917/30 wasn’t the fastest car in Can-Am.
It was the fastest car the series had ever seen.

Round 5 — Road America (August 26, 1973)

If one track on the calendar represented everything the 917/30 was designed to conquer, it was Road America. Four miles. Long straights. Fast kinks. High average speeds. It was the natural home for a car that produced more power than a Formula One grid.

Donohue took pole by a margin that turned heads across the paddock. The 917/30 approached an average lap near 120 mph — unheard of a few years earlier. Behind him, Scheckter, Follmer, Haywood, and Kemp filled the Porsche rows, followed by McLarens, Lolas, and other independents.

The race was a demonstration. Donohue managed the early laps conservatively, then increased boost through the mid-race phase. On the long straight toward Canada Corner, the 917/30 reached speeds no other Can-Am car could approach. Yet it wasn’t reckless — Donohue always drove within limits.

Scheckter finished second in a 917/10. Follmer finished third. Haywood and Kemp followed, completing another all-Porsche top five.

Road America confirmed what everyone suspected: the 917/30 was untouchable at full flight. There was no circuit left where its advantage could be muted.

Round 6 — Edmonton (September 16, 1973)

Edmonton Speedway Park — fast, flowing, and deceptively technical — put the 917/30 back in its element. Here, the average speed across a two-hour race would climb past 110 mph, and Donohue arrived ready to secure the championship.

He took pole and immediately turned the race into a strategic exercise. Over 50 laps, he controlled pace, traffic, and boost. Behind him, George Follmer delivered a strong drive to second in a 917/10, keeping pressure but unable to challenge directly. Jackie Oliver finished third in the Shadow DN2, one of the team’s best results of the season.

Further behind, Hobbs brought his McLaren home fourth. Private McLaren runners followed in the top ten, their consistency proving valuable even as outright speed eluded them.

Edmonton underlined the technical hierarchy: Penske-Porsche, then the independent 917/10s, then Shadow, then the McLarens and Lolas. The ladder was clear. The gaps between rungs were not closing.

With his fourth straight win, Donohue placed one hand firmly on the championship trophy.

Round 7 — Laguna Seca (October 14, 1973)

Laguna Seca, shorter and more technical, theoretically offered the field a chance to close the gap. In practice, the result was the same: the 917/30 remained beyond reach.

Donohue took pole with a lap that blended power with finesse — the Porsche’s strength lay not in brute force alone, but in how precisely Donohue could meter it through Laguna’s off-camber turns. Behind him, Jackie Oliver’s Shadow DN2 and Hurley Haywood’s 917/10 formed the next strongest pairing.

The race clearly showed the gap was smaller at Laguna — but still unbridgeable. Donohue controlled the early laps, built a modest margin, and maintained it through traffic without risking the car. Oliver drove superbly to second, giving Shadow one of its strongest finishes. Haywood completed the podium for Brumos.

Though Laguna Seca’s layout reduced the Porsche advantage slightly, it still could not alter the outcome. Donohue’s fifth win in a row sealed the championship mathematically.

With one round left, 1973 now belonged completely to Porsche and Penske.

Round 8 — Riverside (October 28, 1973)

Final race of the original Can-Am era

Riverside closed the season — and the classic Can-Am era — with a race that captured everything the championship had become. High speeds, extreme strain on machinery, punishing heat, and a single car capable of reducing the field to spectators.

Donohue took pole one last time, the 917/30 lapping Riverside with an average speed hovering near 125 mph. The front rows were filled with Porsche 917/10s from Brumos and Rinzler. The Lolas and McLarens formed the midfield.

Over 49 laps, Donohue drove with careful control, protecting the car while maintaining a pace no one could live with. Hurley Haywood finished second in a 917/10. Charlie Kemp finished third. Bob Nagel’s Lola and Milt Minter’s Alfa T33/3 completed the top five.

Behind them, attrition mounted. Shadows broke. McLarens overheated. Privateers retired in clusters. Riverside remained an unforgiving place, and the 917/30’s reliability made the contrast more dramatic.

When Donohue took the chequered flag, he secured his sixth win of the season and one of the most decisive championships in racing history.

The 1973 Can-Am season was finished.
So was the era that created it.

Epilogue — Dominance at the Edge of Reason

The 1973 Can-Am season did not merely produce a champion — it revealed the limits of the concept that created Group 7. The Porsche 917/30, prepared and executed by Penske Racing, was the purest expression of unrestricted sports-car engineering ever built. With adjustable turbo boost, advanced aerodynamics, and a flat-twelve generating over 1,000 horsepower, it operated in a performance window beyond the reach of its rivals.

Mark Donohue’s driving completed the picture. His methodical approach preserved the car mechanically while extracting its potential with unmatched precision. He did not win through chaos — he won through clarity.

But dominance has costs. The budgets required to match Porsche skyrocketed. Fuel consumption soared. The 1973 oil crisis made massive turbocharged monsters less politically and commercially viable. Sponsors reconsidered investments. Teams folded or refocused elsewhere.

In the record books, 1973 is a year of statistics: six wins, eight rounds, and the most powerful road-racing car ever fielded. In history, it marks the point at which the original Canadian-American Challenge Cup became unsustainable.

The series would continue under different rules in 1974.
But the era defined by unlimited imagination ended here — with a blue-and-yellow Porsche that proved imagination had no natural limit.

Sources —

– Motorsport Magazine Archive — 1973 Can-Am race reports (Mosport, Road Atlanta, Watkins Glen, Mid-Ohio, Road America, Edmonton, Laguna Seca, Riverside)
– RacingSportsCars — Full 1973 Can-Am results, classifications, lap charts, qualifying times, and average speeds
– RacingYears — 1973 calendar, standings, and final championship table
– Porsche historical competition archives — Technical documentation for Porsche 917/10 and 917/30 programmes
– Penske Racing historical materials — 1973 Can-Am engineering notes and team reports
– Shadow Racing history — DN2 programme records and event summaries
– Track historical archives — Event documentation for Mosport, Road Atlanta, Watkins Glen, Mid-Ohio, Road America, Edmonton Speedway, Laguna Seca, and Riverside during the 1973 season