Kawasaki unveiled its “SC-01 Concept” at the 2016 Tokyo Motor Show, with the display featuring an engine mockup using an inline-four-cylinder engine with a gear-driven supercharger similar in design to the unit on the H2/H2R sportbikes. The company that turned the sportbike world on its ear this year with its supercharged siblings appears to be continuing on that path, with the “Spirit Charger”concept utilizing a smaller-displacement engine not for ultimate performance, but “a machine suitable for all day, long distance enjoyment and comfort,” with “softer, more luxurious materials.” Granted, the styling sketch that was provided shows a bike with a definite sporting bent, but it’s likely that was an early drawing in the beginning stages of the original concept.
What was really intriguing about the SC-01 engine was the supercharger unit itself. It’s the same centrifugal-type supercharger as the H2/H2R models, but mounted on the intake side was a unique adjustable vane setup that controls the amount of airflow into the supercharger (see the animated gif photo below). By electronically controlling the intake airflow, this innovative idea will theoretically help eliminate several of the issues with a direct-driven centrifugal supercharger, namely smooth power delivery, precise boost control, and efficiency at lower rpm.
Normal control of power with a forced induction vehicle is by a throttle plate downstream from the compressor, and boost control through a pressure release valve of some sort. When you close the throttle in a normally aspirated engine, you begin to close off the vacuum that pulls in the intake charge into the engine, reducing power accurately; on a direct-drive forced-induction engine, if you’re closing the throttle while the compressor is approaching full boost levels, it’s still forcing airflow into the engine before the throttle is shut completely, leading to imprecise throttle control. And because the compressor is still forcing air into the throttle body after the throttle plate is shut completely, you need to bleed off that pressure, otherwise you get a “boost surge” condition that can cause damage to the throttle plate(s) and the compressor itself.
By precisely controlling the airflow into the compressor as well as controlling its output, Kawasaki engineers gain benefits on multiple levels. Instead of being forced to compromise on the compressor’s impeller size and design as well as the drive ratio (the speed at which the impeller spins) in order to balance having a smooth powerband and attain proper boost control, all while achieving low-rpm efficiency, the adjustable intake vane setup opens up design specifications significantly. Kawasaki likely had many more choices for impeller size and speed for better low-rpm efficiency (and power) while being able to more precisely control the boost output at higher rpm for a smoother powerband (i.e., you’re no longer stuck with the compressor’s boost vs. rpm curve) and better boost management during partial- and closed-throttle situations.
The SC-01 engine was displayed on a 600cc-size engine, lending further credence to the rumors of an upcoming “S2” model utilizing a mid-size supercharged engine. And don’t be surprised to see more forced induction designs in Kawasaki’s lineup in the future, as the President of Kawasaki’s Motorcycle and Engineering section, Kenji Tomida, hinted that the supercharger concept will continue to be integrated into future models.
On a related supercharged note, if you missed the boat for purchasing an H2 or H2R, fret not; Kawasaki had the 2016 versions of both models on display at the show, with paint and minor ECU updates for both, and the H2 getting the slipper clutch from the H2R.