Honda’s development engineers wanted to create the purest, most enjoyable midsized four-cylinder performance possible for the CB650R rider, so the 649cc, DOHC 16-valve engine has been tuned to ensure a smooth, linear torque delivery that builds strongly as revs rise, and sounds great in the process.

Direct cam actuation makes for a compact cylinder head; compression ratio is raised from 11.4:1 to 11.6:1, and the combustion-chamber shape is optimised by use of a revised piston design. The valve train has been reinforced and valve timing revised; iridium spark plugs are also now employed. Asymmetric piston skirts minimise bore contact, reducing friction. Ferrous spines on the outer surface of the cylinder sleeves reduce oil consumption (and friction) with improved heat transfer, and a silent SV cam chain reduces frictional losses by using a Vanadium coating on its pins. Internal water channelling from the cylinder head to the cylinders does away with most of the exterior hoses.

New twin air ducts on either side of the fuel tank feed a larger volume of air, as opposed to the single, central duct of the old model, raising atmospheric pressure in the airbox. They also produce a throaty intake roar. The exhaust now features a larger bore tail pipe inside the muffler to flow more gas and, with its exit pipe angled upward, to emit an emotional howl. The engine uses a compact internal architecture, stacked six-speed gearbox and starter layout with the cylinders canted forward 30°. An assist/slipper clutch is a new addition and eases upshifts while managing rear-wheel lock up under rapid downshifts. Honda Selectable Torque Control (HSTV) manages rear-wheel traction; it can be turned off should the rider choose.