Clockwork Orange

For five consecutive Cam-Am seasons, works McLarens steamrollered all opposition by winning 37 out of 43 races and take the title every year. Story by Mark Hughes, pictorial evolution by Doug Nye.

The M8F marked the zenith of McLaren’s extraordinary run of success in the big-buck Can-Am Championship between 1967 and 1971. Rarely has a single marque dominated a top-level race series for so long and with such overwhelming force. Apart from taking all five Can-Am titles in this period, McLaren cars won 37 of the 43 races, including an incredible sequence of 19 successive victories. No wonder this motor racing legend will forever be nicknamed “The Bruce & Denny Show”…

In retrospect, it seems curious how, with such substantial prize money on offer, McLaren could have been left for so long with a near monopoly of these handsome commercial rewards. But then success breeds further success. As well as delivering sporting achievement, the Can-Am was significant as a nice little earner for the Colnbrook-based team, at a time when Bruce’s embryonic operation was struggling to make its mark in Grand Prix racing.

“Can-Am was the making of McLaren,”, recalls Teddy Mayer, now working for Penske. “It financed the growth of the company, which was then able to go into F1. It paid very well if you finished first and second most of the time, and through 1969, our best season, we were usually picking up prize money in the $50,000 – $75,000 range at each race. And then we were always able to sell the works cars for good money at the end of a season, and more came in from the customer cars built by Trojan. But it was a lot of fun too…”.

M6A Founds a Dynasty

The bedrock of McLaren’s super-successful pyramid of Can-Am cars was laid with the M6A, a new design conceived after the team’s somewhat disappointing first Can-Am season with the M1B in 1966. There had been flashes of form that year when the M1Bs, driven by Bruce and Chris Amon, led a couple of races, but Lola and Chaparral had the class cars. John Surtees (Lola) took the title, Bruce and Chris trailing in the championship standings with third and sixth places respectively, neither taking a win.

Stung by Lola’s domination, the team entered 1967 determined to do much better in the lucrative Can-Am. Robin Herd, later to become one of March’s founders, began sketching out the all-new M6A, the first car from any manufacturer to be engineered specifically for the Can-Am. Although Chaparral’s Jim Hall described it as “a common car, done uncommonly well”, the M6A was a carefully judged blend of state-of-the-art structural techniques and conventional running gear. It was designed to be light, simple and pleasant to drive.

Dispensing with the traditional tubular spaceframe chassis, the M6A was the first McLaren sports car to use a monocoque, this short but wide structure being made from panels of magnesium and aluminium held together by aircraft rivets and epoxy resin. Three fuel bags within the monocoque – one in each of the side boxes and a third in the transverse cavity beneath the driver’s knees – ingeniously delivered their 54 gallon capacity to the engine without an electric pump. One-way valves in the system allowed the fuel to wash around with the forces of acceleration, braking and cornering, so that the right-hand tank, from which the engine was supplied via a fuel collector pot and mechanical pump, was kept full.

In essence, this structure became the basic building block for McLaren’s five seasons of Can-Am supremacy, although designers Gordon Coppuck and Jo Marquart would produce year-by-year improvements. IN Teddy Mayer’s words, “Robin was responsible for this key breakthrough in showing us how to build a nice, light, rigid Can-Am chassis”. Weighing just 1354lb, the M6A would be the lightest car in the 1967 series, and nimble tool.

Since the M1B had proved itself to be a good handling car, nothing radical was attempted with the M6A’’ suspension. Top and bottom lateral links located by trailing radius rods were used at the front, while the rear featured a lateral top link, lower wishbone and twin radius rods. Unlike Lola, McLaren mounted the brakes conventionally within cast-magnesium 15in wheels, which were of a massive 13.5in width at the rear to carry the latest generation Goodyear tyres.

Through the summer of 1967, leading up to the late-season September 3 start of the Can-Am series at Elkhart Lake, the M6A was tested more extensively than any previous McLaren. Sticking to his belief that a chassis should be set up before aerodynamic factors were considered, Bruce started testing the car in naked form before the first glass fibre panels from Specialised Mouldings were added. Showing how hard he went sans bodywork, Bruce’s best first-day time at Goodwood was less than 3sec adrift of Denny’s ultimate pre-season standard of 1m 13.4s.

Helped by BRM’s lateness in delivering its new V12 engine for his 1967 F1car, 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 500 bhp 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 wee were gone after the first six laps, and there was no-one in sight…”

‘The Bruce & Denny Show’ rolled relentlessly through the calendar, taking eight 1-2 sweeps, wining the other three races and suffering only three retirements, two of them through engine problems. Michigan even saw a 1-2-3 when Dan Gurney started from the back of the grid in the spare works M8B and sliced through the field to finish third.

The M8B was dramatically different from the M8A in only one respect: it sprouted a tall rear wing mounted on struts which bore down directly on to the rear hub carriers, a configuration permissible in Can-Am but outlawed in F1. Less significant, but another M8B distinguishing feature, was the creation of large scallops behind the front wheels for improved streamlining and brake cooling. Otherwise, the new car was so similar that the spare works M8B for 1969, in fact, was Denny’s M8A suitably modified. Even Bruce’s regular M8B used some components from his 1968 M8A – one was the rear suspension lower wishbone which fatigued at Riverside and pitched him into a rare high-speed accident.

The engines, still assembled at Colnbrook but now under George Bolthoff’s care, grew slightly in size when Chevrolet came up with the 7.1 litre ‘430’ which peaked at around 650bhp and could rev safely to 8000rpm. Can-Am gossip held that McLaren was using huge engines, perhaps as big as ‘480’ but this was not so – one ‘465’ was used in practice but never raced.

“The M8Bs were the nicest cars we ever built,” remembers Teddy Mayer. “Mounting the wing on the rear uprights was the proper way to do it, because this put the load straight into the tyres rather than the chassis. This made it a really easy car to set up, and Bruce and Denny always said it had lovely handling because there were no pitch sensitivity problems – but we were only allowed to do it in 1969. Our Can-Am cars, to be honest, never handled as well after this.”

With the FIA having forced stricture wing rules on the liberal Can-Am organisers, the 1970 works cars – leaping to the M8D designation because M8C was used for Trojan’s customer build – were designed within a tighter aerodynamic envelope. Since aerodynamic devices could not be tied directly to the suspension and the wing could set no more than 80cm above the base of the chassis, the M8D featured a chunky tail section with the wing mounted between upswept tail fins. The suspension was also modified to give a 4in wider track front and rear, and more strength at the rear. To deal with Bruce’s observation that the M8B had tended to shudder when accelerating hard out of slow corners, bracing was installed from each side of the engine to the monocoque.

Bruce’s tragic death while testing the prototype M8D at Goodwood on 2 June was caused by these revised aerodynamics. The new wing’s powerful downforce, accentuated by the venturi effect of the rear deck ahead of it, caused the huge bodywork tail section to tear away from its mountings.

It was a despondent team which packed two new M8Ds for the flight to America only a week later. Bruce was gone, and Denny was still nursing tender new skin on hands which had been badly burned at Indianapolis. Dan Gurney filled the void as Denny’s team-mate for the first three races. Winning the Canadian openers at Mosport and St. Jovite, but then had to step down because of a conflict between his personal Castrol sponsorship and McLaren’s Gulf backing. Peter Gethin competently took his place, scoring one victory and a pair of second places.

But it was Denny’s season, ‘The Bear’ taking his second Can-Am title with six wins from a run of eight races once he was back to full fitness. The results don’t paint the whole picture, for McLaren’s supremacy was now being threatened by Lola and Chaparral. The M8Ds no longer had such an overwhelming advantage, and actually posted slower lap times than the M8Bs at a few circuits.

The M8F arrived for 1971, when Peter Revson replaced Gethin in the team. Although the monocoque was strengthened and lengthened to give a wheelbase stretch of 3in in the interests of more stable handling through fast corners, the car looked much the same apart from the addition of full-length aerodynamic fences along either side of the body to keep air channelled to the rear wing. There was much more power, around 740bhp, from the engines, now prepared once again by Knutson, thanks to even bigger capacity (8.1 litres) and special linerless cylinder blocks cast by sponsor Reynolds in its new 390 silicon-aluminium alloy.

The McLaren steamroller continued in 1971 with eight wins from 10 starts, but the competition was still hotting up. Jackie Stewart’s Lola T260 turning out to be a serious, but less reliable, rival as he steered it to the other two victories. Revson scored five wins to Denny’s three to take his first – and McLaren’s fifth – Can-Am title.

Giving way to Porsche

This 1971 season turned out to be the twilight of McLaren’s Can-Am domination, for 1972 shaped up a s showdown of an altogether more intense nature due to Porsche’s arrival. The German company’s tool was a turbo-charged derivative of its flat 12 917 endurance sports race, the 917/10, which would be run with works support by Roger Penske, the initial single entry driven by Mark Donohue. Unlike previous Can-Am pretenders, this car had substantially more power than the 770bhp or so which McLaren could by now tease out of its self-developed Chevy V8s.

McLaren’s response to this threat was to have Gordon Coppuck design a new car, the M8 series had reached the limit of development. His new M20 was a neater package designed primarily to concentrate more of the car’s mass within the wheelbase. As a result, some of the 79 gallon fuel capacity was housed in a tank behind the driver, while two flank-mounted water radiators – as pioneered on the F1 Lotus 72 – replaced the conventional front-end layout. Driver comfort was a useful bonus: Teddy Mayer remembers the front radiator generating such a blast of hot air the Bruce and Denny occasionally suffered scalded lips. A bellhousing between engine and gearbox lengthened the wheelbase by 2in, effectively placing the engine further forward in the wheelbase.

Although they suffered too much understeer, the new M20s, still driven by Hulme and Revson (who had been invited back when ulcer-troubled Jackie Stewart opted out of a Can-Am deal with McLaren), were not far off the pole position place of Donohue’s Porsche at Mosport’s opening round. Thanks to the Porsche losing time with induction system problems, Denny was able to give the M20 a maiden victory – but the writing was on the wall. ‘The Bear’ scored only one more win in the remaining eight races as Porsche punched home its advantage, George Follmer in a second Penske entry taking the title with five victories. Its glorious five-year reign over, Gulf Team McLaren was to pull out of Can-Am for good…

“Porsche was the only and only reason why we finished,” remembers Teddy Mayer. “To compete with them we needed a much larger budget and a more concentrated design effort. We would have had to scrap most of what we’d developed over five years and start all over again. I decided that it wasn’t viable financially, and at the same time our sponsor, Gulf, decided that Indy racing would give them more coverage – so that was fine by us”.

“We were given some money by Chevy to build a turbo of our own. We built an engine, saw over 1000bhp on the dyno, and tested it once in a car. But we knew right away that we didn’t have the resources to develop it, so that was that.”

The Trojan Connection

Besides the works cars, privateer efforts boosted McLaren’s Can-Am presence to more than half the field at most races. Unable to contemplate squeezing ‘mass-production’ cars into its busy racing programme, McLaren sub-contracted manufacture to Peter Agg’s Trojan operation from November 1964. Agg, having rescued Frank Nichols’ Elva Cars from liquidation, could offer the facilities and production expertise McLaren needed, and a long-term association was born with the first ‘McLaren-Elva’ cars.

Out of over 300 Trojan-built customer McLarens, around 60 were Can-Am cars. The way the arrangement worked was that Trojan would take McLaren’s drawings for the previous season’s cars, have patterns and moulds made, sell the cars, run a spares operation, and pay McLaren a royalty on each car made.

While a few ‘production’ models shared works designations, the gaps in the factory’s M8 suffix sequence were filled by Trojan. So it was that the 1970 M8C and 1971 M8E were Trojan’s customer variants of the M8B and M8D respectively. Going back, Trojan productionised the 1967 works M6A as the M6B for sale the following season, while the customer version of the original works M8A was described, perversely, as the M12. Into 1972, when McLaren produced the M20, Trojan’s final run of production Can-Am cars carried the previous season’s works M8F designation.

Trojan’s car satisfied demand for McLaren’s super-successful recipe, but having cars one year out of date always put the privateers at a disadvantage. On only two occasions, both in 1968, were the factory drivers ever beaten by customer McLarens.