Whether or not you're a motorcycle fan, or a Honda fan for that matter, it's hard to deny the impressive nature of what Honda accomplished with the RC166. The RC166 produced 62 horsepower, attained a top speed over 150 mph, and did this with a motor displacement of just 249cc., normally aspirated.
That's less than 1/10 the displacement of your average modern-era Mazda 3. To help identify that scale, consider a 12 ounce bottle of your favorite beverage is 355 cc. Drink about a third of it, and what you're left with in your bottle is the displacement of the RC166. And all this in an era without computers, which means no computer-based machining equipment either.
This started in the early 1960s, when the motorcycle Grand Prix circuit was largely a two-stroke engine game. This was largely a result of Ernst Degner leaving then-communist East Germany and motorcycle company MZ, who built quite powerful two-stroke engines. Degner fled to Suzuki, who greatly benefited from his knowledge of the technology, specifically leveraging exhaust pressures and waves. The result was a broad movement toward high output two-cycle motorcycle engines.
Honda would be the exception to that movement. Earlier, Soichiro Honda had made a very public statement that Honda was committed to quieter, cleaner burning four stroke engines. And it waqs well-known that Honda's racing effort existed for the purpose of advancing production design. This created a sizable task for his engineering team -- to create as much power from half as many power strokes.
Their approach was to focus on miniaturization. This would allow them much higher engine speeds with less chance of engine failure. So Honda started developing very diminutive four cylinder four stroke engines.
The approach worked out very well initially. Honda secured the 1962 125cc, 250cc and 350cc world championships and the 250cc and 350cc titles again in 1963.
By 1964, Honda was not able to keep up with the developments of Suzuki and Yamaha and their two-stroke engines in the 250cc class. Honda decided to take the miniaturization idea to another level. For 1965 the RC165 model transformed to six cylinders. Each cylinder was only 41mm (1.6 inches) across the bore, with an even smaller 31mm stroke. The inline-6 occupied the same space as the four-cylinder model it replaced. At only 14 inches across, it was narrower and more compact than the parallel twin offering from Yamaha. The concept of utilizing a six-cylinder engine in the GP series was so unthinkable, Honda went to special efforts to conceal it. And very effectively. They went so far as to ship the motorcycle to its first race in Italy with only four exhaust pipes showing, and the engine under covers. Once the bike was fired up, there was no longer a question it was something different. The sound is truly spectacular. Unfortunately, the RC 165 suffered from reliability issues and needed a better chassis. Those issues would be resolved very effectively the next year with the introduction of the RC166.
The engine in the RC166 is a masterpiece of specific output. If you consider cars with high specific outputs in today's era, there is really still no comparison. Consider the venerable Honda S2000 for comparison; it generates 240 hp from a 2 liter VTEC engine. If you scaled the numbers for the RC166 power plant to the same displacement, it would generate 520 hp. Without VTEC. Without electronic ignition. And it would do it with carburetors.
There is further evidence of the obsessively thoughtful development. The camshafts were created to be barrel shaped — fatter in the middle then they are at the ends — to minimize flexing and help take as much advantage of inertial forces as possible. This means each piston's valves are different length, and unique to it. The crankshaft was handmade from 13 distinct fixture-made parts. All these little weight exercises were critically important considering the bike essentially has no flywheel. This engine is essentially built like a finely built mechanical watch. A watch that makes 62-65 horsepower. And spins over 18,000 rpm.
In addition to its incomprehensible motor, the bike was exceptionally lightweight at under 250 pounds, and was mated to a seven speed gearbox.
It is really no wonder that the RC166 won every race it entered --10 out of 10 -- in the 250cc Grand Prix World Championship series for 1966 in the exceptionally capable hands of Mike Hailwood.
So for those of you that enjoy the efficiently generated output of today's modern-era Hondas, it it worth remembering much of the embodiment of that philosophy started with this little motorcycle.
Petrolicious - RC166
Motorcyclist - RC166