The McLaren MP4/6 represents the third generation of cars born from the competitive MP4/4. The car, designed by Steve Nichols, under the careful guidance of Neil Oatley, is driven by reigning World Champion Ayrton Senna and Austrian teammate Gerhard Berger, taking part in the 1991 Formula 1 World Championship, with the presentation that takes place just a few days before the start of the season, and adopts the introduction of the new twelve-cylinder Honda engine to replace the V10 used in the previous two seasons.
The Japanese technicians believe the V12 architecture to be superior in performance compared to the previous V10, as it is capable of running at lower revs for the same power output, despite the complexity of the larger dimensions and the additional weight resulting from two additional cylinders.
A unit completely from scratch is then designed, consisting of twelve 720 horsepower V-cylinders, with an angle between the banks of 60°, very balanced given the absence of the balancing shafts that had instead characterized the previous ten cylinders.
As regards the distribution, a cascade system of gears was chosen, given that the synchronous belt system had not given the desired results, which allows to obtain a maximum rotation speed of 15.000 revolutions per minute, with the return of the valves in titanium alloy operated by steel springs without pneumatic return.
In the experimentation phase, the new engine has a bore/stroke ratio of 1.54, which is very similar to the old V10, but reaches the maximum power at a speed of about 800 rpm less than the old unit.
However, the engine is still less powerful than the Renault ten-cylinder, since the latter does not suffer from the resonance phenomena of the springs, since these are managed with the pneumatic return.
To remedy this lack, Honda increases the aforementioned ratio to 1.74, also introducing a system of variable-length intake manifolds to improve the torque curve and the quality of delivery.
Furthermore, the use of Shell High Energy fuels proves to be a double-edged sword for the Woking racing department, which on the one hand guarantees an increase in performance of power more than the Williams of about ninety horsepower, but on the other cause to the unit of the Japanese company of the big problems of lubrication, given by the excessive phenomenon of the centrifugation of the engine oil in the case of high values of lateral accelerations causing frequent failures of the bearings due to the fact that these were not properly lubricated.
To compensate for this lack, McLaren decides to run with an excess of oil and with a very complex recirculation system, generating evident and frequent bluish smokes during the first races of 1991, a symptom of engine oil residues which, during the season, are drastically reduced with the improvement of this system.
The RA121E, as defined by the Japanese manufacturer, remains decidedly unreliable also due to the modifications carried out on fuels with density and viscosity values different from those used at the beginning of the season, requiring a further calibration of the flow meters on the new cars, which, however, is not carried out.
However, this deceives the on-board computer, which reports more fuel in the tanks than there was in reality and, for this reason, in several races both Senna and Berger run out of fuel during the course of the race.
The unit as a whole is longer, heavier, and requires more fuel than the V10, but technicians from the Land of the Rising Sun believe that the estimated power of 720 horsepower at 13.500 rpm would have compensated for these shortcomings.
Despite the power, Senna does not put faith in the new engine, but the Japanese stick to their plans, with the McLaren season starting in the best possible way with four wins in a row, accompanied by the six-speed manual gearbox, unlike Ferrari. and Williams who now have a semi-automatic gearbox, which compensates for the weight increase of the engine.
Regarding the aerodynamics and the chassis, despite the fact that the starting point is the excellent MP4/5B, the car is different in terms of aerodynamic profile, now much more efficient, as the designer Neil Oatley and his team receive a precious contribution from Henri Durand, newly acquired by Ferrari in mid-1990.
Although the car has been aerodynamically improved, the nose of the car remains low, unlike other cars such as the Benetton B191 or the Tyrrell 020, which feature the first experiments with a raised nose and gull-wing ailerons.
Numerous changes must necessarily be made to the chassis, both to accommodate the longer engine and to the enlarged fuel cell. Furthermore, with the four centimeters added to the length of the car, the new tank is decidedly more rigid in terms of torsional rigidity, and consists of an even smaller number of basic components, while a system is used at the front for the suspension. active push rod mounted right in front of the cockpit, instead of being traditionally placed vertically on the sides of the wheels.
Overall, the car turns out to be extremely balanced and with noteworthy grip, and in addition it allows for exceptional tire and temperature management.
Development over the season
Over the course of the season, Honda prepares three specifications of the twelve-cylinder engine: the first version is used at the beginning of the season, leading McLaren to triumph in Phoenix, Interlagos, while the second specification is brought to the Principality of Monaco, which offers better power mid-range thanks to its new induction system.
However, the friction problems are solved only at Silverstone, on the occasion of which Honda brings the third specification of the season, which includes lighter cylinder heads and camshafts for greater power at intermediate speeds.
In addition, in an effort to reduce body roll, new linked rockers are also used and a ride height adjustable from the cockpit is also added. A semi-automatic transmission is tested during the season, and is then converted back to manual, as it is considered ready to be used in a race.
At the beginning of 1992, the Woking team presented an updated version of the MP4/6, with which Senna won a third place in South Africa, before being replaced with the official car of 1992, the MP4/7A, although three MP4/6Bs will be brought to Sao Paulo, on the occasion of the Brazilian Grand Prix, as spare parts.
The season is inaugurated by Senna, who wins the first four races in the United States, Brazil, San Marino and Monaco, before Williams and Nigel Mansell find competitiveness with the FW14.
Constantly reaching podium positions throughout the year helps McLaren, but Senna insists Honda step up the engine development program, requiring further improvements to the car before it was too late. Therefore, Honda provides several upgraded versions of the V12 engine, while Oatley redesigns various features of the car, most notably the side panels and wings.
In Canada, the Brazilian driver was forced to retire, subsequently winning two podiums in Mexico and France, while in the second half of the season he returned to victory on three occasions, in the Hungarian and Belgian Grand Prix, and in the final race in Australia, also winning three second places in Italy, Portugal and Japan.
If in the first part of the season McLaren dominates the rankings, in the second part the English team and the Brazilian driver have to deal with the Williams FW14 and the English Lion Nigel Mansell, who in fact become the team to beat.
The coldness shown by Ayrton earned him the conquest of the world title again, after the English driver ends up in the sand outside Turn 1 at Suzuka, while chasing the now less competitive MP4/6 of the Brazilian champion.
As for Berger, however, his season is characterized by multiple retirements, mainly due to the fuel consumption problems of the Honda twelve-cylinder, winning a victory in Japan, three second places in San Marino, Great Britain and Belgium, and two thirds places in Brazil and Australia.
Senna won the title with 72 total points, leading the English driver of Williams by 24 points, and the 43 points won by his teammate allow McLaren to conquer the third consecutive constructors' title, with a total of 139 world championship points.
In 1992 McLaren brings a version B of MP4/6, as the new MP4/7A is not ready yet. The Brazilian took only a third place in South Africa, before relegating the MP4/6B to a reserve car.
The McLaren MP4/6 closes its history with a total of eight wins, eleven podiums, ten pole positions, five fastest laps, and both drivers and constructors' world titles in the 1991 season, also representing the last car with manual transmission and engine V12 to win at least one of the two world titles.