The Oval Piston: Heart of a New and Different Breed

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Freddie Spencer gave an awe-inspiring performance at the South African Grand Prix in March 1983. That season, Spencer survived a heated championship race and grabbed his title in the final event. Honda even won the Manufacturer's Championship title, five years following its return to the World GP series.



<< 1. Speeding Through the 1960s
<< 2. After a Decade, a Comeback to the Grand Prix
<< 3. Organizing the NR Block: Preparing for a Comeback
<< 4. Coming Back with a 4-Stroke Powerplant
<< 5. The Oval Piston: Heart of a New and Different Breed
<< 6. From Fantasy to Reality: Completion of the 0X Engine
<< 7. The Unconventional: Adopting a "Shrimp Shell" Frame
<< 8. The NR500s: A Humiliating Debut
<< 9. Refining the Engine-a Top Priority
<< 10. First Victory: The Suzuka 200-Kilometer Race
<< 11. The NS500, Honda's First 2-Stroke GP Machine
<< 12. Victory Again : After Fifteen Years
<< 13. Using Computer Analysis to Bring Honda Back, Stronger than Ever
<< 14. From the NR to Le Mans and Production Bikes
 


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.
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