Honda RC166

The Honda RC166, also known as the Honda 6, is a Grand Prix racing motorcycle that Honda raced in 1966 and 1967, a technologically advanced 250 cc DOHC air-cooled inline six. On it Mike Hailwood took the 250 cc riders' championship and Honda the constructors' championship in both years it raced, and it evolved from the earlier 3RC164 and RC165. After the inline-four RC164 was no match for Yamaha's RD56 in 1964, engineer Shoichiro Irimajiri, then 24, began design in January 1964, completed the first sketches in February and had a running engine by June. Two-stroke rivals get a power stroke every crankshaft rotation and a four-stroke only every two, so Honda answered by making the four-stroke rev much higher, using more cylinders to keep reciprocating weight low.