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THE FOUR-STROKE/
TWO-STROKE WARS
Remember when debates raged about which fundamental
design would prove superior for Grand Prix racing, four-stroke
engines or two-strokes? We're not talking 2002, when rule
changes gave manufacturers the option of running two-stroke
engines of 500cc or less or four-strokes up to 990cc in their
GP machines. That deck was loaded in favor of the four-
strokes, and morphed into the MotoGP era we have today.
Rather, we're talking about the middle 1960s, when that
key question turned into a technological battle between
two-stroke and four-stroke 125cc race bikes. No special
allocations or dispensations allowed—just bring your best
eighth-liter bike to the track and we'll settle things at the
checkered flag.
In 1961, 1962 and 1964, Honda four-strokes won three
125cc world titles, but by the middle 1960s two-strokes
had evolved into an undeniable force. Debates surrounding
engine design had real merit: In a two-stroke engine every
crankshaft rotation yields a power stroke, while four-strokes
produce power only upon every other crankshaft rotation—
one rotation is "wasted" pushing out gasses. There is no
shortcut here; to produce equal power in a four-stroke, engine
speeds must increase substantially.
The obvious answer to this dilemma was to create an
engine with more cylinders. But they would have to be tiny
bores combined with an extremely short stroke to allow ultra-
high engine speeds—all of which invited disaster given the
materials and technology of the day. But Honda did it.
