Kawasaki Ninja H2 SX & H2 SX SE Supercharged Engine | Cycle World
Courtesy of Kawasaki

Kawasaki Repurposes Its Supercharged Sportbike Engine

New Ninja H2 SX and Ninja H2 SX SE boast the best of both worlds: instant bottom torque and the strongest of roll-on passing power

In today’s difficult economy, existing products and technologies must seek wider markets. Further, the market may find new uses for existing products. Honda originally introduced its Gold Wing in 1975 as a new kind of super-performance bike, but buyers soon transformed it into a long-legged touring machine.

Kawasaki’s sensational supercharged Ninja H2 (street) and H2R (track-only) 1-liter sportbikes, introduced in 2014, were intended to get market attention. With its claimed 310 tire-smoking horsepower, Ninja H2R succeeded. Yet supercharging offers possibilities other than sheer speed. Because supercharging makes great torque and power by forcing the airflow of a bigger engine into a smaller, more compact one, it can provide a strong alternative to the huge displacement (and weight) that other makers currently give their big bikes.

Kawasaki Ninja H2 SX stripped view

Supercharged sport-tourer stripped: 2018 Kawasaki Ninja H2 SX SE.

Courtesy of Kawasaki

Kawasaki has now exploited this alternative in a pair of new sport-touring models, the 2018 Ninja H2 SX and Ninja H2 SX SE, which are said to combine “power, everyday usability, and fuel efficiency.” Although press materials call these machines sportbikes, their “redesigned passenger-friendly trellis frame, convenient KQR luggage mounting,” and cruise control reveal that they represent a new kind of sport-touring motorcycle.

How do you reconfigure a supercharged engine for this role? Piston-powered fighter aircraft of WWII needed heavy supercharging for maximum power, but the more mixture you cram into a cylinder, the closer you push it to detonation—a destructive form of combustion. To prevent this, you reduce the compression ratio. This is why the original H2/H2R had its low 8.5:1 compression ratio. Yet fuel efficiency and compression ratio are linked; the lower the compression, the higher the fuel consumption. This is okay in a fighter, for when you firewall the throttle to close on the enemy, fuel economy is not your big concern.

Kawasaki Ninja H2 SX engine parts cg illustration

Ninja H2 SX engine in plain view, from intake funnel to six-speed gearbox.

Courtesy of Kawasaki

But when Boeing’s 314 flying boats introduced New York-to-Lisbon service in 1939, economical long-range cruising was essential. They were therefore given special high-compression Wright R-2600 engines. And in like fashion, the Ninja SX and SX SE have been given much higher 11.2:1 compression. This higher compression gives instant bottom torque, yet combined with supercharger boost can deliver the strongest of roll-on passing power.

Assisting the raised compression are shorter valve timings and higher and slightly smaller intake ports. Maximum cylinder filling is engineered for a specific rpm range in any application. For example, in Harley-Davidson’s classic XR750 dirt-tracker, acceleration off corners was what won a thousand races not blazing top speed. Therefore, like these new Kawasakis, the XR750 was given superbly streamlined high intake ports sized to deliver cylinder-filling high velocity in its midrange.

kawasaki h2 and h2 sx intake port illustration

Higher, slightly smaller intake ports are said to give the H2 SX even better midrange.

Courtesy of Kawasaki

Same with cam timing: When you want acceleration above all, long, peaky sportbike cam timings don’t work. Long timings do make peak power, but at the real-world rpm of highway roll-ons, long timings allow the rising pistons to back pump some of what they just took in, resulting in weakened midrange and bottom-end.

The Ninja’s supercharger, its impeller reshaped for midrange, pushes in extra charge when needed, giving the 1-liter engine the torque of a much larger displacement. Engineering adapts technology to the chosen task.

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