Mazda 787B

Mazda employed a clever fuel economy plan to overcome Le Mans disappointment and be the first Japanese manufacturer to win at La Sarthe
By Keith Howard

As the 1980s drew to a close, a betting man would have laid money on either Toyota or Nissan being the first Japanese car maker to win at Le Mans. Mazda was in the frame too, but a second-string player. When it tried to up its game for 1990, things went badly wrong – the two new 787s retired early – giving no hint that it might upset the status quo.

But at Mazda HQ there was a determination to turn things around, and 1991 would be the ideal year to do it. A rule change had effectively excluded Nissan and Toyota from that year’s race, while tighter fuel restrictions would hamper the heavier, more powerful Mercedes and Jaguars.

To seize the opportunity and make good its 1990 disappointment, Mazda didn’t just improve the 787 – enhancing both its quad-rotor Wankel engine and its chassis to produce the 787B – it also restructured its racing organisation and formulated a clear, audacious plan to win. A plan based on optimising lap time with the minimum use of fuel; a plan that would require its star drivers to unlearn ingrained habits and embrace a new driving style.

On race weekend it all came gloriously right. The Mercedes were faster but broke; the Jaguars could have been faster but had to rein back to conserve fuel. And so the 787B driven by Johnny Herbert, Volker Weidler and Bertrand Gachot took the chequered flag for a historic double: first Japanese car to win the race, and first non-piston-engined car to do so too.

Through an interpreter, I spoke to Nobuhiro Yamamoto, a chassis engineer on the 787B, about an event that still gives the Mazda Motor Company a warm glow.

Laying plans

“We learnt a lot from the 1990 setback. We reviewed the 787’s performance and found that it had the potential to run only 352 laps in 24 hours, equivalent to the third position Porsche. After this study we set the targets for ’91, including forecasts of the improvements that would be made by other teams. Our target was to complete 357 laps in 23 hours. Our target lap time was seven seconds quicker.

“We worked closely with Nigel Stroud’s design team to develop the car for 1991. In our discussions we found that we hadn’t made any mistakes in the directions we’d taken with engine and chassis developments. What we needed to do was overcome our shortfalls. We identified six challenges. First was reliability. Second, improved fuel economy. Third, the car should be adapted to the track and be particularly effective in the middle speed range. Fourth, we needed to improve the acceleration and cornering performance. Fifth, driver comfort was important. Sixth, we needed to improve the team’s information and communication systems. We worked on all these six areas to develop the 787B.”

Engine and economy

“I had mixed feelings when in 1989 Yasuo Tatsutomi [Mazda’s chief of product planning and development] demanded a 100bhp power improvement. We began using the four-rotor engine in 1988 in the 767 and at that time its power was 600bhp. In the next year’s 767B the power was increased to 630bhp. So we had produced only 30 extra horsepower in one season, with everyone working very hard to achieve it. Now we had to improve by 100bhp! Actually we didn’t achieve that but we did reach 700bhp and fitted a variable induction system which delivered 95 per cent of maximum torque from 6000 to 9000rpm. That represented significant progress.

“An overall 10-15 per cent fuel economy improvement was another requirement but this could not be achieved by engine changes alone. We did improve the engine’s fuel economy but we also ran many simulations to find out how best to run the car in the race and how best to set it up.

“For better fuel economy we needed faster combustion speed and higher combustion efficiency. The main improvements came from relocating the plugs. The conventional rotary engine at that time had two plugs per chamber; we increased this to three, and reduced the plug diameter from 14mm to 10mm.

“Our engineers established the best way of running the car for improved fuel economy. They determined that in low speed corners the car needed to be driven smoothly without pressing the accelerator too hard. We thought this advice might offend the drivers so we hired Jacky Ickx as a consultant. He understood our strategy and persuaded the drivers to follow it. But the greatest contributor was the fuel economy index we displayed in the cockpit, which was also transmitted back to the pits. The drivers turned their thinking upside down and made fuel economy their priority. Our target was 1.85km per litre and they competed with each other to achieve the fastest lap time within this target. Gachot and Herbert learned a lot from Weidler in this respect because he had a lot of experience with racing the rotary engine. We were surprised how quickly they adapted.”

Carbon's contribution

“The switch to carbon brakes was one of the most significant changes in the 787B. Chicanes were added to Le Mans’ 6km Mulsanne straight so braking performance became very important. And with carbon brakes we saved weight and improved acceleration performance.

“We worked closely with the manufacturers to control the brake temperatures and limit wear, and in the end achieved half the wear rate we’d had with cast iron brakes. Temperature control is very important with carbon brakes so we increased the rear wheel size from 17 to 18 inches to make extra space around the rotor and calliper for cooling. In the race we changed the rear pads only once and the rear disc was not changed at all. At the front the rotor was changed once and the pads three times. This saved us pit time compared to 1990. Another example of how we planned meticulously for the victory.”