Though we were hopeful that the changes to the engine might bring a solid kick in the pants when we hauled on the throttle, engine performance is about what we anticipated. The 1670cc version of this engine ("the largest air-cooled V-twin," Yamaha reminds us) pulls harder and turns more rpm (5200 to 5700, depending on the gear you're in) before bumping gently up against the rev limiter than the 1602cc mill, which signs off at 4200 rpm. Yamaha tweaked the power delivery so that there is a slight surge as revs build. Though you don't notice it particularly, the power delivery is probably a bit more dramatic than if torque built in a nice, smooth, barely curling line. However, the sensation is smooth power delivery, increasing steadily with engine speed. The engine retains that under-worked feeling of the Road Star, and some riders said that the speed just sneaked up on them, frequently surprising them when they consulted the speedometer. Between the shortened gearing and the added power, acceleration is impressive, and to folks like us who feel that there is no such thing as too much power or acceleration, the added boost is a definite plus. It noticeably shortens passing distances, lets you squirt away from lights more quickly, and simply delivers more kinetic thrills per gallon.