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McLaren Can-Am Cars

ABOVE Bruce McLaren at the wheel of his M8B, powering it through a left-hand bend at Laguna Seca in 1969; he won the race.

 

Reprinted from The Car Volume 6 Part 68 - 1985

In 1966, the debut year of the Canadian American Challenge Cup series - the Can-Am for short - Bruce McLaren's M1B sports cars were outclassed by their more powerful Lola and Chaparral opposition. In 1972 the M20s lost out in the power stakes to Roger Penske's brutally fast turbocharged Porsches. In the intervening years, however, the Can-Am was McLaren. The orange cars from Colnbrook notched up 38 victories, while privateer cars accounted for two more. Even in that final year of eclipse the works cars won twice and a private example once, bringing the final marque tally to an incredible 43.

McLaren himself won the Can-Am title in 1967 and 1969, while team-mate Denny Hulme won it in 1968 and salvaged something from the team's distress by taking his second title in 1970, the year in which Bruce was killed testing an M8D. Hulme's 1971 team-mate was colorful American Peter Revson, who took the title in the M8F.
When McLaren began planning a replacement for the amazingly successful M6A at the end of 1967, the Can-Am had already been dubbed 'The Bruce and Denny Show'. In that year's six-race series Hulme had achieved a hat-trick and Bruce a brace of wins, only 1966 champion John Surtees in a Lola getting a look in at the Las Vegas finale when the McLaren steamroller ran into trouble. If the opposition had been trampled into the dust in 1967, it was a case, in American parlance, of 'you ain't seen nothin' yet' for 1968.

Delays with delivery of the BRM V12 engine for McLaren's 1967 M5A GP car had allowed the team to concentrate almost exclusively on the M6A, which was consequently tested exhaustively. McLaren had grown eminent in GP racing in 1968 with the Cosworth-powered M7A, but the M8As weren't quite so race worthy although they had still done 500 miles (805 km) running. Similar in concept to the M6A with bathtub monocoque chassis, the M8A was four inches (10 cm) wider and comprised a full monocoque using aluminum and magnesium panels bonded and riveted to steel bulkheads. Its engine was now a stressed member supported by tubular framework and where the M6A had used 5.8-¬litre Chevrolet V8s with 520bhp, the M8A went the whole way with 7-litre unit, developed by Gary Knutson. These gave 620bhp, transmitted to the road via a Hewland LG600 gearbox to 15-inch (38 cm) wide Goodyear shod rear wheels. The suspension followed M6A practice with upper and lower lateral links and trailing radius arms at the front and a lateral top link, lower wishbone and twin radius arms at the rear, all allied to outboard coil spring damper unit. Solid disc brakes were replaced by ventilated units all round.

Start with two M8Bs on the front row

A typical grid in 1969, with McLaren (4) Hulme (5) at the front

McLaren in full flight in the Monterey Grand Prix, California, in 1968

In its first race - Elkhart Lake, Wisconsin on 1 September the M8A romped away, Hulme leading McLaren home in a convincing display that set the opposition quaking, especially as Hulme broke a rocker arm part way through and finished on seven cylinders...

At Bridgehampton they led again, and although they were sidelined by engine problems, American Mark Donohue (later to play such a significant role in McLaren's eventual Can-Am eclipse) won for Roger Penske in an M6B. At Edmonton he had to be satisfied with third to the M8, Hulme again leading McLaren home, while a torrential rainstorm at Laguna Seca, and a good wet tyre choice, saw John Cannon win in his aged Oldsmobile-powered MIB with Hulme second and McLaren fifth.

Victories for the M8A

Bruce's turn for glory came at Riverside, where he won the Los Angeles Times GP from Donohue, with a bodywork damaged Hulme fifth. Donohue clinched his title at the Stardust GP finale at Vegas, with Bruce nursing his ravaged car home sixth. Throughout the series, only Donohue had posed a consistent challenge through reliability. Both Peter Revson in a Ford powered M6B and Texan Jim Hall in his Chevrolet-engined Chaparral 2G had been able to match the M8A for speed on occasion, albeit without reliability.

For 1969 the M8 design was developed to B specification into what McLaren's Teddy Mayer would later describe as the team's most successful car. The spoiler on the rear bodywork was deleted and replaced by a strut-mounted overhead aerofoil, the front wheel arches were cut back to help exhaust air from beneath the nose, and a short stroke, big bore version of the 1968 engine, now 7046 cc and 630bhp, was prepared by George Bolthoff. Testing again began early with a modified M8A which was converted to full B specification once that had been settled.

In an ill-disguised attempt to give rivals a better chance of getting on terms with McLaren, the Can-Am organisers had stretched the series from six to 11 rounds, but as it was to transpire, the ‘Bruce and Denny Show’ had only been playing in the provinces in 1967 and '68. For 1969 it made it right to Broadway. In an unmatched achievement, McLaren won every one of those 11 rounds. Bruce triumphed in six, Denny five. In eight the 'orange elephants', as the M8Bs became known were first and second. At Michigan Raceway in the eighth race they were first, second and third, Dan Gurney handling the spare car after Jack Brabham had qualified it. A year later in less happy circumstances he would again play a significant role for the team…

M8D

Hulme in his McLaren M8D, 1970

Hulme won this race at Las Vegas in November 1968, driving the M8A
 
While the M8C production version built and marketed by Trojan in Britain was still a season away in 1969, there were various customer M6s and M12s, and Gurney tried unsuccessfully to match his M6B 'McLeagle' on 5.6-litre Ford power against the M8Bs when he wasn't guesting for Colnbrook. Lola, whose T70 had won Surtees the first Can-Am title in 1966, had had a poor 1968 with the T160 and didn't fare much better with its development T162/163 models, while Ferrari, having raced sporadically in 1968, ran Chris Amon in a developed version of the 612 six-litre V12 car at he had driven in the last round the previous year. The former McLaren driver finished third on his debut at Watkins Glen and created a sensation by leading Hulme at the next race at Edmonton before finishing only five seconds in arrears. Thereafter, though, the Italian thoroughbred proved breathless with its litre disadvantage and never again posed a real threat. After it broke its engine at Laguna Seca practice McLaren offered his old employee a ride in the spare M8B but with typical Amon luck its differential broke.

The narrow-track Chaparral 2H for Surtees was a total disaster, proving that even Jim Hall could make mistakes, while Jack Oliver's Peter Bryant-designed Autocoast Ti22 (type numbered after the chemical symbol and valency of the titanium from which it was made) showed late series promise. The car that caused the greatest interest, however, and which would ultimately prove the most significant newcomer from McLaren's point of view, was the 4.5- then 5-litre Porsche 917 Spyder driven by Jo Siffert. He had a few reasonable placings but, like Amon, suffered from a capacity deficit, proving the American adage that there Revson's 8F, at Laguna Seca in 71 is no substitute for cubic inches. Later Porsche would add its own rider to the effect that there was no substitute unless you had a turbocharger…

With the train running smoothly on its rails, McLaren spent the winter perfecting the latest M8 derivative, the M8D. A ban on strut-mounted wings saw the rear bodywork sprout attractive fins between which a low wing was slung, and as the existing tubs were retained, albeit with 4¬inch wider suspension, the wider bodywork curved in neatly where it rested atop the chassis. Bolthoff overstretched himself and the engines by trying an 8-litre 700bhp version in tests, and when this monster exhibited self-destructive traits, 7620cc units were substituted. These developed 670bhp at 6800rpm and a massive 600 lb ft of torque. This was thought to be sufficient.

McLaren's fatal crash

On 2 June 1970, at Goodwood, McLaren was conducting routine testing in Hulme's intended race car when a tail securing pin went missing. Wind pressure ripped away the rear bodywork and wing and, devoid of its downforce, the M8D slid broadside into a marshal's post at well over 100 mph (161 kph). Bruce McLaren, just short of his 33rd birthday, was killed.

As a man he had always had the respect of his fellows and race enthusiasts the world over; as a combination of driver and brilliant engineer/designer he had no equal. Understandably the team took his death very badly, but somehow it kept going, its plight made no better by the severe burns Hulme's hand had sustained when his ride for the Indianapolis 500 caught fire.

'The Bear' was teamed with Dan Gurney when the shattered Colnbrook equipe faced the starter at the first 1970 Can-Am race at Mosport 14 June. Dan took pole but both M8D drivers got a fright from Oliver in the Autocoast; a controversial incident between Oliver and privateer Lothar Motschenbacher in the lapped M8A-based M8B let Gurney get clear to win, but the Ti22 was quick enough to stay ahead of the injured Hulme. Gurney won again at St Jovite while Denny took his turn at the next three venues. By Elkhart Lake in August Gurney had been obliged to quit because of contractual clashes but F5000/F1 McLaren pilot Peter Gethin was drafted into his place and won. At Road Atlanta it finally seemed that McLaren had met some worthy opposition when Vic Elford made his debut in the innovative Jim Hall Chaparral 2J which Jackie Stewart had driven earlier at Watkins Glen. 'Quick Vic' took pole position in the boxy white device which used a small auxiliary engine to suck the air from beneath its skirted chassis to produce ground effect and phenomenal adhesion, much to McLaren's consternation. In the event the 2J broke and both M8Ds crashed, victory falling to Tony Dean's outclassed private Porsche 908.

Thereafter the series was dominated by Hulme, but the paralysing speed of the Chaparral continued to turn cold the marrow of the Colnbrook team's bones. At the Riverside finale it was on pole by two whole seconds, (most runners would have given their eye teeth to pip a McLaren to pole by two tenths) and the protests began to fly. Eventually, to Hall's disgust, the 2J was outlawed. But if that produced a huge sigh of relief at McLaren the future was only partly rosy. After a backflip at St Jovite, Oliver proved an M8D baiter in the Ti22, while Peter Revson had proved quick, especially at Donnybrooke where he ran Hulme close from pole position, in the Lola T220. At least one potential enemy was converted to ally status when Revson was signed to partner Hulme for 1971, but the downside was that Stewart would replace him at Lola, where an all-new bullet-nosed T260 was taking shape.

Development of the M8E

Through 1970 Hulme had actually tested what at the time was dubbed the M8E, which was intended to spearhead the 1971 programme, but that designation eventually went to that year's Trojan customer car and the works car became known as the M8F. This was similar to the D save for full-length fences along the upper bodywork to promote more downforce, and 8.1-litre Chevy engines prepared once again by Knutson. With aluminium cylinder blocks courtesy of sponsor Reynolds, power was again increased to an incredible 740bhp.

Where the M6A had been the design work of Robin Herd, and the M8A that of Swiss engineer Jo Marquart, in collaboration with Bruce, the M8F was the work of McLaren stalwart Gordon Coppuck. This time the changes included a longer wheelbase, inboard rear brakes to reduce unsprung weight and a stiffer chassis. Once again the old cars were sold off to privateers, while sundry new M8Es were sold.

The new season began with a shock, as Stewart planted the Lola on pole at Mosport on 13 June and led prior to gearbox problems. That left Denny to lead Peter home, a pattern repeated at St Jovite and reversed at Road Atlanta and Watkins Glen. However, Stewart continued to be a thorn in the McLaren flank and duly won at Mid-Ohio when both M8Fs broke CV joints. Revson won at Elkhart Lake but Stewart was again quick, as was Oliver who was now in an unreliable Shadow. Revson won twice more, in convincing style at Donnybrooke and under a cloud at Laguna Seca where he ignored the black flag in the closing laps when leaking oil. Denny then endorsed the McLaren domination by taking the remaining races at Edmonton and Riverside, although he couldn't quite amass enough points to hang on to his title, which passed to the deserving Revson. As a sign of the opposition's desperation, sabotage was suspected at Edmonton when a bolt was found in one of the injection trumpets on Revson's car. He was obliged to start late while it was fished out.

Thus ended the season in which the team had faced real opposition on a consistent basis. Ultimately, although Stewart had frequently led, the McLaren proved the better, more reliable car; Lola was handicapped, however, by having only a single car entry.

Peter Revson driving his M8F in 71

The showdown with mighty Porsche

Then came the news that Porsche would mount an all-out challenge for the 1972 Can-Am, and would have its efforts managed by the highly professional Roger Penske for another skilled driver/engineer, Mark Donohue. At last, after so many years of fighting paper tigers, the showdown had arrived. The Can-Am town would ultimately prove big enough for only one of them.

Coppuck's response was an all-new McLaren, the attractive M20. To pack as much weight within the wheelbase for a low polar moment of inertia, he moved the water radiators to the sides, supplemented the usual sill fuel tanks with one behind the seat, and stretched the wheelbase to 100 inches (254cm). Suspension remained much as per M8F but the bodywork was neater and an aerofoil was slung between the two front wings. In testing, the car was quick, and won praise from drivers who appreciated the fact that cockpit heat from front radiators was now a thing of the past.

First blood at Mosport

McLaren's other secret weapon for 1972 was a deal with Jackie Stewart but when he had to pull out due to a stomach ulcer, Revson was asked to combine the Can-Am with his McLaren commitments in USAC.

It was Hulme who drew first blood at Mosport on 11 June, baptising the M20 with a lucky win. Donohue had run into trouble but staged a fine recovery and just failed to pip Denny's sick car. Revson was third. At Road Atlanta, Donohue was replaced by George Follmer after a huge testing shunt and while the American sped to an early debut win, Hulme back flipped at 190 mph (306 kph). He escaped with no real injury, while Revson set a new lap record but retired with no oil pressure. At Watkins Glen it was Follmer's turn for trouble, Hulme heading Revson for an M20 1-2 with Francois Cevert third in Greg Young's ex Revson M8F. Then, for the first time in a long while, the works McLarens were soundly thrashed at Mid-Ohio. Follmer won, Oliver was second in a new Shadow and Milt Minter's Porsche beat Hulme for third. Follmer won again at Elkhart Lake after polewinner Hulme suffered ignition failure. Revson had a dud clutch, but Cevert was second despite a sick engine.

M20 in the pits

Worse was to come, for Donohue was out of hospital for Donnybrooke, ready to back series leader Follmer. A ferocious duel saw the M20s stay with the turbo Porsches until the British cars blew their engines; Donohue then blew a tyre and Follmer ran short of fuel on the last lap. Through it all, like a knight on a charger, came Cevert to win.

ABOVE: Views of another ex- VDS, ex Johnny Jordan McLaren M8E, used in both Can-Am and lnterserie racing. For many years this car held the lap record at Silverstone: 50 seconds dead

The writing on McLaren's wall

That, however, was to be McLaren's 43rd and last Can-Am win. Donohue won at Edmonton after Hulme led for a while, could have done so at Laguna Seca but slowed to let Follmer through to clinch the title, and then had the compliment returned at Riverside only to pick up a puncture, handing George his fifth win. The writing on McLaren's wall said only one thing: get out of town.

The M20s could often match the fast Porsches' practice pace, but come the race reliability lay with the German cars. The M20s either had to run off pace with detuned engines, or risk mighty breakages if they tried to match their rivals' power advantage. Hulme frequently bitched about screwdriver-tuning for extra power, something that would eventually become familiar in the GP world where, ironically, turbocharged McLaren-Porsches would prove so successful.

Private McLarens appeared in the 1973 Can-Am and Europe's Interserie equivalent, but the works cars never raced beyond 1972. In the last Can-Am race of 1974 at Road America, Elkhart Lake, Scooter Patrick had a lucky win in an ex-works car after Jackie Oliver's Shadow blew up. They had had their period of dominance - one of the longest in any professional racing series - and had in turn been dominated. Neither Teddy Mayer nor Phil Kerr of McLaren felt inclined to try matching Porsche's vast budget in the development of turbocharging and as Denny Hulme finished runner up to George Follmer in that 1972 series, the end was finally written to an outstanding chapter in road racing. Thereafter McLaren concentrated on the high-power arena of Formula One.

 

MODEL TIMELINE:

M6A - 1967

 

The first car, M6A-1, was completed and ready for testing at Goodwood on June 19, 1967, more that three months prior to the opening race in the Can-Am series. The car covered over 2000 miles of testing before its debut at Elkhart Lake. Team McLaren won its first Can-Am Series with these cars designed by Bruce, Robin Herd, Don Beresford and Tyler Alexander. It was as simple as possible, consisting of single curvatures and square section tubing wherever they could be used. The M6A was a works car and only three were built.

Chassis: Full monocoque formed from aluminium alloy panelling bonded and riveted to steel bulkheads and carrying two 25-gallon fuel cells in the side pontoons

Suspension: Unequal length upper and lower wishbones, anti-roll bar and coil spring/shock units in front. Upper and lower wishbones with twin radius arms anti-roll bar and coil spring/shock at rear. McLaren cast magnesium wheels, 15 x 8½ inch front and 15 x 13¼ rear

Brakes: Girling ventilated discs front and rear, 12 inch diameter, with 16-3-LA calipers and dual hydraulic circuits

Body: Reinforced polyester resin panelling

Engine: 5.9-litre Chevrolet V8 with Lucas fuel injection and 5-speed Hewland LG transaxle

Dimensions: Wheelbase 93.5 inches, front track 52 inches, rear track 52 inches. width 68 inches, height to top of windscreen 31 inches, weight less fuel 1300 pounds distributed 40 percent front/60 percent rear.

M6B -1968

The M6B was the production version of the championship-winning M6A and differed very little from the original. It was built by Trojan and was offered in a rolling chassis complete waiting only for a motor to be fitted. It was in tremendous demand and a total of fifteen (plus three coupes) were built and their specifications were virtually identical to those of the M6A.

M8A - 1968

 

The 1968 Can-Am works cars were further developments of the very successful M6A design and were again kept as simple as possible, employing single curvature panelling and square tube sections in the monocoque, which now used the engine as a partially stressed structural member. Three cars were built, dominating the series with Denny winning the championship.

Chassis: Aluminium alloy and magnesium panelling monocoque based on steel bulkheads and using the Chevrolet engine as a partially stressed structural member stiffening the rear bay

Suspension: Single top link with radius arm, lower wishbone, anti-roll bar and coil spring/shock units in front. Twin radius arms with single top link, reversed lower wishbone and coil spring units at rear. McLaren cast magnesium wheels 15 x 10 front and 15 x 15 rear

Brakes: Lockheed discs all around, 12 inch diameter with 17/3P calipers and dual aerodynamic surfaces

Body: Reinforced polyester resin panelling

Engine: Chevrolet V-8 with 4 speed Hewland transaxle

Dimensions: Wheelbase 94 inches, front track 57.6 inches, rear track 56 inches.

M8B - 1969

Three new and further developed Group 7 works cars were built for the 1969 Can-Am series, using at least one of the original M8A monocoque. They differed form the earlier cars in body design, using wings that stood high above the tail on suspension-mounted struts and had new 7-litre engines built by George Bolthoff, an ex-Traco engineer. There were minor detail differences between the M8Bs and the M8As. The 1969 cars used larger wheels - 15 x 11 front and 15 x 16 rear. They were unbeaten in the 1969 season and took Bruce to his second championship.

M8C - 1970

Trojan produced this production version of the all conquering M8 series. Modifications were made to accommodate engine choices as stipulated by the customer. Trojan manufactured 15 M8Cs.

M8D - 1970

M8D with Denny driving

Three new cars were built for the 1970 Can-Am Championship and were improvements of the previous model. This model incorporated airfoil sections mounted on fins rising form the rear fenders. These cars earned the nick name of "Batmobile". The M8D ran engines built by Bolthoff and they again were successful in winning the championship. Hulme won the championship after Bruce was killed testing the original M8D at Goodwood.

M8E - 1971

Photo from the family collection

Trojan produced this model as the 1971 production car based on the prototype tested by Hulme. It has the basic shape of the M8B with a lower wing rather than the fins of the M8D. The track is narrower and the bodyshell is smaller.

M8F - 1971

 

The 1971 Can-Am M8F car was designed by G. Coppuck and included a number of innovations. It ran with an 8-litre Chevrolet built by McLaren Engines using the new Reynolds all alloy cylinder block. Horsepower was rated in excess of 740.

Trojan production cars for Can-Am were M8FP models in 1972.

M20 - 1972

 

The M20 Can-Am car was built around the "coke bottle" platform with a low polar movement chassis, with the cars mass concentrated well within the wheelbase.

Chassis:

Suspension:

Brakes:

Body: McLaren fibreglass

Engine: 8.1-litre Chevrolet V8 Fuel injected semi-stressed, steadied on the rear of the tub
Dimensions: Wheelbase 100 inches extended 2 inches from the M8F specifications.

Photos by Don Markle

M6GT

M6GT - 1969

Following the successes of the M6 series in Group 7, a Group 4 GT model was projected for the 69 series. Unfortunately the type met with various problems preventing its homologation in its class and the project was shelved after 4 examples had been completed. The prototype was sold to David Prophet who raced it, later converting it to an open racer. One was completed as a road car for Bruce to test as a prototype for a road car series bearing his name.

 

McLaren M20

The next stage of evolution as practised by Can-Am's Establishment

By Pete Lyons

Although they usually manage to avoid producing camels, the men at the McLaren establishment operate as a committee when designing new cars. They are a conservative group – racing experience produces conservatism and don't seem the least bit sorry not to have a reputation for wild innovation. When they do lay down an all-new racer it's apt to draw heavily on what worked before. So it is with the M20. Most of the pieces are familiar and everything is good, sound, sturdy McLaren practice. Yet it is a much better car and seems to have achieved everything the committee wanted after teething troubles were sorted out.

Gordon Coppuck: "We've taken great pains to get the weight distribution about the same as last year's car, but with a lower polar moment of inertia (isn't that an Eskimo's tea break?) to produce a quicker and more predictable car. We've added two inches to the wheelbase, although there's an 8-in. spacer ahead of the gearbox which moves the engine up more toward the middle of the chassis. The driver has been moved forward as well, while the radiators are back amidship and the fuel is maintained in a more compact mass."

Isn't much of this similar to last year's Lola T260 in layout? "I feel Eric made a mistake on that, doing it like a Formula I car. A slidey, throw-it-around sort of car. Our experience is that a Group 7 driver who throws it around is going to lose it. We prefer to have the car stick right down to the ground."

Tyler Alexander: "The first thing we wanted to fix was a problem we'd had on the earlier cars… I'm not going to say what it was."

"Was it a matter of front-end adhesion?"

“Ah… partly."

Teddy Mayer: “The first reason for the radiators in the sides is to lower the cockpit temperature, but it also allowed us to do more with the aerodynamics at the front, create more aerodynamic efficiency. And we got it, we were about 10mph faster on the straight at Watkins Glen this year – about 192, I think.

"Then we wanted zero change in the weight distribution between full and empty, and we've pretty well achieved that. There are some small geometry changes; the track and wheel¬base are bigger. The car is about 25lb (11kg) lighter than last year's, and it's got a lower polar moment and also the weight distribution is changed; it's a little more toward the front. The roll centers are 'in-the-air'-above ground. There isn't any anti-dive. There is some anti-squat, about the same as last year or maybe a little more. The radiators are something like 25 or 30 percent bigger in area, not because they have to be when you put them on the side but because the M8F's cooling capacity was pretty marginal.

"Gary's improved the engines quite a lot this year – at Mosport our engines weren't good but they are now. There's a little more horsepower and the torque is better, it's flatter, it doesn't drop off so much at high rpm.

Peter Revson's impressions: "It's a better balanced car than the M8F and there's less understeer. Because the balance is better you're able to get out of the turns faster, get the horse¬power down to the ground better coming out of the turns. I can't say I can really feel this 'lower polar moment' subjectively. But the cockpit is cooler, a lot cooler."

Denny Hulme: "We wanted it to run cooler, that was the main thing – and it made all the difference at the Glen this time, I can tell you! And it's a faster, better balanced car. I don't know about the 'low polar moment' business; it's not something you can feel in the seat of your pants. What makes a race car quick is balance. What's happening at one end you want happening at both ends, even-steven. You want balance; else you'll fall off the high wire!

"Basically there's no change in weight distribution between the start and finish. It's very good and it stays fairly neutral. Quite often in the F1 car we've got that problem but not in the Can-Am car now.

"And we've got some mighty brakes. That's mainly due to Lockheed; they've spent time with us getting big, light brakes. At first the pedal wasn't good enough, but it's slowly become better. The brakes are better, especially when you consider the work they do, the energy they have to absorb; it must be enormous, if you calculate it.
"There are some geometry alterations, but I can't really describe what they are – close as I am I don't really take much notice, and an outsider wouldn't have any idea. You never know the effect subjectively of these things, it's just a quicker car or it isn't. Everything we've done has had a slight effect and it all adds up."

So: driver and engine cooling, nimbler handling with more front adhesion, cleaner aerodynamics – all with the same rug¬gedness and reliability that have paid off before. Motor racing to Teddy Mayer is not to dazzle everyone with technology, it's to balance the books and keep faith with your sponsors by winning races. The M20 is a tool to do that job.
What's old and proven about it are the working bits: engine, transaxle, suspension, brakes, wheels. The engines are all big Reynolds aluminum blocks of 509 cu in. (4.5- by 4-in. bore and stroke) with detail improvements, pistons especially, to give about 750bhp and a better, flatter torque curve.

The gearbox is Hewland's strong big Mk II, as it was last year with the exception that it's the USAC version with a starting-motor shaft sticking out the back. This isn't for use with an external starter like Indy; it's because the new seat-back fuel tank prevents. access to the front of the engine when the mechanics want to turn it over. The 8in. spacer casting between engines and gearbox is hollow and does nothing but fill space, while Porsche on the 908/3 and Alfa Romeo have put their gearboxes in that empty space, and March tried it on the nix F1 car. Coppuck says the impossibility of changing gear ratios makes the amid-ships gearbox impractical. The suspension members look as they did before. The geometry changes are due largely to the different arrangement of components, the longer wheelbase and wider track and such details as the chassis being about one inch shallower. The brakes continue trends begun late last season, in that the front discs are larger instead of being equal with the backs.

Late last year Revson's car had cross-drilled discs. but now they have found the same job can be done by machining grooves in the disc faces; typically there are three grooves per face running tangentially out from the hub to the edge. Their function is to prevent both pad dust and pad material "out-gassing" from interfering with friction.
 
The new chassis is bent up out of I6- and I9-gauge aluminum, riveted and bonded to itself as before, but this time the front suspension loads are taken not with a full steel bulkhead but by small steel brackets mounted on the tub. Yet the front of the chassis is designed to be stiffer than before. (There is no front radiator ducting/mounting structure to absorb collisions.) The shape of the tub is largely determined by the new radiator location, as fitting big enough cores takes up all the space right down to the bottom of the chassis. Therefore the outside edge of the fuel tanks had to be cut away at the rear to form a nice (and very carefully drawn) smooth air entry. It is this that produced the F1-style "Coke bottle" shape in plan view. To gain back the lost capacity an 18gal tank was put across the width of the car behind the driver's seat; it is actually the 5th fuel cell in the system, into which the other four (two per side) feed, and this new flow system helps position the several hundred pounds of liquid in the middle of the wheelbase as it burns off in a race.

The new car's body shape looks much like the old and in fact descends directly from it: the technique is to make up one more of the old body in extra heavy cloth, cut it into pieces and drape them over the new chassis, and then fill in the gaps to produce a male buck of the new body. The changes on the M20 are at the sides, where air is induced to flow into the radiators, and at the front where an airfoil rides in the gap between the wheel arches where the radiator ducting used to be – the radiator used to throw its exhaust air upward and produce downforce, but the airfoil does it more efficiently and is adjustable. Both drivers, incidentally, say there is no reduction in the buffeting of their heads from this air flow, but since it's cool air pouring over the top the cockpit, it is much more comfortable. A neat touch about the new nose is that it hinges up for access; furthermore, the struts that mount the hinge are adjustable for length and allow small adjustments in nose-rake angle.

Under the skin probably every piece, familiar or not, has been revised. The "beam," the rear crossmember which carries the top suspension, is much stronger this year and the lower pickup casting is more elaborate to feed the loads into the differential casing more evenly. With stronger U-joints, they measure about 0.75in. wider. Denny is content to have his rear brakes inboard again this year. One of the maintenance improvements is the method of mounting the front of the engine: as before it's hung on a plate running across the chassis but this time the plate is actually three pieces butted together with "fish-plates." When changing engines the "fish-plates" are disassembled and the central portion of the main plate, complete with all three pumps, comes out with the engine. It saves a little time, yes, but the mechanics say a bigger bonus is that the pump installation has all been dyno-tested with the fresh engine, so they know it all works and doesn't leak.

When testing the prototype M20 a great deal of worry went into getting the radiators to work their best. Several different detail configurations of inlet duct had to be tried before the final arrangements evolved, and the same trouble was caused by getting the air out. Also, the first radiators of aluminum had to be replaced with copper ones – apparently copper can be in thinner sheets and you get more flow through a given size core.

Once out in the world there had to be several significant changes. At Mosport the two new cars did not go well at all. Part of it was engines, part of it was tires: Hulme says Mosport proved to him and to Goodyear that the Porsche and the McLaren need different tires, and part of it was indicated by the changes made for Atlanta a month later. There were modifications to spring rates at both ends and the track was widened about 2in. To be specific, both cars had spacers of 0.9 in. put under each front wheel, and Hulme's car had longer links to do the same job at the rear, a job so involved that only his car was done at that time. By Watkins Glen both cars had the new track measurements and it was done at both ends by longer links and wishbones. Brake cooling ducts were let into the front slope of the nose, replacing the original inlets which had been obscured behind the front airfoil in the panel ahead of the footwell. Another change was to reposition the rear airfoil some 6in. more to the rear; this was done at Atlanta on Hulme's car in testing and later transferred to Revson's car to compensate for his not having the wider rear track.

The advantage seems to be to get the wing back in cleaner air so it can work at a lower attack angle. In fact it proved a 2-edged foil; Revson kept it at the Glen and found he was indeed able to pull up on Hulme on the straight, but in the corners when following in the "dead air" behind the leading car, which always robs the front of adhesion, the added leverage of the rear wing created even worse understeer than usual. In practice at Ohio he found its leverage increased the "pitch-back" on acceleration out of the slower corners and generated too much understeer. And he removed it for the race.

Another change to the aerodynamics was in two stages and was once again aimed at taming understeer. At Atlanta both cars had little molded lips, or "shovels," riveted to the front edges of the body to prevent air going down from the stagnation point and around the edge under the car. These remained for the Glen race, and at Ohio the same treatment was applied to the leading edge of the nose airfoil.

Aerodynamics demonstrated its truly awful power on the 5th lap at Atlanta when Hulme's car flipped backwards like a hydroplane gone amok. Apparently it was a nasty combination of circumstances: he was close behind Follmer in the Porsche, which robbed the McLaren of nose adhesion; he had just gone over the crest of the rise in the back straight and he had just hanged into top gear so the nose was pitching up as the clutch gripped. Perhaps, although he doesn't remember anything about it, he was just then darting out of the Porsche's draft and catching a sudden blast of wind. The combination of effects was enough to raise the nose into an angle of attack, giving positive lift rather than negative-several hundred pounds of lift. Ugly, ugly.

Denny has a sturdy New Zealand skull and recovered quickly. Two weeks later with his new car (actually the prototype refurbished to the latest specs) he ran away with the Watkins Glen Can-Am flag-to-flag.

The third and fourth races in this year's series were fascinating demonstrations of what people like about motor racing: You never know what to expect. The turbocharged Porsche should have been a cannon on the Watkins Glen straights, but it bombed. The McLarens, bounding back from their debacle at Atlanta, absolutely ran away one-two. Two weeks later the Porsche should have been a terrific handful on the tortuous Mid-Ohio track, but it started from the pole, blew the McLarens off, lasted on dry tires through a rainstorm which had the one surviving McLaren in the pits five times to change tires, and won very convincingly. Nothing is sure about this sport.

At Watkins Glen Revson was on the pole (the only driver under the magic 100-sec lap time) but from the first turn Denny stormed ahead and went all the way to the checker. Revvie hung on as best he could and actually set the race lap record. He had some idea of passing the old man to win himself a motor race for a change, but a couple of things held him back. His brakes faded away badly – nobody seemed to understand why – and also he had an aerodynamic imbalance whenever he came close up into Hulme's turbulence.

Another super show at the Glen was put up by David Hobbs, who put in a brilliant drive in Steed's Lola and passed everyone but the pair of leaders to hold a solid third, before having to drop back from exhaustion caused by heavy steering and high cockpit temperatures. Francois Cevert took Revson's old M8F ahead to make it McLaren one-two-three. The Shadow had another terrible day, brake trouble holding Jackie Oliver down the field before finally pitching him off into the guardrail and retirement. And the Porsche? Simply put, it was a crock. Evidently the handling was down, perhaps because of tire vibration in conjunction with the lagging characteristics of the throttle response, and apparently the engine was duff. Penske had to use the unfreshened Atlanta motor for Watkins Glen too. In the race several minutes were lost with a problem in the inlet-manifold relief vents, the same thing that caused trouble at Mosport although this time it was simply a broken spring. The Porsche factory had chosen this day to fly over a bunch of European journalists to watch their Panzer crush the Kiwis. It'll be a long time before they do that again.

They should have brought them to Ohio instead. Penske took it very seriously, coming early in the week for solid testing with Mark Donohue going around on crutches to help Follmer sort things out. That it all paid off was shown by the Porsche on the pole, a tenth of a second better than Hulme, and by the first lap when Follmer pulled out fully two seconds. He went on from there, spinning twice in the later rainstorm but recovering without losing anything to score L&M's second dark-horse victory on this track. The McLarens were nowhere, Revson having his transmission fail just before the rain and probably being glad of it when he watched his teammate's struggles.

Denny finally made five pit stops to change back and forth between wet and dry tires; still he got fastest race lap right at the end and later was able to joke: "After the first stop I reckoned we might as well do some tire testing, Goodyear pays you five bucks a mile for it." The man who won himself some overdue honor was Jackie Oliver, who drove on through the rain like a demon without stopping or even spinning, was electrifyingly fast in the wet, even faster than some people with rain tires, at one stage hauled four or five seconds on a lap in on Follmer, and brought the UOP Shadow home second on the same lap with the winner. It was Oliver's first finish this year. Milt Minter was almost as fast as Oliver in the rain and even more spectacular, for he spun off twice, demolishing the speed trap the second time! But he gave Vasek Polak's 9I7-10 another good finish of third.

So in four races it was McLaren two, Porsche two, and the ups-and-downs of both marques have given no convincing idea which is the better car.

Drawing by Werner Buhrer 72

Reprint from Road & Track November 1972

McLaren M8F

The latest and greatest Can-Am car and how Denny Hulme drove it at Mosport.

By Pete Lyons

“Balance," states Professor Hulme, thumbs tucked comfortably in his Nomex suspenders, "the whole theory of race cars is balance. That's all there is to it."

He's just in from practising Mosport laps. His new Can-Am car, in its first weekend at the front lines, has not been behaving well. The official qualifying times show the Scot Stewart is quicker, but now Denny is confident of holding him off in the race. The McLaren's tail had been loose, but now he's put a set of older, inferior tires on the front. Not a sophisticated solution, but it works. Balance.

Out in the sunlit paddock the Kiwis have pushed the long M8F into their roped-off bay and stripped off its bright ochre panels. Its bare metal structure seems a familiar sight. It looks like Lothar Motschenbacher's ex-factory M8D a few bays away, and really it looks like Roger McCaig's brand new M8E across the path. The F is in fact a direct progression of the M8 series that have served so well these three years past. Back in the Colnbrook drawing office, we know from the stimulating new USAC and Formula 1 cars, there are plenty of fresh ideas. There are plans for a new Can-Am car which, if built, will be the M20. But probably the F is going to be enough change for this year.

First, the basic car is longer. Three inches have been added to the middle of the tub and now the wheelbase is 98 in., which should have the effect of shifting a fraction of the weight aft and improving braking stability. But the track, which last year went wider in contravention of long-standing McLaren thinking, is narrower again; 60 in. front, 58.8 rear. The suspension geometries are altered, giving modified camber-change curves at both ends and a bit more anti-squat at the rear. The front upright castings are straight off the Indy car and give slightly different geometry as well as being much more rigid. The weight of the rear brakes has been moved inboard next to the transaxle; the intrusion of the l2-in. discs here has forced replacement of the accustomed reversed A-arms with Surtees-style parallel links, which minimize bump-steer.

The transaxle itself is Hewland's new LG 500 Mk II, distinguishable by its much beefier case and side plates. It follows modifications McLaren made to their own Mk Is last year. The big engines have been giving the hapless internals a bad time; this new case should position them more firmly.

The monocoque's fuel-tank sides are made of 0.062-in. sheet to try to prevent shunt-punctures. This is pretty heavy stuff and permits the rivets to be recessed aircraft style. It looks neat, but any effect on streamlining must be negligible. The driver's footwell has been braced with a new hat section hoop, again with the odd collision (fact of Can-Am life) in mind.

Compared with the M8E customer car, the F has a few things made of more exotic materials, magnesium and titanium, and here and there some pieces may be thinner; but the overall weight cannot be very much less. Empty of all liquids the complete car probably scales close to 1550 lb (704kg).

There are two engine options. Gary Knutson, back after two years at Chaparral, builds up normal aluminum-block Chevies displacing 494 cu in. (the 4.44-in. bore of the 430 block with the 4-in. 454 crank) and fits the injection with staggered intake trumpets.

For Mosport he'd developed a torque curve that bulged up to some 600lb-ft and continued to 700 in a straight line over a 1500-rpm band. Peak horsepower reading was about 740, but with Apollo-booster push like that the actual peak seems academic. The drivers were supposed to hold the revs below 7000, but dyno tests have seen these engines running at 7800.

The other option, not used at Mosport, is "the Reynolds motor" with its Vega-type sleeveless block. Partly because of piston-supply problems McLaren has fixed the bore of this at 4.50 in., and in an effort to make it a free-revving unit has elected to use the 427's 3.75-in. stroke, which gives 480 cu in. The trusty slide rule calculates that with the 4-in. crank, displacement would go out to 512 cu in. It would seem that the 800-bhp Can-Am car is not far away, but whether the current bottom ends could hold it inside for 200 miles is perhaps another thing.

Despite what rulebooks seem to think, the first job of the body is to generate squash. To this end last year's add-on "fences" have been made integral and run the full length of the body. Air shovelled up from the wedge nose is supposed to stay on top of the body, pressing down as it flows past, and on its way out over the stern the wing throws it upward again. Most of the inlets that used to be let into the top of the body have been relocated to interfere as little as possible with this airflow. The rear body line ducks down more sharply than it did last year to give the wing more room to work in. For what it's worth in terms of less drag, the side fins are thinner this year, because they no longer carry the full weight of the wing as they did before Bruce McLaren's crash.

The coolant radiator is still at the front, where the air extracted from it helps generate downforce. A large NACA duct in the left side of the body leads to the doubled-up engine oil coolers; a similar duct in the right flank in early season testing delivered air through three hoses to the rear brakes and the transmission cooler but now merely offers a light breeze to the engine bay. The transaxle cooler is now fed from the only NACA inlet in the top surface, one back under the wing. The rear brake discs have neat little metal fabrications scooping up air from under the engine.

The Goodyear tires are designed especially for Group 7 and don't work well on anything else. They mount on 15-in. wheels at both ends, the front rims being 11 in. wide and the rears 17. The front "footprint" is about 9½ in. wide, the rear about 14¼, The tire pressures will be set at around 18 psi and the surface compound will run about 180 degrees Fahrenheit. A front wheel and tire, with weights and security bolts fitted, will weigh about 28lb (13kg), a rear wheel about 40lb (18kg).

 

Every millimeter of the car has been shaped by very careful, very expensive hands. Even a twin parked alongside is slightly different. Both machines will absorb every possible minute, the most painstaking care, the fullest devotion of the swarm of orange-shirted mechanics. After every day of use the cars are stripped for examination. Every critical part, which means nearly every part, is discarded on a strict time schedule and renewed as are cells in the human body.

When the McLaren is clipped together again, it drapes across its wheels with the loose grace of a relaxed athlete. Every line seems to suggest some vaguely evil purpose. The splayed injector horns, tinted light blue, plume from the glistening deck like outrageous irradiated flowers. Says Hulme:
"Shooting up the straight you're going about 175. Right at the crest of the hill you've got to ease up on the pedal. You mustn't let the nose get too high, or you'll get air under it and you'll take off. You mustn't touch the brakes, either, because you don't want the tail to get light. You just ease over the hump, sort of float. Then once you're down you get all over the brakes, get down to third, for turn eight. It's pretty bumpy through there, the surface is terrible, and I stay over to the inside as I go in. You'll often find me taking a different line to everybody else. Out at Elkhart, especially.
"Once you get into eight the surface is smooth; in fact it's one of the few places here where it is smooth. So you can put a reasonable amount of power on early, and get it all on-or off-and-on-early. You'll find you can put the right front wheel up on the curbing. It doesn't disturb the car. You want to stay over toward the right of the road to be placed properly for nine. You come off the gas smooth and easy and sort of roll around nine to the left. I can't seem to get the car right in against the left curb for some reason, it wants to stay a couple of feet out.
"Then you can give it a bit of a squirt if you want to, and get right over to the left; hard braking, get down to second, and then straight across to the apex of ten and out the other side, keeping straight as the road drops off level. You don't want to give it too much power here, get too far sideways; you could if they'd build up the edge of the road.

I interrupt, saying I suppose another reason not to let the car power slide is that we understand it exaggerates this tire vibration problem everyone's been having.
"Don't seem to have that with these tires we've got fitted today. Can't seem to feel it. But you can go out and tell who has it and who hasn't. You can see it in the marks they lay down coming out of the corners.

"You snatch third past the pits, shoot under the bridge and get set up for one. Don't get too far over to the edge. Touch the brakes. It seems you could take it faster, but there are bumps all down through the first part and they make the car understeer. You mustn't toss the car. You must be smooth, let the car just roll in, or you'll hit the rail like that guy did this morning. It's a bit like Indy, this turn. You think you need to stay right in the groove but you'll find you can get away with leaving it to get around traffic.
"When you get the power on the car goes neutral. You can't actually nail it until you actually get out of the corner. The instant you just crack the throttles you've got forty per­cent of your power. We've got lots more horsepower and torque this year, and it's got just the same holes for the air to go through, and it all happens much more violently."

I say I remember the number of times last year he asked for a 430 because it was smoother to drive.

"Right. In fact it isn't until now I realize just how good the 430 was. Another thing about turn one as I think about it, I just now see why it seems slower this year. At the exit out near the rail the surface is bad. It's always been rough but it's worse now. You can't run on it.
"Up toward two, staying in third – in fact you'll be staying in third all through here until you get to five – you must back off for two at what seems too early. You brake a wee bit and then get right off the brakes and let it roll over the crest. If you let the braking go later and later it disturbs the car too much, because the road drops away from under you. It's like turn seven at Riverside in that respect. Then there's a new bump at the apex, a bloody great patch.
 "I notice Jackie's going wide around it and then pinching in tight later on down the hill. This is one of those places I told you about, where I'm apt to take a different line from anyone else. I run across the patch and then let the car go out wide.
 "I remember with the high wings a couple years ago it was really keen down through there you could really nail it. You'd come out the bottom like a rocket.
"Going up into three is another of those bumpy places, where you've got to be smooth. None of this lock-to-lock business. Coming out it's like the other corners; you can't give too much power until you're really out.
 "Then heading into four I give the brakes a wee bit of a pump to make sure the pressure's up, then steady gas down into the valley, all the way down to the bottom. Then maybe I'll give it a squeeze right at the bottom, then hard on the brakes and straight down into first gear. It doesn't seem to matter where you are on the road here, you can be inside or outside. I flick the car in here and give it a big boot and get it sliding up over the crest and heading for the hairpin."
 
Pete Revson has been leaning into the conversation, and now he interrupts with a puzzled frown. He can't make his F do that. If he tries to get its tail out it gives him warning signals. It wants to bite.

"Yeah," says Denny, "I've been seeing that. We must get that sorted out. Mind, last year Dan was getting through there fabulously, much better than me. He'd come rushing right up to me there. I don't know how he did it. But then he didn't seem to be as good through the next part, the Moss hairpin.
"Here's a funny thing. I can tweak the steering hard over long before I get to the hairpin. I can spin it right over to full lock, and it'll carry straight on for perhaps 20 feet. Then suddenly it digs in and takes me right in to the apex perfectly. Then it's wide-open throttle and we're away. It comes out on a lovely power slide, right out to the edge and back toward the middle, tail out all the way. Then just as it begins to get straight you must lift off a wee bit and let the back wheels get locked in.

"Then it's up through the gears – second, third, fourth and you're rushing up the straight again."

Where is this kind of car different from F1?

"Oh, there's not too much difference really. You use the same line and much the same reference points for braking and so on. This probably brakes a wee bit better, because of the body. In terms of power-to-weight there isn't really that much difference.

"One thing about driving these cars is you don't realize you're going as quickly as you are because of the sound, the low apparent engine speed. An F1 has got ten on it, it's screaming and roaring, and it really feels like you're covering the ground."

I've heard that with Can-Am cars the wake turbulence from a preceding vehicle can be troublesome.

"It's terrible. You want to stay in clear air with these. If you're overtaking a back marker and you come into a turn behind him, if you stay over toward the inside of his line you're fine. But gradually he comes in across you, making his apex, and suddenly you're into his draft. Your car just picks up and moves across the road by yards until you come out the other side. Then it grips again and you're all right, and you can run by. Out at Riverside, especially. You know the bend in the back straight, before you get to nine? You're really flying down there, 190 I suppose, and if you get into the bend behind someone your front end goes completely dead and you carry straight on. There's plenty of roadway there so it's all right, and you can carry on and be well placed to get underneath him going into nine. But you must be very, very sure not to alter the steering by a fraction while you're in his draft, because if you did, if you'd put more lock on, once you came out it'd grip again and you'd really go spinning off.

"It's not just bad in the corners, either. Once last year at Edmonton, you know that long straight past the pits, I got up close behind Motschenbacher, I think it was. Really up close, right on his tail. Suddenly I realized my front wheels were off the ground."

Quickly, so as not to appear to be overly impressed by a wheel standing Can-Am McLaren, I turn to Revvie. What are his impressions of the M8F?

"It's definitely a car for a high-speed track. On slow turns there isn't any down force and the back wants to come out – on mine, anyway. Maybe it's just my driving, maybe I'm just not used to it yet.

"One Group 7 car can be as different from another as it is from a Trans-Am car, you know. It's just a matter of how it's set up. Denny thinks this sudden oversteer thing is because of the engine coming on so strong, but I kind of think it's chassis problems.

"It's a car that is very sensitive to changes in things like ride heights. We've been playing with my ride heights and spring rates all over the map. My front end was wallowing and pitching around so we went to stiffer springs to hold it up. But now it has a tendency to 'speedboat' on the straight.
"Compared with my Lola T220 of last year, the steering is much lighter. I'd say that's the major difference. And this car seems to do a better job of keeping level. It's got more front downforce and the aerodynamics are better balanced."

Suppose that right now Hulme were to start laying down a successor to the M8 series. What areas would he try to improve?

"Well… I suppose possibly we'd be thinking about a suspension system more like the F I car. And we might do some looking into aerodynamics. You see the nose on the Lola that Jackie's driving; well, we've been keeping that in mind for some time, it's just that they've done it before we have. One doesn't know just what is ideal for us. You could start in with an exhaustive aerodynamics program to find out – or you could whoosh-bonk it! Probably get the same results."

"Whoosh-bonk" just about describes the race. Stewart's new Lola, the L&M-supported T260, was taken to Mosport for a private day of testing on Thursday. It proved a valuable advantage for the first day of official qualifying, Friday, for he was fastest at 114.5mph, or I min 17.3sec. This was 0.9 seconds slower than Gurney's 1970 record but enough to hold off Hulme and Revson at I: 18.0 and I: 18.1. The Gulf-Goodyear-Reynolds McLarens were in their first day on the track and the drivers were confident of doing better the next day. But a combination of factors slowed the track by at least two seconds on Saturday and Stewart retained his pole.

Saturday night the Lola's engine was replaced, and there was something wrong with the throttle linkage Sunday morning. Stewart found it still sticking on the pace lap, so prudently he let Hulme beat him into the first turn. He had to watch the McLaren pull out a lead of six seconds in the first nine laps. But a back marker, in one fell swoop across his nose, cost Hulme all his advantage and Stewart sneaked by. As soon as he was behind, Denny noticed oil leaking from the Lola's new Mk II transmission, so he relaxed and sat comfortably in second place waiting for the inevitable. It happened just before one-quarter distance and Jackie pulled off course into a stone quarry. As he walked back to the pits he watched Hulme and Revson run easily to another nose-to-tail Orange Elephant win, just the kind of sight everyone had hoped Stewart could prevent.

Reprint from Road & Track November 1971

 

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