Helped by BRM’s lateness in delivering its new V12 engine for his 1967 F1 car, the M5A, Bruce was able to devote more time and money than he had anticipated to the M6A’s aerodynamic development – a good investment in view of the immense power and ‘anything goes’ Can-Am rationale. He did countless 150mph tests at Goodwood with Robin Herd shoe-horned into the passenger seat taking readings from air pressure taps hitched to the bodywork, while three intensive days in MIRA’s full-size wind tunnel at Nuneaton added to the data. Some in the team favoured a Chaparral-like huge rear wing and rear-mounted radiators, but Bruce preferred simplicity. The radiator stayed at the front with an air-flow system schemed to contribute useful downforce, while the rear spoiler was tidily integrated into the body to provide good downforce with relatively low drag.
Looking for a power advantage, Bruce also decided, perhaps riskily, to bring engine preparation in-house instead of relying on outside suppliers. Working from Colnbrook, Gary Knutson assembled iron-block 5.8 litre Chevy V8s using Bartz machined Camaro crankshafts and a number of McLaren modifications. With Lucas fuel injection, power output was put at over 500bhp at 7000rpm. The transmission was a Hewland LG600.
All this intensity of effort yielded brilliant results when the two M6As were shipped to the US for the 1967 Can-Am series, which had six races compressed into 10 weeks. Running for the first time in McLaren’s definitive, eye-popping orange livery, Bruce and Denny decimated the opposition.
But for a pair of engine failures in the last race, the Stardust GP at Las Vegas, McLaren would probably have completed a clean sweep. As it was, the gorgeous M6As collected five wins (the first three for Denny, then two for title-winner Bruce), five pole positions and six fastest laps. Mosport was a most dramatic performance, for the team’s 1-2 there was hard-won. With just over a lap to go, a suspension problem sent Denny briefly off the road, folding the M6A’s left-front corner onto the wheel and bursting the tyre – but he managed to limp home to victory with clouds of smoke billowing from the tyre. Bruce, meanwhile, started 1min behind the rest of the field after a leaking "bladder" fuel tank had to be changed, but he scythed through to finish 35sec adrift of his tam-mate.
Four Great M8 Years
McLaren’s new car for its title defence in 1968 was a logical development of the M6A, but its chassis differed significantly enough to earn the designation of M8A. The main improvement was to make the engine a stressed part of the chassis structure, but the new car was also 4in lower and 4in wider. Its body bore a strong family resemblance to the M6A’s, but a flatter front wing line, more sharply raked nose and deeper rear spoiler gave a much leaner look, as well as harnessing more downforce. Chaparral excepted, the M8A was the most effective aerodynamic package in Can-Am racing.
Although the M8A, designed by Jo Marquart, weighed 25lb less than its predecessor, fuel tankage increased to 60 gallons (now all carried in two side tanks) in order to feed a thirstier and more powerful engine. Still built at McLaren by Knutson, power now came from a 7-litre aluminium-block ‘427’ Chevy, which weighed 100lb less than the previous iron-block unit, developed over 620bhp and was mounted 1 ½" lower than before. Suspension was much the same, but braking was up-rated from solid discs to meaty ventilated units front and rear.
Pre-season test work was nowhere near as exhaustive this time round. The prototype chassis did several shakedown sessions fitted with hacked-about M6A bodywork, but the two pukka cars which Bruce and Denny would race for the season were completed only days before they were due to be air-freighted to the Elkhart Lake first round, which again took place early in September, as the F1 season was nearing its conclusion.
Engine unreliability was the only flaw in another impressive season, although it accounted for only one defeat when both M8As broke at Bridgehampton with piston failure, caused by rings failing to seat properly in the bores. On top of this, humiliation at rain-drenched Laguna Seca by John Cannon’s ancient M1B – ideal wet tyres gave it the edge – meant that McLaren scored only four victories out of six, but Denny and Bruce still managed to finish 1-2 in the championship.
McLaren’s 1969 Can-Am performance with its new M8B was the most devastating of all, and came at a time when Can-Am was at the height of its popularity with 11 races packed into a season now beginning in June. It was simply a two-division championship, the words McLarens alone in the premier league. At familiar circuits, the M8Bs were typically 2-3sec a lap quicker than the previous year, so that, in Bruce’s words, "…in most of the races we were gone after the first six laps, and there was no-one in sight…"
