Years ago, those guys at Honda were my heroes because they overcame established concerns by offering technology as a weapon against arty tradition. I was offended then (and I am today) by what I call "lost chord theorists", who propose that there is some ineffable, undiscoverable quality about, say, an MV or Ducati, which confers upon it special value and status. This special value lies in a realm not accessible to any kind of objective testing -- acceleration times, laptimes around a circuit, all such real-world tests are irrelevant.
At any rate,the lost chord fellows were regularly confounded in the 1960s by the success of machines that were merely excellent, rather than grandly traditional.
On the other hand, that excellence was being dipped from a well of strictly limited depth. As Honda's engineers raised the RPM while multiplying cylinders, the BMEP of their engines fell steadily (BMEP is Brake Mean Effective Pressure, a stroke-average of combustion pressure). To make crankcases and other parts able to contain the rotating and vibrating parts, these had to be made quite heavy. To obtain adequate acceleration while toting all this extra metal, the Honda people essentially took away the crankshaft, making rotating mass so tiny that these engines were not easy to ride.
In the middle period, Honda had excellent success with this compromise between power rising because of higher RPM, and power falling because of reduced BMEP. In comparison with the poor two-strokes of the middle 1960s, such machines as the Honda 250 six were truly excellent. They had wide power, adequate acceleration, and great reliability (provided that their continuous nemesis, high oil temperature, was under at least marginal control -- those dense masses of aluminum were real heat traps, and oil was a very important vehicle in freighting that heat out).
While the two-stroke makers refined their arts in the 1970s, Honda tilted at Formula One success. When Yamaha's efforts to take away their status in motorcycling finally awakened the company, one of the first things it did was to rekindle efforts to win GP races with some kind of four-stroke engine.
That four-stroke engine was the NR500, and it proved that the old limitations and lack of well depth were still in force. The engine was heavy -- had to be heavy -- because of all the whanging and banging inside it, because of the multitude of parts, because of the sheer volume required to encase it all. One of its first riders, Mick Grant, said the bike felt as if made of lead. Its friction ate its power, despite refined efforts to cut parts weight and "oil-swept area". The oval, eight-valve combustion chamber was unique among engines with a lot of piston area in that it could burn its charge fairly quickly, being in effect just two round chambers, each with its own central spark plug. Freddie Spencer rode the bike, too, noting a wide powerband, somewhat lacking in acceleration. At best, 136 BHP were extracted from the concept -- not too much more than twice what was had from the 250 cc six so many years before.
Two basic views are possible. One is that Honda has shown great resource in extending the basic concept of the atmospheric four-stroke engine to new realms of specific power. Another sees the oval piston as a monument to an idea developed beyond its scope -- rather like the last, monstrously complex piston aircraft engines. A better concept was already afoot -- the gas turbine -- but the piston-engine establishment had to make its final statement. In retrospect, those monsters seem fallen monuments to an overthrown order.
Is that the fate of Honda's NR engines? To be seen as grand achievements from another era or paradigm? And will we in time look upon them as I did upon the MVs of the 1960s -- as tradition without enduring merit?