08.13
Unknown
Hard times bring change. Currency shifts are making Japanese goods less attractive, European goods more so.How about American-made goods? Maybe it’s time for a new motorcycle enterprise. Here comes Motus (Latin for “motion”), designed in Birmingham, Alabama, with Made in USA all over it. I spoke with Brian Case, vice-president and Design Director at Motus. When you log onto the Motus website you read, “Engineered in Michigan, designed and built in Alabama.” Engineering is by Pratt & Miller, a firm with 20 years of racing and other design experience, long allied to GM.
I learned that the Motus MST-01 is a 1650-cc V4-powered Sport-touring bike that combines the strong and wide pulling power of a traditional 2-valve V-twin with the all-day smoothness of a multi-cylinder engine. The engine design—and at least its preliminary manufacturing—are by Katech, a Tier 1 GM supplier for 30 years. “When Chevy wanted a 505-hp/100,000-mile engine for its Z06 Corvette, Katech developed it,” said Case. I spoke with Fritz Kayl of that firm about design decisions. He told me that Case and partners wanted an all-American flavor in a V-Four engine. That meant pushrod valve operation and a muscle-car-like “V-Eight look” for the engine. Because Katech has extensive racing (Corvette) and production experience with GDI (gasoline direct injection), that was a natural addition to the package. GDI delivers a denser intake charge that boosts torque.
What is gasoline direct injection—GDI—and why is it suddenly all around us? It’s just what it sounds like—injection of the fuel directly into the combustion chamber, after the air intake event is over.
Beginning a couple of years ago I was hearing that Cadillac’s new CTS V-Six would feature GDI, and when the car arrived its engine was hailed as doing the job of a larger V-Eight with only three-quarter the number of cylinders—equal power, equal torque, but from a smaller, lighter engine. When last Spring I attended the New York Auto Show, there were GDI-equipped autos on display. I noticed that GM’s GDI offerings had unusually high compression ratios, while Ford’s GDI engines were moderately turbocharged. Both of these suggested that GDI somehow increases an engine’s detonation margin and that GDI gives the designer leeway that can be used to advantage in more than one way.
With either carburetors or conventional port fuel injection, fuel is put into the engine’s intake air stream before it enters the cylinders. There, some of it evaporates promptly, some is swept along as still-evaporating droplets, while some creeps along the walls of the intake plumbing. Liquid fuel is very effective at taking up heat from manifold surfaces, so this adds heat to the air charge. At the same time, fuel is evaporating, which takes heat away from the air charge. When heat added is greater than heat taken away, that condition is called “mixture superheat,” and it reduces power by expanding the intake charge. This reduces its density so that it takes less of it to fill the cylinder. The end result is lower torque.
In addition, the evaporated fuel takes up room in the intake system, because it has become a vapor. This leaves less room for the air charge, which again is reduced in volume, causing a drop in torque.
GDI, by admitting only air to the cylinders, delivers a cooler charge because air—a good insulator—is less effective at picking up heat from the duct walls than is a mixture of air, fuel vapor and liquid fuel. The cooler the charge, the farther from detonation the combustion event will be. This increase in detonation margin allows us to either safely raise the compression ratio (notice that the Motus V-Four has a substantial 11.5:1 compression ratio) or to do what Ford has done and employ light turbocharging. Either way, torque and power are increased.
Why has it taken so long for GDI to become a design option? The answers are technology and need. Yes, the Mercedes 300SL sports car of the 1950s had direct injection, and so did many Allied and German aircraft engines of WW II. But those engines employed Diesel-style fuel-injection pumps requiring ultra-precision manufacturing that added about 30 percent to building cost.
Engines such as the Cadillac CTS and the new Motus V-Four use special high-speed digital fuel injection, based in part on the fine-particle-size injectors developed for two-stroke direct injection. This type of injection is a recent development. Conventional injectors of the kind used in port injection produce droplet sizes too large to evaporate in the shorter time available to direct injection, so a special injector is required.
In the 1950s the 300SL was interesting but there were no CAFE rules driving design toward lightness and improved fuel consumption, as there are today. And so auto makers just made engines as big as needed to move big automobiles—no need for sophistication.Today, a smaller engine means a lighter vehicle and less regulatory trouble all around, so GDI is catching on quickly. For the Motus motorcycle, designed as it is to deliver the torque of a V-Twin with the smoothness of a multi-cylinder, GDI was icing on the cake—a way to pack even more torque into the 100-inch V-Four.
Where are the multiple overhead cams and four valves per cylinder we’re accustomed to seeing on motorcycle engines? The Motus’s natural competitor, Honda’s VFR1200F, certainly has them. But there’s more than one path to the same goal of strong, smooth torque. Motus has used the money that could have bought extra cams and valves on sophisticated GDI. And it’s Motus’s 100 GDI cubic inches and two valves per cylinder versus Honda’s 73 cubes and extra parts. When we ride them both we’ll tell you the outcome.
This liquid-cooled engine is mounted longitudinally in the chassis, driving a conventional multi-plate motorcycle clutch and six-speed gearbox through bevel rather than spur primary gears. The engine is narrow—it’s 18-inches across. And it looks familiar to any American mechanic because it’s laid out just like an American car V-Eight. There are right and left rocker covers with the single camshaft in the Vee. The water pump is integrated into the timing cover casting.
The design choices Motus made tell us this is a Sport-tourer, capital “S,” small “t”. It has chain drive as every sportbike does. O-ring chain is reliable, light and strong. Motus gave this bike a modern six-speed transmission. It has a sportbike’s forged aluminum wheels from Marchesini—a 3.5- x 17-inch front and 6.0 x 17 rear. It has real brakes—not decorator substitutes that feel like a triple-X grip exerciser. These are 320mm discs and four piston monobloc calipers.
Wheelbase gives us another clue. When the emphasis is on “Tourer,” wheelbase grows to 60 inches or more. While grand for crossing Nebraska, this makes backroad carving difficult. Putting the emphasis on “Sport,” the Motus’s wheelbase is 57.5-inches. A 43mm inverted fork is set at 26 degrees of rake and 4.25 inches of trail—sporting but not extreme.
The four 86.5 x 70.0mm cylinders are targeted to make 140 horsepower at a moderate 7800 rpm, with torque peaking down at 4500. With that 11.5:1 compression that only a liquid-cooled engine can durably offer, that gives a wide usable curve that’s easy to ride for any purpose. The engine’s 90-degree design gives primary balance, while a pair of double-speed balancers zero out secondary shaking. Lubrication is wet-sump with screw-on filter.
The chassis is triangulated tubular steel, using the engine as a stressed member. A steel rectangular-beam swingarm completes the package. A composite fairing, 35-liter side bags, and an adjustable-height windscreen provide touring amenities.
The Motus spec sheet tells us this is a motorcycle for experienced riders who want a specifically American—and American-made—compromise between sport and tour. Its first engine run is coming up in a couple of weeks. We’ll stay tuned.
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