Honda NR 500 GP

When Honda returned to GP racing after a 12-year absence in 1979, they did so with astonishing new four-stroke technology to challenge the reigning two-strokes: The remarkable V-4 oval-piston NR500.
There were many versions of the NR, each pioneering technology still in vogue today.
The NR stands for New Racing, and the New Racing division was exactly that: the NR team was made up of all young engineers guided by the father of the six-cylinder CBX and fabled RC166, Soichiro Irimajiri, and project leader Takeo Fukui who later become director of R&D and President of HRC.

The NR was essentially a V-8 with each set of adjacent cylinders fused together. Each oval cylinder housed eight valves that doubled the valve area possible in a conventional V-4. The oval piston measured 93.4mm x 41mm, and was held by two connecting rods moving through a super-short 36mm stroke. This allowed the NR to reach engine speeds of 19,500 rpm—twice the speed of the two-strokes—and produce horsepower comparable with the 500GP two-strokes.
Honda mythology tells of Irimajiri's epiphany of the oval piston while observing an oval traffic light on his way to work.

Concepts developed in the NR echo prophetically in race technology today: side-mounted radiators, still common to V-4s today, back-torque limiters; magnesium engine bits; carbon fiber componentry including skeletal frame, carbon wheels, swingarm, fork tubes, and brakes.
The second-generation NR500, the 0x model, featured a Monocoque aluminum frame in which the fairing is an integral part of the chassis.

The Oval Piston: Heart of a New and Different Breed

To design a 4-stroke, 4-cylinder engine in the conventional manner would not produce a machine that could out perform its 2-stroke rivals. No, for a 4-stroke engine to generate the same level of output as a 2-stroke engine it had to have twice as many cylinders as its competitor. Moreover, 20,000 r.p.m. was the absolute minimum a 4-stroke engine required to produce superior horsepower.

Increased power meant that the 4-stroke engine would have to consume and exhaust more of the critical fuel-air mixture. In other words, the aperture of the valve would have to increase for enhanced intake and exhaust efficiencies. To do that, the number of valves would increase, also. However, conventional circular pistons would accommodate only four or five valves. Furthermore, such a structure would provide no technical advancements, as compared to the time when Honda was competing in the World GP with its 4-valve DOHC engines. Therefore, the NR project's new challenge was to achieve "innovative technology," being more than a mere refinement of the previous technology.

Winning is the essence of racing. Thus, in winning the race, the team could prove that its technology was superior. Hence, there was no significance in creating a machine that was not capable of winning. That would lead neither to technical progress nor to the fostering of outstanding new talent. However, the Honda NR development team knew that to make a comeback in the World GP meant the establishment of a training ground for young talents; people who would strive to improve their skills through the creation of truly great motorcycles. If there were no chance of winning the race or fostering talent, Honda would be better off not trying at all.

Honda's answer was the adoption of an oval-piston design. With eight valves lined up atop the pistons, each supported by two connecting rods, the team's new 4-cylinder engine looked like an 8-cylinder. According to Fukui's calculation, the engine could potentially reach a maximum speed of 23,000 rpm and output of 130 horsepower. Therefore, the target output was set accordingly, at 130 horsepower.

However, the oval-piston design necessitated an extremely difficult manufacturing process, in which machining accuracy would be more critical than ever. Of course, no such design had been adapted for use in a high-performance racing machine. Nevertheless, the spirit of Honda was never to be pessimistic, and the team decided it was worth trying as long as there was a real possibility. In making such a decision the team was well aware of the difficult path ahead. In order to beat 2-stroke engines, they had to transcend common-sense thinking and bring in daring new technologies.

The concept for Honda's new engine was finalized in April 1979, and the NR Block set as its primary goal the realization of an oval-piston engine. The team faced difficulties right from the start. In fact, they had to prove that oval pistons, cylinders, and piston rings could actually be made. They also had to find a manufacturer that could help them do it.

Finally, the team commissioned the production to an associate company, Honda Metal Technology, located in the city of Kawagoe, Saitama Prefecture. Development went forward there, but the process was not entirely free of problems. Since in an oval piston a semicircular curve has to merge into a straight line, continuous curvature could not be maintained and edges were created along the piston. This made machining very difficult. Similar problems were found in the honing of the cylinder's inner diameter, and many hours were spent in production.

The team members in charge of engine design had their own private concerns, but spirits were high in the NR Block, where team personnel worked eagerly to prove that their engine was more than a fantasy.

In July 1978, three months after the start of production, the NR team finally completed a dual-valve head, 125-cc single-cylinder engine prototype, which they named "K00." Contrary to the team's concerns, the engine turned properly on the bench tester. With renewed confidence, the NR Block continued its efforts and the following October completed an eight-valve head, water-cooled, single-cylinder engine, the K0. Each day was spent making a prototype, testing it, modifying the specifications, and testing it again. Repeated testing revealed that the oval-piston design would cause problems at speeds in excess of 10,000 rpm, due to poor machining accuracy and the loss of durability. Regardless, the team members knew they could not continue testing single-cylinder engines indefinitely.

The NR Block was in fact developing a 4-cylinder engine commensurate with the testing of single-cylinder units. In April 1979, they completed a 4-cylinder V-engine called the "0X," which was to become the heart of the NR500. During the bench test, the engine produced 90 horsepower, making it clear that they had not yet reached their target of 130 horsepower.

The NR Block had also formed a new materials group in order to study two key problems-machining accuracy and durability. The group leader was to be Yoshitoshi Hagiwara, then chief research engineer in HGA's Third Research Block, who had been collaborating with the development team since the early stages of development. One of the group's key responsibilities was to collect the engine parts broken during testing and investigate their causes of failure. It was a tedious task in which it was often necessary to go through the pieces of several parts one by one and divide them into rings, valves and so forth. The group even studied new materials such as carbon and complex high-tech materials, along with enhanced manufacturing techniques that might be used to build parts which could withstand high engine revolutions. Ultimately, these efforts were fruitful, producing notable improvements in durability.

It was not just the engine that was unconventional. To increase its competitiveness, the NR500 also employed a frame technology that was simply unheard of in the conventional realm of engineering.

Tadashi Kamiya, a research engineer in HGA's Third Research Block who had joined the NR program in the summer of 1978 as chief of the test group for completed product, proposed several ideas that he was thinking could be adapted for use in production cars. One of them was an aluminum frame called the "shrimp shell."

The shrimp shell, which integrated a monocoque structure with the cowling to form the frame and body, virtually encased the engine, which was then inserted through the rear like a cassette. The engine was fixed with 18 six-millimeter bolts inserted at both sides. Although the panel was paper-thin at just 1 mm, once the engine was in place the frame was able to ensure the required rigidity. Additionally, the frame weighed just 5 kg, which was about half the weight of an ordinary tubular steel frame.

The idea, not surprisingly, encountered outright confusion among the members of the NR Block. In order to convince his colleagues Kamiya created a prototype model and, the members understood the concept of his shrimp-shell frame.

The second idea involved the wheel. Kamiya thought of adopting a 16-inch wheel instead of the mainstream 18-inch wheel.

"By reducing the tire diameter," Kamiya said, "we could reduce the machine's weight by around 4 kg and vehicle height by around 5 cm. The lower air resistance and smaller disc diameter also contributed to a lower moment of inertia, enabling the machine to accelerate faster. Moreover, the reduced frontal projection had the effect of increasing output by several horsepower.

"When I compared the 18-inch wheel with the 16-inch wheel, I asked myself which of the two would cross the finish line first in actual races, where average speeds often exceeded 200 km per hour, I was convinced that the 16-inch wheel had greater potential, not simply from the standpoint of partial speeds at corners but by putting all the elements in proper perspective."

Kamiya also adopted a vertical standing screen to be attached to the cowling, instead of the regular semispherical type.

"You could call it an invisible cowling," he said. "With this design we can still achieve sufficient aero-dynamic effect. Since the wind is directed upward after hitting the screen, the rider is subjected to less wind resistance at high speeds. Also, the area of frontal projection becomes smaller."

Another idea involved the swingarm and drive sprocket, which were positioned along the same axis. Because chain length was no longer affected by the upward or downward movement of the swingarm, there was no need to provide extra play. This meant an advantage in reducing shock due to acceleration or deceleration, thus stabilizing the suspension's performance over an entire course.

Kamiya believed that no 4-stroke engine, regardless of its merits, could win with a frame design based on conventional thinking. Thus, the NR's frame was constructed from the standpoint of minimizing volume and weight. The staff sought to create a 125 cc frame capable of carrying a 500 cc engine. These were just examples of the many unconventional, even outrageous, ideas being implemented in the new machine. However, they were all based on strategies that had been calculated to an absolutely meticulous degree.

The NR500 was put to the first test ride in Yatabe, Ibaragki Prefecture, in May 1979. Although the road test brought up problems that the team had failed to identify in bench testing, these were gradually resolved through refinement of the engine in repeated tests at Suzuka Circuit and on the course at Tochigi. The NR500 became more complete with each passing day, and soon it would be ready for its first World GP event. Due to a significant delay in the NR500's overall development schedule, though, its comeback had to be pushed back to the British Grand Prix, which was to be held at Silverstone on August 12.

The NR500 was at last completed in July 1979. Equipped with a 4-cylinder V-engine and 100-degree cylinder banks, the machine had a maximum output of 100 ps at 16,000 r.p.m.

The NR team had finally made it to England, where the machines were receiving their final tuneups in preparation for the GP race. At the same time, Yanase was making various arrangements in order that the team might concentrate on the race free of hindrances. Thus, in addition to setting up the bikes for optimal performance on the track, there were many other things that had to be done for each race, such as arranging transportation and accommodations for the many staff members involved. The World GP, often referred to as the Continental Circus, had most of its races in Europe. Therefore, while it was possible to develop the motorcycles in Japan, it was impossible to manage the races from Japan. The distance was simply too great.

Yanase rented a warehouse in Slough, an English town near Heathrow International Airport, as their team's base of operations in Europe, while in Britain additional preparations were underway through a company called HIRCO (Honda International Racing Corporation). Honda had established HIRCO in December 1978 as a joint venture with Honda UK for the management of all racing activities, including competition in the World GP series.

Honda's riders for the 1979 season would be Mick Grant and Takazumi Katayama, the latter having competed in the 1977 World GP series as a privateer, where he ultimately won the championship title in the 350-cc class.

For their part, the NR500s kindled great expectations upon their appearance at Silverstone, portending awesome performance with their original engine design and sleek styling. However, those expectations were mercilessly shattered in the qualifying round. These bikes, which were still in development, barely performed well enough to get through to the final. Even then, Grant fell at the first corner following the start and quickly retired. Katayama also retired after several laps due to ignition problems.

Though they had not expected a win in their very first race, the NR team was deeply disappointed with the outcome of their efforts. The NR500s were brought back to Japan, and improvements were made to further reduce weight and increase output. However, those really were not the fundamental solutions that the project team had long sought.

Harsher realities awaited in the French GP, the twelfth race of the 1979 season where both machines failed to qualify for the final, meaning that no results whatsoever could be garnered from their presence. However, the team could not go back to Japan without data, after having spent so much time and money in preparation for the French event.

Therefore, the staff of the NR Block flew to England, and with help from HIRCO tested the NR500s at Donington Park. The test was a fruitful one, in which new areas of possible improvement were identified. However, there was no improvement in speed, and the machines were still running two seconds behind the lap record. In the world of racing, where one-hundredth of a second determines the winner, two seconds was just too great a handicap.

Having finished the 1979 season with disappointing results, the NR500s had two major problems that were considered unique to 4-stroke engines.

First, was the factor of extreme engine braking. When development began, the team viewed engine braking as an advantage, believing it would assist in overall control of the bike. On the contrary, the engine braking caused the rear wheel to hop. To counteract it, the team developed a back-torque limiter with a built-in, one-way clutch so that the wheel would spin when the force applied to the wheel exceeded a certain level. This methodology was later incorporated in the VF750F, making it the first production bike to be equipped with a back-torque limiter.

Acceleration was the second problem. It simply did not provide the necessary subtlety of control. The ability of the engine to generate ample low-end torque-a characteristic of 4-stroke engines-also made cornering control difficult, resulting in the loss of time. During the 1980 season the team experimented with throttle pulleys based on various shapes, but as yet there was no solution.

Weight was another area in need of attention. Although the first 0X engine was lighter than the average 2-stroke engine, weight gradually increased as durability improved. Before long, the engine had put on as much as 20 kg. The development team conducted an exhaustive review of materials, going to titanium and magnesium in order to achieve weight reduction. However, the new material combination was quickly copied by rival teams, leaving Honda with no advantage in that area.

The shrimp-shell frame, which had so greatly contributed to weight reduction, also had a drawback. Because of its cassette-type mounting structure, the engine had to be removed from the frame in order to perform maintenance. This made it difficult for the engineers to achieve optimal settings within the limited time allowed in the qualifying runs. Accordingly, the team decided to adopt a pipe frame to the machines, beginning in 1980. At the same time, the wheel size was changed to 18 inches.

Ultimately, the problem with the NR500 was that so many new technologies had been introduced that its potential for completion had been compromised. Realizing this, the NR Block prioritized problem areas, placing the top priority on refining the engine. This, they believed, was the most fundamental problem of the bike.

The new and greatly improved NR500s competed in an international race held in Italy. Although it was not a World GP race, Katayama was able to take the podium with a third-place finish. He also put up a good fight in the final round of the British World GP, held that August. The fifteenth bike to pass the finish line, his machine was the first NR500 to finish a GP race. Moreover, Katayama made a strong showing in the West German Grand Prix, finishing in twelfth place.

The 1980 season, however, closed with just two events in which Honda's NR500s made it to the final round. Still, the machines were making steady progress, so it was still possible to build a point total and finish the season in tenth place or higher. However, the reality was that they were still trailing the 2-stroke machines by 10 or more horsepower. Therefore, even if the NR500s could advance in the standings, they did not have what it took to win a GP race.

Yanase recalled a sentence in the plan document he had received in December 1977. It read, "Become the world champion within three years." He knew that 1981 would be the final year in that attempt, so there was not much time left.

The oval piston engine underwent further improvements in order to reduce its weight, enhance output, and improve durability. The improved engine intended for the 1981 season had a smaller body, made possible by dropping the V-bank angle from 100 degrees to 90. Moreover, it had a maximum output of 130 ps at 19,000 rpm. Therefore, beginning with the 1981 season, Honda decided it wouldn't just compete in the World GP, but that it would also enter the All-Japan Championship Series. Honda made the decision to refine its NR500s more rapidly through participation in more races, hoping to build winning machines as quickly as possible.

In the second race of the All-Japan Championship, held at Suzuka Circuit in March 1981, the two NR500s ridden by Katayama and Kengo Kiyama both fell and retired. However, they had demonstrated considerable tenacity during the race, advancing to a point just behind the top group. In the next race held at Suzuka in April, the team saw one of its NR500s finish in fifth place. By this time, the NR500s were performing at levels equal to those of their 2-stroke counterparts.

Yoichi Oguma, the chief research engineer from HGA's Second Research Block who had joined the NR project in 1981 and became the first manager of the Honda Racing Team (HRC) the following year, had one vision: "Tactics and strategies also are important in winning the race. Honda is so preoccupied with the performance of its machines, but we can't win unless the machines, the riders and the team work as one."

This was a conviction that Oguma, a former All-Japan champion in the 125 cc junior class, had acquired through his own experience. Reflecting on that belief, the Suzuka 200-km Race-the sixth All-Japan race held in June 1981-was run under his careful supervision, according to a calculated strategy.

Any 2-stroke engine running a distance of 200 km, or 34 laps of the Suzuka Circuit track, will require at least one pit stop in order to refuel. That means approximately 10 seconds in the pit area. Considering that the bike must decelerate to enter the pits and accelerate again on its return to the course, nearly 20 seconds must be given up. Oguma's strategy was to let his machines run the entire race without a fuel stop by making use of their higher fuel efficiency, which was of course the advantage of 4-stroke design. According to his calculations, the NR500s would save around 0.6 second per lap by eliminating the fuel stop.

The race was carried out according to plan. While the rival machines were making their fuel stops, Kiyama's NR500 gradually advanced, eventually passing the leader on lap 23. It was the first time an NR500 had led a race. What's more, Kiyama maintained his time, leading the race lap after lap. Coming out of the last corner first, his NR500 kept its lead and took the checkered flag. Three years after the start of development, the NR Block and its NR500 had achieved a victory.

The team was again victorious in July, when Freddie Spencer rode his NR500 to a first-place finish in a five-lap heat race held at Laguna Seca in California, which doubled as the qualifying round for an international race. It was with these victories that the NR500s were established as contenders in the ultimate challenge: to win a World GP race.

It was, however, still quite premature to assume that victory in a World GP event was theirs for the taking. That was too high a mountain to climb. After Katayama's thirteenth place finish at the first Austrian Grand Prix in April 1981, the riders continued to retire from subsequent races. The 1981 season ended without any point total for the Honda team.

Hence, the promise to become the world champion within three years was broken. The NR Block had found itself at the crossroads of victory and defeat, survival and abandonment

Source world.honda.com