Kawasaki Patents Point to Supercharged Four-Cylinder SxS

On January 23, 2024, Kawasaki will take the wraps off its all-new Ridge side-by-side—a machine that’s already confirmed to feature a four-cylinder gasoline engine—and the company’s patent activity hints that it could be even more exotic and use a variant of the company’s unique supercharged H2 motorcycle engine.

Patents first filed in 2021 but not published until this year show several designs for a supercharged side-by-side. They’re illustrated in a utility-style vehicle similar to the Mule, but that’s likely to be a red herring: The high-performance, supercharged four is clearly better suited to a sport vehicle.

While the engine is a fairly conventional, DOHC four-cylinder, the addition of a crankshaft-driven supercharger sets it aside from the norm. The supercharger itself is a centrifugal design, using an impeller similar to a turbocharger’s rather than the Roots or screw-type positive-displacement superchargers that are more commonly found in automotive applications. That means it will build boost as rpm rises, with little effect at low engine speeds but the potential to offer more boost and higher power at the higher reaches of the rev range.

The patents actually illustrate four distinct versions of the supercharged powertrain, each taking another step up the performance ladder. The engine shares its general design with the 998cc supercharged H2 engine used in Kawasaki’s Ninja H2 supersport bike, Z H2 roadster, and Ninja H2 SX sport-tourer. It’s not an identical engine though. The supercharger, for instance, is driven by gears from the crankshaft where the motorcycle version uses a chain drive, with a chain-drive version mentioned only in passing as a potential alternative for a particularly high-performance iteration of the engine.

As on the H2 motorcycle engine, a planetary gearset massively increases the speed of the supercharger’s impeller. Kawasaki’s patent says that in the form illustrated, the impeller will turn eight times as fast as the crankshaft, which is actually a little less than on the motorcycle versions, where the impeller spins 9.2 times as fast, reaching as much as 130,000 rpm.

The four versions of the engine shown in the Kawasaki patent start with the least powerful, lowest-cost iteration of the idea. In this form, the pressurized air from the supercharger is fed through a single, large throttle body and directly into an inlet manifold that distributes it to each of the four cylinders. As well as being used in most of the patent illustrations, this setup looks closest to the snatched glimpse of the engine shown in the teaser video for the Ridge side-by-side—a shot that shows the spark plug–mounted ignition coils of four cylinders emerging from a cam cover, with what looks like an intake runner visible on the left of the image.

The second iteration of the engine shown in the patent features four individual throttle bodies, with the supercharger feeding air directly into a pressurized plenum chamber above them. This is essentially the same system used on the motorcycles with the H2 engine, where the rapid throttle response and peak power advantages of the individual throttle bodies are combined with the tight packaging constraints of a motorcycle.

The third version of the engine illustrated in the patent swaps back to a single throttle body leading into a four-branch intake manifold but adds an air-to-air intercooler between the supercharger and the intake, cooling the intake charge, making it denser so more can be forced into each cylinder during the intake stroke. Kawasaki’s motorcycles go without an intercooler, as it’s relatively bulky, but it’s a system that would be easy to fit to a side-by-side for an immediate performance increase.

Finally, the fourth version of the engine combines the intercooler and the four individual throttle bodies, as well as swapping to chain drive for the supercharger, with the intention of maximizing outright power. All the engine variants shown in the Kawasaki patents are connected to a CVT transmission, another substantial change from the motorcycle version that has a six-speed sequential manual box.

Speaking of power, how much might this supercharged engine make if it really does reach production in a future side-by-side? That’s hard to judge, as so much depends on the boost level of the supercharger, but the H2 engines in Kawasaki’s motorcycle models range from 197 bhp in the Z H2 and Ninja H2 SX to 306 bhp at 14,000 rpm for the non-road-legal Ninja H2R. For a side-by-side, any engine is likely to be retuned with a greater focus on low-end torque, so the outright peak power would probably be lower. It will still be vastly more than the 112 hp offered by the most powerful of Kawasaki’s current range of side-by-sides though.

Will the Ridge really use this supercharged engine? Well, there’s already one side-by-side in existence that features a version of the same motor, the one-off HySE-X1 that’s been developed in Japan by the “HySE” consortium of manufacturers including Kawasaki, Honda, Yamaha, Suzuki, and Toyota. “HySE” stands for Hydrogen Small Engine, and the group is focused on developing hydrogen-fueled combustion engines for future vehicles including motorcycles, ATVs, and side-by-sides. The X1, revealed in October at the Japan Mobility Show, is intended to compete at the Dakar Rally, running from January 5 until January 19—just days before the Ridge is due to be revealed—and uses a version of the Kawasaki H2 engine that’s been reworked to run on hydrogen rather than gasoline.

Another tiny clue that the Ridge just might use the supercharged engine comes in the form of the mirrorlike paintwork that’s shown in Kawasaki’s teaser video. This looks very similar to the dark chrome finish Kawasaki created for the Ninja H2 motorcycle when it debuted back in 2014 and uprated in 2019 to a “self-healing” version, with a topcoat that remains slightly fluid, leeching back into small scratches so they disappear after a few days, particularly in warm temperatures.

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