2015 Harley-Davidson Street 750-Lineup, Urban riding puts its own set of demands on a motorcycle engine. The city grid is no easy-riding, wide open, winding road with beautiful vistas as far as the eye can see. It s a moving mass of stop and go sheet metal with heat waves rising off the pavement on most days. You need an engine built to conquer it. The new Revolution X engine is 749 cubic centimeters of authentic, liquid-cooled, custom Harley-Davidson motorcycle built for urban streets. Liquid cooling means it maintains temperature and performance. Count on smooth response to the progressive throttle when you call on the Harley-Davidson Street 750 motorcycle to get you through any hole that opens up in front of you. But we didn t just build this engine to get you from here to there. This is a Harley-Davidson engine. We built it to satisfy. 60 degree cylinders.