[Moto] The McLaren F1 of motorcycles? Oval pistons, eight valves per cylinder and more than 200 patents

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If we talk about top-class sports bikes, it is inevitable to talk about Honda. The company founded by Soichiro Honda built a golden reputation in the world of two wheels, and Honda itself saw itself as the technology leader in the sector. In 1992, Honda launched the equivalent of a two-wheeled McLaren F1 or Bugatti Veyron on the market. A limited production motorcycle so technically and mechanically advanced that nothing like it has ever been developed again. This is the story of the Honda NR750.

Before getting into flour, you have to remember that Soichiro Honda hated two-strokes. They seemed noisy, unrefined, and technically inferior to his refined four-strokes - on which Honda has built its reputation since the 1960s. In 1979, Honda once again competed in the premier category of motorcycling, the 500 cc category. A category dominated then by very powerful motorcycles with two-stroke engines. Soichiro Honda did not want to stoop to that level.

To date, Honda had won a multitude of Grands Prix and competitions such as the Isle of Man Tourist Trophy with four-stroke engines. And that is why it returned to the premier category of motorcycling with a four-stroke engine. To match the power of the two-stroke engines in its Honda NR500, the Japanese brand began development of a revolutionary oval piston engine. The starting point was the championship regulations, which forced the motorcycles to have four-cylinder engines.

For a four-stroke engine to achieve the 120 horsepower of a two-stroke engine, it must spin twice as fast. For this, the engine had to have unparalleled thermal efficiency and had to "breathe" very well, since the calculations of the engineers estimated the engine's speed at 23,000 rpm. To do this, they decided to increase the number of valves per cylinder to eight and to make all the pieces fit in the puzzle, to manufacture an engine with oval pistons, a solution never seen before.

 

Each piston had two connecting rods, and although it had four cylinders, the powertrain resembled a miniature V8. Honda New Racing (NR), the division in charge of developing the engine, had to perfect machining precision to the micrometer and raise production quality to the limit of what is physically possible, with tolerances never before seen in the world of combustion. internal However, the competition debut in 1979 - at Silverstone - of these engines was a real disaster, and was plagued by serious mechanical problems.

Honda did not give up its efforts, and despite the defeats, in 1983, the power of the oval engines already exceeded 130 CV and was at the level of two-stroke engines. Unfortunately, the weight of the engine was still a limiting factor, despite efforts to lighten it using materials such as titanium or magnesium. Honda's management was beginning to get nervous, and in order to achieve victories again, Honda had to "downgrade" to two-strokes, creating the highly successful NS500 and NSR500, which returned the brand to winning ways.

 

The Toshimitsu Yoshimura team continued to evolve Honda's oval engine, and by the late 1980s, they were still committed to producing a competitive race bike. The NR750s didn't do poorly in drag racing, but they were still not dominant bikes. Still, Honda had blind faith in their engine, and five years after the last NR750 races, they wowed the world with a technological tour de force.

From the ashes, the NR750 is born, the best motorcycle in the world
Undercover, and without making noise, in 1992, Honda presents the world with the NR750. A spectacular street bike with a strict limited run. Only 700 units were built, selling for $60,000 in the United States at the time - almost $130,000 adjusting for inflation. This bike not only powered a civilized and perfected version of Honda's oval engine, but followed more than 200 patents and technological innovations, many of which have been modified to today's standard in top-class sportbikes.

1992 this bike had more advanced technologies than many cars. It was the two-wheeled equivalent of a McLaren F1.
The oval engine was the undisputed protagonist, yes. It had 748 cubic centimeters, eight valves per cylinder, oval pistons, and two connecting rods per cylinder. The connecting rods were made of titanium and each combustion chamber had two spark plugs and two throttles, with two throttle bodies. The bike used PGM-FI electronic fuel injection and the intake manifold was a complex piece of plumbing, in the scheme 8-4-2-1-2, although from the outside only two exhaust pipes could be seen under the fairing. rear.

Its power was 125 hp at 14,000 rpm and its top speed was 263 km/h. At the time, and due to their displacement, they were stratospheric figures. But this bike not only impressed on a quantitative level, but also for the quality and avant-garde of its running gear, laying the foundations for what would be the sports bikes of the future. Many of its innovations have never been seen on a street bike before. At that time, even the most advanced sportbikes were still using elements that were already obsolete, such as carburetors.

 

It mounted a 45 mm inverted fork - at the time, reserved for competition - or two 310 mm brake discs with four-piston Nissin calipers. Its wheels were magnesium, 16 inches in front, and 17 inches behind. Its bodywork was a combination of fiberglass and carbon fiber. Its instrumentation combined analog clocks with a digital display, framed in a beautiful carbon fiber molding. Its Showa suspension was fully adjustable, its radiators were positioned to the side, and its headlights were asymmetrical.

The build quality of the bike was of the highest level, a reflection of Honda's intention to show the world what it was capable of. A punch on the table that suddenly woke up the rest of the motorcycle manufacturers. The NR750 was born as a collector's item, but its technical advances can still be felt today in the world of two wheels, which was thrust - violently and suddenly - into the future by this bike.

 

Link: https://www.diariomotor.com/noticia/honda-nr750-historia/