Every year when the new models are released, I find it interesting to see what the off-road side has for new developments, and how that compares with what's new in the sportbike world. As you'd expect given the different intentions of each model, the off-road bikes are further ahead in some areas while sportbikes hold the upper hand in others. And in certain aspects, the development of sportbikes is following a similar path to that of the off-road bikes.
Some examples: Yamaha's YZF open-class motocrossers were the first to use titanium valves, several years before we saw them on a sportbike. But it's only now that fuel injection has made its way to the Honda CRF450F, almost a decade after it was used on the CBR929RR. BMW recently introduced the G450X, an off-road bike that features similarities to the K-series sportbikes, such as a perimeter frame and forward-canted cylinder block, and cited similar benefits. Perhaps on future BMW sportbikes we'll see some of the G450X's other innovations, which include a swingarm pivot concentric with its countershaft. We typically benefit from the dirt side for new suspension ideas (although Showa's BPF is a bit of a surprise), while sportbikes generally have more exotic brakes than the 'crossers.
With the recent concentration on off-road four-stroke engines, we can usually look to the latest dirt bikes for a glimpse of what may be in the future for sportbike riders. Case in point is the engine shown here, from the new Husaberg FE450 off-road enduro. The engine's cylinder is at a 70-degree angle, with the crankshaft almost directly on top of the transmission shafts. The company claims that moving the crankshaft closer to the motorcycle's center of gravity makes for a lighter-steering package, and initial reports from the bike's intro are that it does in fact steer quick and feel light for a 450cc off-road bike.
When the Husaberg was first introduced, several magazines pointed out that Kawasaki has a patent application for a similar engine. The application, submitted in late '06, is titled "Engine for a Leisure Vehicle" and shows the engine layout used in on- and off-road applications as well as in a four-wheeler. The Kawasaki version is quite similar to the Husaberg's, with the crankshaft directly above the transmission and the cylinder block positioned almost horizontally.
Benefits of the layout are numerous: With the crankshaft higher and more rearward, and the cylinder head more forward and lower, the center of gravity of the entire engine is similar to that of a more conventional layout. However, because the heavy crankshaft is closer to the engine's CG, improved mass centralization (for the engine itself) allows lighter turning. Additionally, the engine is easier moved with less effect on the motorcycle's overall center of gravity, allowing more leeway in packaging.
With the crankshaft tucked between the frame rails, the bottom of the engine is only as wide as the transmission, improving aerodynamics and ground clearance. Vibration is not reduced, but because the cylinders (and the pistons' movements) are horizontal, that vibration is felt by the rider less than a vertical vibration, meaning a counterbalancer may not be required when in a conventional layout it may be.
With all the space where the crankshaft used to be now cleared out, that room can be used for other components. The exhaust pipes do not have to bend as much (nor do the intake ducts and ports), improving efficiency. The newly open space allows more air to flow through the radiator. And the catalytic converter can be located closer to the exhaust ports, also working more efficiently.
Downsides? None are listed in the patent application, but there are a few stumbling blocks. One is that in the new layout the crankshaft will take away some fuel capacity. Another is that the rear of the engine, right where your knees generally go, is wider. With a single-cylinder engine the width is not such an issue, but on a four-cylinder bike it certainly would be. One way that Kawasaki addresses this in the patent application is by running the camshaft drive from one of the transmission shafts at the front of the engine rather than from the crankshaft, reducing width somewhat.
This engine layout does contradict what is seen in Kawasaki's ZX-RR MotoGP bike, which has a very tall engine that is short front-to-back and has almost vertical cylinders. You would think that MotoGP would be a perfect application, but obviously there are other aspects to the design. It has been indicated to me in the past that yaw moment (the bike's moment of inertia around an axis vertically through the center of gravity) is just as important as roll moment (where the axis is horizontal, from front to back) especially in MotoGP, and the current ZX-RR layout looks to favor that requirement.
Production bikes are different from MotoGP bikes in other aspects, however, and it will be interesting to see if the Engine for a Leisure Vehicle ever makes it into a production Kawasaki. From what our Dirt Rider friends say, the Husaberg is a pretty special piece, and a similar advancement in sportbikes would be a major shakeup. For this year, however, there are still plenty of interesting developments in the sportbike world to keep us entertained, such as crossplane crankshafts, big piston forks and the like.