Facing increasingly competitive two-stroke racers in the 1960s, Honda kept developing the four-stroke engine. Its RC166 used six cylinders in the 250 cc class to pursue still higher engine speeds. The motorcycle helped secure both riders’ and manufacturers’ world titles in 1966 and 1967.
The small inline-six packed twin overhead camshafts and 24 valves. Honda’s historical specifications list more than 60 metric horsepower at 18,000 rpm and a seven-speed gearbox. Six individual exhaust pipes also gave the machine its distinctive voice.
The engine’s designer, Soichiro Irimajiri, was just 25 when he worked on the project. The RC166 pictured here was photographed at the Honda Collection Hall in Motegi in 2011. Beneath the slim fairing sits a story of small displacement and intricate machinery: a racing solution that reminds us that cylinder count alone says little about a motorcycle’s size.