A New Direction
A NEW DIRECTION
ROUNDUP
Not every year does the direction of motorcycle design change. Sometimes motorcycles follow the same design direction for decades with little variation. This year is important. Several new trends are starting, some of which will be more important than others. The most important may not be the various turbocharged bikes being introduced. That's just tacking on hardware that's been around for years. The results may be attractive and reasonably fast, but it's not the most important change. Neither is the resurgence of sports bikes with their tiny fairings and lower bars and bright paint jobs. Those are just another good idea making the rounds again.
No, the most important trend is a new wave of thinking on engine designs, well displayed in two bikes tested in this issue. It’s the Piston Area Special, as English tuner Lawrence Pomeroy called it, and í>oth Yamaha and Honda have ventured into this area of design at the same time and with much the same design. The bikes are the Vision and the V45 Honda.
Both are liquid-cooled engines with a Vshaped engine configuration, big bores and relatively short strokes, both have four valves in every cylinder and both jpake excellent power over a broad range of engine speeds. Both Honda and Yamaha have produced V-shape engines before, Honda with the CX500 and Yamaha with the XV750 and 920. And the Honda 500 V-Twin started some of these trends, but it didn’t go as far as either of the present engines go.
At the core of engine design both these engines are highly oversquare. For the size engine built the oversquare designs provide lower piston speeds and larger piston areas, two good starting points for high output engines.
There have been other oversquare engines built, but most of the better performing motorcycles in recent years have been bikes with a row of cylinders set across the frame. In this configuration a wide bore makes for a wide crankshaft and as a result many of the inline Fours have had surprisingly small bores and long strokes. Some of the solutions used have included auxiliary shafts mounted behind cylinders to eliminate ignitions and alternators on crankshafts, but still the bores didn’t get too big. Engine width was still a problem and adequate engine cooling meant there had to be some space between cylinders of the air-cooled engines. Anglesof the valves in the cylinder heads were also limited by engine height considerations, though Suzuki managed to move the valves together in a small angle by using lever-operated cam followers.
Only through the mixture of V-engines and liquid cooling have the details been solved. V-shaped engines fit nicely into motorcycle frames, which is why that became the standard engine configuration 70 years ago. The engine becomes more compact, and this is a growing concern to a motorcycle industry faced with the prospect of installing emissions canisters on a motorcycle. The continual battle between a low seat height, low engine, adequate suspension travel and a moderate wheelbase all make a compact V-engine an attractive solution.
Liquid cooling is being used more and more to meet sound laws as much as anything. If there is less mechanical noise from an engine, the exhaust can be louder and more pleasing. Also, if the laws change, a company producing a liquidcooled engine can more easily adapt it to the new laws. Liquid cooling enables the V-engines to have exhaust ports running out the back of the aft cylinders without overheating the rear cylinders, something not possible with an air-cooled engine.
More engines are using four valves per cylinder, too. Earlier efforts didn’t always provide an increase in power to go along with the increase in parts, but the new engines are different. The engineers have learned more and are designing combustion chambers that make better use of the better flow. The greater number of smaller valves can also be opened faster and closed faster than fewer larger valves, so cam timing can be more radical. This also means camshafts can have more radical ramp speeds, opening more valve area sooner. This has been a trend for several years on Japanese motorcycles and the new direction will help this.
Carburetor design was stagnant for several years, with CV-controlled sidedraft carbs common on most bikes. Accelerator pumps have been added, but now there are downdraft carbs coming for the new engines, some with accelerator pumps and some, like the Vision’s carbs, butterflyvalve controlled, just like a Weber or Holley carb on a car.
These two new motorcycles are not>
shots in the dark. They didn’t just appear and they won’t just disappear. Where the designs will lead is still a matter of speculation, but a quick look at the age of existing designs and gaps in the product lines could lend some clues.
Honda has already expanded its CX500 V-Twin into a V-Six car engine for Formula Two racing, so it shouldn’t be a surprise to see the V45 expanded into a V-Six for the next generation of Gold Wings. The basic engine has already been enlarged to lOOOcc for the Daytona race, so a lOOOcc version of the existing bikes is a sure thing.
Yamaha can be expected to do some of the same things. The XS1100, now called the XJ1100, is a bit long in the tooth and has been trimmed down to just one model. A llOOcc V-Four version of the Vision would make a super replacement.
What about the other Japanese companies? These are harder to predict. Suzuki was the first Japanese motorcycle company to produce a liquid-cooled motorcycle, with the GT750, and Suzuki has V-Four prototypes, we are told. The next generation of Suzuki four-strokes could be much like the Honda and Yamaha V-engines. Kawasaki makes big splashes in engine design, but not very often. The last new Kawasaki engine design was the 1300 Six, a liquid-cooled design, but one that has not been particularly popular. The Kawasaki Fours have been developed into the fastest and some of the lightest bikes in their class, but it’s about time for Kawasaki to drop another bomb.
There are, of course, the rumors of BMW’s liquid-cooled Four, and Harley’s V-Four. Neither one is scheduled for delivery in 1983, according to the factories, but both are likely to follow some of the design trends of these new engines from Honda and Yamaha.
We wouldn’t put any money on any of this, but it’s fun to dream, isn’t it?
