The Honda CB450
was the first "big" Honda motorcycle
with a 444cc dual overhead cam engine
producing 43-45 horsepower
(more than 100 HP/ litre). Appearing first in the 1965
four-speed K0 model, and progressing through a series of KX models with various improvements and styling changes, notably a redesigned gas
tank and 5 speed transmission
in the 1968
K1 model. K0 models are often known as "Black Bomber" models in the U.S. and notable for their distinctive large, square gas tank. In Canada the K1 model was actively marketed as a HELLCAT.
Although the CB450 never sold up to Honda's expectations, it had excellent engineering for the time, notably including reliable electrical components, an electric starter, and a horizontally split crankcase, all features distinct from the British twins of the era. The most radical feature was the valve springing. Instead of the conventional coil spings it used "torsion bars" - rods of steel that twisted to provide the spring effect.