The World's Fastest Sports Car
Bruce McLaren has his sights set on the ‘69 Can-Am series and the accompanying American dollar. His quest for the ultimate sports car has resulted in the new M8A monocoque.
After winning the 1967 Can-Am series in his all-conquering M6A Chevy-powered sports car, Bruce McLaren went back to his factory at Colnbrook, near London Airport, and set about designing a car that was even quicker. Why? Because in the race at Riverside Jim Hall’s Chaparral had proved to be closely competitive, and McLaren knew he would have to have a better car for 1968. The M8A (the Formula 1 car was the M7A) weighs around 1440lb (645kg), which is 25lb (11kg) lighter than the ‘67 car, but the aluminium 7-litre dry-sump Chevy V8 engines, modified in McLaren’s own Californian engine division, give around 650bhp - nearly 100bhp more than he won races with last season!
Suspension and general styling are obviously similar to the previous car, although the body shape has been smoothed out a lot, and the general ‘negative lift’ lines of the new body means that the currently popular ‘wing’ isn’t really necessary. The smoother lines also mean that this year’s car can run with lower spoilers on the tail. Since tyre profiles are lower than previously the overall lines are lower with the wheel arches less pronounced.
Slots cut in the back of the front wings relieve the high-pressure area directly over the front guards. NASA-type triangular ducts with a lip at the top feed air into side-mounted engine oil-coolers. These ducts are actually built into the doors on either side, and the coolers are mounted level with the engine mounting plate. A separate oil cooler for the gearbox is mounted in the swept-up lip of the tail as it was on the 1967 car.
A larger air-intake slot in the nose feeds air to a wide radiator, and careful interior sculpting has been carried out inside the nose to make sure that the air rushing through the radiator has been put to maximum benefit by being channelled properly upward, thereby creating more down thrust on the front wheels.
The body comes in four pieces - the nose with fitted air ducts, tail section and two doors which also carry the side-screens. The screen has been specially designed to mould up around the driver - almost like a single-seaer - and it is now impossible to carry a passenger, even though the passenger’s seat is regulation width. The second seat is now almost covered by this perspex ‘tonneau cover’. McLaren isn’t sure whether this is according to Hoyle, but he reckons to try it out anyway.....
The chassis is monocoque, but unlike the M7A with its four fabricated steel bulkheads, the M8A has only two bulkheads. The forward one is set behind the front suspension, with the steering box mounted on it, making for the shortest-ever steering column. The bulkhead is so far back that a special hole has been cut in it to take the full travel of the clutch and brake pedals.
The broad monocoque is aluminium sheet on the inside and magnesium on the outside, with rubber bag tanks carrying 30 gal of fuel on each side of the chassis. The ‘67 car carried only 45 gals, but this was ample for the thirst of the 6-litre cast iron Chevy V8.
The M8A is powered by a special aluminium 7-litre Chevy V8. "Don’t ask us where we got it from," says McLaren with a grin, "which should produce around 650bhp". The interesting thing about its installation is that, like the Ford Formula 1 engines, it is a stressed part of the car’s chassis. The forward face of the engine bolts to a sheet of magnesium, and A-frames running back from the rear of the chassis (it stops abruptly behind the cockpit) bolt to the rear of the engine. A fabricated sub-frame mounts over the bellhousing and carries the rear suspension, while long radius arms run from the rear up rights forward to the back of the monocoque. Although the monocoque appears to extend back past the cockpit, this extra ‘shelf’ on either side houses the oil tank for the dry-sump set-up, and the various pumps and electrical impedimenta to keep the engine sparkling. In fact, the magneto is mounted vertically behind the injection manifolding on top of the engine vee, and the metering unit for the fuel injection pokes back horizontally from the back of the engine.
The high stacks of the McLaren-modified fuel injection are quite fantastic. They look like a bunch of eight shot-blasted stainless steel lilies curving a full 12 in. above the engine – flower power in a big way. The exhausts run into a pair of big-bore stove-pipes that run out on either side of the gearbox below the body. On the M7A the exhausts curled up over the drive shafts, and exited through the tail bodywork.
The Hewland LG500 gearbox has specially tailored internals for the McLarens. Instead of the normal five cogs, this new box has only four special gears (and reverse) with a high bottom speeder’s control. A sump-puller first gear is not needed since all the Can-Am starts are rolling ones behind a pace car.
The new McLaren wheels are the ultimate in fatties. They get more like buckets with every new model! As tested at Goodwood, the M8A had rear wheels 15 in, in diameter and 15 in. across the rim. A sort of round square, if you know what I mean! And they plan to take a set of 16 in. rims with them as well. Front rims are 9 x 15.
To cope with the increasing number of punctures in racing, the new wheels are knock-ons in place of the normal bolt-on wheels. A specially made bar has been made up to undo the single large locking nut. The Goodyear rears measure 14½ in. across the tread. The stopping department is very effectively catered for with a set of the biggest disc brakes and callipers you’ve ever seen. Made by Lockheed (who also makes brakes for McLaren’s Formula 1 cars) the big ventilated discs measure 11½ in. across on the rears, and 11 in. on the fronts. The discs are 1 1/16 in. thick.
Testing on the cars was delayed when McLaren spun his car into a bank in the wet at Goodwood. The programme soon caught up with itself and Hulme and McLaren began attacking their testing records at Goodwood and Silverstone before the cars were shipped to America for the first of the Can-Am races.
Article first published World's Fastest Sports Cars No 8
Bruce McLaren and his team mate Denny Hulme set a unique pattern in 1967 when they finished first and second in the dollar rich Canadian-American series for Group 7 sports cars. They alone of the European constructors realised the prestige to be gained from winning the series as well as the not inconsiderable prize money and the orders for replica cars for the next year’s series. In fact so large was the order book at the end of the 1967 series that the small Bruce McLaren Motor Racing factory near Slough could not cope and they were glad of their tie-up with the Lambretta Trojan people who had previously built Elva sports/racing car under licence. Under the licensing agreement Trojan were to build the production versions of the McLaren, leaving the McLaren factory free to build the works cars and prototypes. Thus the 1967 factory car the M6A became the production M6B and the 1968 factory car the M8A became the M12; the inconsistency in type numbers is explained by the fact that the works decided to call the 1969 factory car the M8B because it was changed very little in basic design.
The formula for this Can-Am series is pretty simple; virtually any size of engine is allowed and you can fit it to any two-seater racing car. Since very powerful pushrod ohv engines are available in America most teams used these, although Ferrari belatedly entered a 6.2 litre four overhead camshaft V12 which showed promise. In 1968 General Motors, who are allegedly against racing, produced a special batch of all aluminium 7-litre pushrod Chevrolet engines which were sold to Can-Am contestants at a fairly low price. The leading teams all used these and the rival Ford engine hardly got a look-in. The McLaren engine men went over the engines with a fine tooth comb and found a few more horsepower as well as converting them to fuel injection and they ended up with something like 620bhp which gave these exciting sports cars a top speed of over 200mph on the fastest circuits.
The basis of the M8A is a very stiff but light monocoque chassis built from aluminium with steel bulkheads which finishes just behind the cockpit, with the engine acting as a stressed member being bolted directly to the rear of the cockpit with the rear suspension mounted on the gearbox. This saves a great deal of weight which is all important in any type of racing. The side boxes of the monocoque tub carry the rubber fuel bags which hold a total of 52 gallons of fuel - very necessary at under 6mpg!
The front suspension is by double wishbones with outboard mounted coil spring/damper units while at the rear the usual single transverse top links, lower reversed wishbones, and radius arms are fitted, the radius arms being the only connection the rear suspension has with the chassis as these are mounted at the forward end of the rear of the monocoque. The brakes are Lockheed 12in ventilated discs outboard mounted all round with plenty of cool air ducting. Steering is by rack and pinion, and wheels are McLaren castings of 15in diameter with 10in rims at the front and 15in at the rear.
The 7-litre aluminium engine supplied by Chevrolet is among the most powerful racing anywhere today even though it uses ordinary pushrod overhead valves. Converted by McLaren to use Lucas petrol injection the engine gives no less than 620bhp at 7,000rpm from its 7 litres (427 cu.in.) and is very light as well. It transmits its power through a Borg and Beck tripe-plate clutch to a very strong Hewland LG 50- 4-speed gearbox.
Article first published 1968-70 Prototype