Honda is the world’s greatest proponent of the V4 engine configuration. Since 1982, the company has mass-produced various sport, cruiser, and sport-touring motorcycles powered by dohc 16-valve, liquid-cooled V4s in cylinder displacements ranging from 400 cc to 1.3 L.
Honda’s bike engineers like the V4 for its compact packaging, smooth power delivery, unique exhaust sound, and race-winning durability. Honda also has used the 800-cc VFR V4 to transfer its VTEC variable valvetrain technology from its automobile group to the motorcycle side.
Clearly Honda intends to keep the V4 as a core engine family showcasing the latest technologies for greater fuel efficiency, reduced emissions, and higher output. The next VFR will debut as a 2010 model, and it is so important to Honda that the company spent much of this year strategically using the Internet to release information about the innovative new V4 engine and an optional dual-clutch transmission (DCT).
Honda will deploy the DCT first in the VFR and later in other touring-model motorcycle ranges.
In late summer, patent drawings of the new 1.2-L (actually 1,237-cc) V4’s crankshaft and crankcase assembly surfaced on various enthusiast websites. These were followed by factory cutaway photographs of the VFR’s DCT—the first use of dual-clutch transmission technology in a production motorcycle.
And recently, Tsutomo Iishi, the VFR1200F’s program’s lead engineer, appeared on YouTube in a company-produced video interview, where he explains key highlights of the V4. Such “viral” marketing techniques and “unofficial-yet-official” leaks by Honda are in the vanguard of how OEMs are introducing new products and technologies to a global audience. Engineers, take note.
Iishi-san spent much of this decade on Honda’s MotoGP development team working on the RC211V, the company’s 990-cc V5 race engine, followed by the 800-cc RC212V, a V4. His experience with these engine types helped influence key design bogeys of the production VFR1200, he explained in the video interview.
“We didn’t go for top-end speed and peak top-end performance in the design of this engine,” he said. Instead, a linear power delivery, greater overall efficiency, and the engine’s exhaust tone were major design bogeys.
The V4’s compact, forged steel crankshaft offsets its connecting rod journals by 28°. The front cylinders (No. 1 and 4) are spaced wider apart than the rear cylinders No. 2 and 3. This configuration helps make the rear half of the engine much narrower than the front, thus slimming the center of the motorcycle and providing more legroom for the rider in this critical area.
The Honda video illustrates how the new VFR’s front cylinder bank, though wider than the rear, is still narrower than the single bank of Honda’s current CBR1000 inline-four—quite a packaging feat.
The crankshaft gives a 1-2-4-3 firing order. Honda calls this a "Symmetrically Coupled Phase-Shift Crankshaft" and combined with a 76° splay between the cylinder banks, the arrangement gives perfect primary balance. Its smooth running characteristics negate the need for a counter-rotating balance shaft.
Another clever engineering touch with packaging and operational benefits is the use of Honda’s Unicam sohc valvetrain on the front and rear cylinder heads. According to Iishi, this allowed engineers to reduce the size of the engine’s exhaust side, allowing the powerplant to fit a very compact chassis.
The Unicam was adopted from Honda’s proven CRF450 single-cylinder motocross engine. It uses a single camshaft to operate each head’s intake valves via direct-acting bucket type tappets, and long rocker arms to operate the exhaust valves.
Honda engineers claim the Unicam head is lighter than a dohc type. The arrangement also allows an ultraflat combustion chamber, which allows engineers to optimize the combustion process. Ignition timing is 104°-256°-104°-256°, a setup that helps create the V4’s unique exhaust note.
It was long rumored that the new VFR’s rear cylinder head would be a dohc type with four bucket-type tappets and fitted with a new iteration of the current VFR800’s Hyper-VTEC system. Honda had developed a cylinder-deactivation system allowing the engine to operate in two- or four-valve mode, depending on load, as well as being able to completely deactivate two cylinders.
This sophisticated, complex system would allow the 1.2-L V4 to effectively function as a 600-cc twin, providing up to 30% greater steady-state cruising efficiency. However, it was not implemented in the 2010 VFR.
Honda claims 90% of the V4’s peak torque is available at 4000 rpm. The engine’s redline is 10,200 rpm. The company has not yet released output figures.
Regarding the optional DCT, it is the latest in Honda’s wide-ranging R&D for new methods of transferring power in two-wheelers. As it does in cars, the dual-clutch gearbox provides precise, rapid, semi-automatic gear changing.
To provide maximum flexibility to the rider, the new DCT features three operating modes—two full-auto modes (D-mode for regular operation and S-mode for sporty riding), and a six-speed manual mode, which delivers the same shift feel as a manual transmission.
The new transmission was developed exclusively by Honda, which has scaled the transmission architecture for use with large-displacement V4 engines in the VFR and ST model ranges.
Bikes equipped with the standard 6-speed manual gearbox feature a slipper-type clutch, as typically fitted to road racing bikes. The slipper mechanism helps minimize the effect of deceleration torque on the drive wheel when the rider uses engine braking to slow the machine.
All VFRs feature shaft final drive for the first time, replacing chain drive. The new arrangement uses a constant-velocity universal joint to compensate for changes in driveline length due to rear suspension travel.
Watch for more details of the new Honda VFR1200F, its V4 engine, and DCT in upcoming issues of this publication.