In developing and producing the MG Metro 6R4 rally car, Austin Rover are continuing a great MG tradition. Many times in the illustrious history of MG, the factory has produced highly specialised cars aimed at sporting achievement. Fabled machines like the all-independent “R”-type racer, the K3 Magnette and the series of record breakers culminating in the EX181, which topped 254 mph with a supercharged 1.5 litre twin cam engine.Now comes the MG 6R4 (6 cylinder, Rally, 4wheel drive) – the most exiting and significant purebred MG competition car ever.Designed without compromise to win rallies – and in particular World Championship rallies, the Group B Metro is providing a golden opportunity for serious rally competitors to build a moderately priced but highly competitive British car. Conceived from first principles to suit the arduous demands of top flight international rallying, the 6R4 has been logically and intelligently planned.Top design talents, advanced technology and a dedicated development team have come together to create a formidable but nevertheless “user friendly” machine.
This brochure sets out the basic facts about 6R4, although it must be stressed that the familiar phrase “our policy is one of continuous improvement” has particularly keen relevance in the case of 6R4.Austin Rover Motorsport under the direction of John Davenport carried out a rigorous analysis of developments in International Rallying before building the 6R4 project into their long term planning.
Fast increasing sophistication in Group B suggested that a quantum leap in design philosophy would have to be made in order to be fully competitive at the point of homologation. At the same time, there were no spectacular budgets or manpower resources available to do this.Just as in its new road car product programme, Austin Rover had to apply ingenuity and original thinking to the design solutions, using brain rather than brawn. It was also implicit in the programme that the 6R4 should provide moderately priced basis for a competitive rally car, in contrast to some of the rival vehicles that require substantial modification and investment to be transformed from the “off the shelf” to a competitive state. What began to evolve was a very special Metro, totally dedicated to the objective of winning rallies.
GRAND PRIX TECHNOLOGY
Building on established links with the Williams Grand Prix Engineering team. Austin Rover Motorsport worked with top F1 designer, Patrick Head and his team, to create the basic structure and layout of 6R4.Taking the usefully compact package of the Metro as a starting point, an immensely stiff and rugged bodyshell was created. Strength is vital for a rally car, which must absorb terrific punishment, also advanced suspension work better when based on rigid structure. Tests have shown that 6R4 has one of the highest torsional stiffness figures for a car of this type. Built in roll cage tubes contribute to this strength. After consideration of several alternative engine location and transmission permutations the 6R4 was given a mid engine, four wheel drive format, providing high levels of traction to match the planned power and torque characteristics of the power unit. These characteristics stemmed from another fundamental factor in the design, the decision to use a large capacity, naturally aspirated engine. This gives the benefit of superior throttle response consistent torque characteristics and mechanical simplicity. Following this line of reason it was also decided to take the unique step in developing a new engine specifically for rallying with carefully tailored characteristics.Yet a further break with group B convention was the logical idea of developing a prototype design through testing and actual competition before establishing the homologation specification. The approach ensured that the definitive vehicle would be far more proven and competitive than would otherwise be possible.
Thus it was in February 1984 that the first prototypes were shown to the world, generating tremendous interest in what was quickly seen as a potential world-beater from Britain. For the development year while the new engine was being prepared a slave V6 unit based on the well-known Rover V8 was used.This interim engine developing up to 250bhp was sufficiently powerful to provide overall vehicle development data and experience. While laboratory and track testing continued apace, the opportunity was taken to enter the 6R4 into a series of UK rallies.It is never possible to fully simulate the rigours of competition under proving conditions; hence genuine rallying was seen as an essential part of the programme. This was a courageous move, when such forays carry the risk of highly conspicuous component failure – all rally teams are acutely aware that a car can work perfectly under testing and then malfunction under the unique pressures of the real event. It was this “Murphy’s Law” effect, which Austin Rover Motorsport sought to exorcise via extensive competition mileage, dovetailed with thousands of test miles in the UK and Europe.
YORK RALLY DEBUT
First public outing for the prototype 6R4, running in the Company’s classic red and white livery was in the 1984 York Rally when the car easily set fastest times in the first eight stages before an overheating alternator cried enough. In other rallies in 1984, the car demonstrated its potential with field-lending stage times interspersed with the very development problems which this activity was intended to seek out. Just as importantly, chassis and aerodynamic developments were accelerated by rally experience – hence the increased wheelbase and track of the definitive 6R4, and it’s prominent down-force generating wings.
Right from the beginning of the 6R4 project the importance of aerodynamic aids has been recognised, and competition experience has proved the stability and control benefits that can flow from careful wind tunnel research.
During the prototype year, Austin Rover gained some very useful extra testing mileage from participation in a television drama series! The programme, screened nationally from September 1985, is the “The Winning Streak”, from Yorkshire Television. It features a 6R4 in a story about a motor trader who goes rallying and includes footage shot on real rallies as well as a great deal of specially staged film.
Ending on a high note, the development year’s efforts were rewarded in March 1985 with a resounding win in the Gwynedd Rally – nearly two minutes ahead of an Audi Quattro A2, despite an off-song engine.
The stage (and the stages) was set for the reveal of the full house homologation car, with its superb V6, 4 valves per cylinder (hence V64V) engine.
The following extract is from the ORIGINAL 6R4 sales brochure!
“The car is very easy to drive – and very fast at only eight-tenths. You would not need to be a top class driver to win with it”. So says Tony Pond, very much a top class driver and a brilliant development driver, who has played a major part in achieving the superb driveability of 6R4.
Based on one of the world’s most efficient cars, the 6r4 is one of the most compact Group B cars available. In any given situation, therefore you have more roads available, more freedom of line. (In practical terms too, more room in the workshop, on the trailer or in the service areas).
Ingeniously laid out for maximum durability, the four-wheel drive transmission features a purpose designed five speed gearbox (synchromesh on the Clubman carts, dog engagement on International boxes) mounted forward of the engine and its twin plate clutch. A step off gear unit takes drive from the gearbox to the central Ferguson-Formula viscous coupling epicyclical differential, which in standard form is set to give a 35/65-front/rear-torque split. Changes to the overall final drive ratio are readily achieved by substituting alternative step off assemblies, which are self contained with their own oil reservoirs.A high duty rear limited slip differential is integral with the engine sump casting, but with separate oil supply. A short jackshaft carries the drive through the sump to the nearside rear drive shaft, while the entire power unit is offset slightly to give equal length drive shafts. A quill shaft connects the central and rear differential to facilitate changes of the entire central transmission unit. Drive to the specially developed front limited slip differential is via a conventional propeller shaft.
SUSPENSION & STEERING
Front and rear suspension is by coaxial coil springs and struts, with rose jointed wishbone hub location. The rear wishbones are reversed, lateral location being by adjustable trailing links. For ease of one-event servicing, a four bolt clamping arrangement is used to connect the strut castings to the hub carriers, a system that has been thoroughly proven on the successful Group A rally and race Rover Vitesses.Fully adjustable upper mounts for all four struts allow castor and camber variations.Intensive development work in conjunction with Bilstein has led to exceptionally efficient damping performance from t eh gas filled struts, even under high ambient conditions.A competition style, centre point take off rack and pinion steering system provides accurate and precise control with minimum bump steer effects.
WHEELS, TYRES & BRAKES
One of the more fundamental changes made to 6R4 as a result of the prototype experience was the adoption of 16″ or 390mm diameter wheels, to allow the use of Michelins most advanced tyre technology.
This has allowed brake disc diameter to be raised from the already generous 10″ to 12″, hence ensuring that braking performance is as remarkable as the acceleration capability
Believed to be the first engine ever designed for specifically for rally use, the Austin Rover V64V power unit is compact, light and very potent – yet has the low speed torque to pull from 1500rpm in fifth gear.
Fully recognizing the unique demands of rallying, with its high speed travel over frequently unknown roads and forest tracks, violent fluctuations in speed and equally violent manouvres, the V64V provides instant throttle responses, massive torque throughout its operating range and the advantage of substantial overrun engine braking because of its high compression ratio. Turbochargers, small capacity engines, do not match these attributes and have the further disadvantage of mechanical complexity and temperature sensitivity.
ANATOMY OF A POWERHOUSE
Constructed largely in aluminum alloy for lightness (the fully dressed unit tips the scales at 143kg/314Ib. The 90deg V6 3 litre engine has an oversquare, bore/stroke of 1:1.22 and a compression ratio of 12:1. Twin overhead camshafts per bank are driven by toothed belts and operate the four valves per cylinder via inverted bucket tappets.
In “Clubman” form as fitted to the homologation cars, the engine is lightly stressed. It has a single throttle butterfly intake system, multi-point fuel injection, relatively mild camshafts and an electronic rev-limiter set at 7000rpm, where the power output is around 250bhp. Maximum torque (225Ibft) is reached at 5000rpm, but the broad, flat torque curve is well above 200Ibft from 3000 rpm to 7000 rpm, giving unhesitating response under all conditions. This engine works for the driver, helping him out of difficult situations and enabling him to give of his best.Even in “International” form, with a power output of between 380-410bhp, according to set up, the V64V engine retains this tremendous flexibility; maximum torque goes up around 27 Ibft and the torque curve stays above 230Ibft in its key operating range 5000-9000rpm.The parts specified to uprate a Clubman unit to full International specification include a six throttle butterfly intake manifold, “hotter” camshafts, high duty connecting rods and appropriate ancillary item’s such as revised engine management electronics.With the International unit, variations such as alternative fuel injector locations, can be affected to further tailor the engine characteristics to different even conditions.
CUSTOM DESIGNED ENGINE MANAGEMENT
Both versions of the V64V engine have the benefit of a specially developed Lucas Micos engine management system.This controls both the sequential fuel injection and the ignition timing, which are mapped against the engine speed and load. Secondary input signals of barometric pressure and intake air temperature adjust for air density changes, while temperature sensors for engine coolant and fuel flow allow the necessary compensations for easy startling at any temperature. Should any of the secondary sensors malfunction, or be damaged, the Micos system is programmed to operate on a “fail safe” average input.In order to optimise engine performance, the injection timing can be varied in discrete steps.