Kawasaki Brings Variable Valve Timing to the Mainstream with the Concours 14
By Alex Edge
When I last discussed variable valve timing and lift technology, I was writing about the future of sportbike engine development (see
http://www.zxforums.com/forums/showthread.php?t=321). It came as something of a surprise, then, when I heard the rumors that the first application of TRUE variable valve timing in a mass-produced motorcycle would be a sport-tourer - specifically,
Kawasaki's 2007 Concours 14.
It does make sense, however. For all its terrific top-end rush, the 1352cc inline four found in the 2006 ZX-14 does respond somewhat sluggishly in the lower rpm range, a problem that will only be exacerbated by the greater weight of the new Concours. For those of you who have been reading up on the ZX-14, you know that the soft low-end power can be remedied by removing the restrictive butterflies in the intake tract, but it is likely that this change would also increase the emissions below 7,000rpm (above which the butterflies are fully open).
For Kawasaki's engineers, using a variable valve timing system is a much more elegant solution. We don't know yet what form of variable timing will be used, but rumors suggest that rather than a two-valve/four-valve switchover (like Honda's Interceptor), it will be a true variable valve timing system. This will allow the Concours 14 to effectively use a smaller camshaft at lower RPM, which will boost low-end power and torque, while at the same time offering improved fuel economy and lower emissions.
I find it unlikely that the Concours motor will use a multiple-profile system (like Honda's VTEC automobiles), which would give a pronounced step in the power output at the change-over point. This could be a safety issue in such a powerful machine, as the jump in power might cause the rear wheel to break traction at an inopportune time. Instead, I suspect the Concours will feature a variable timing system that can advance or retard one or both of the camshafts by means of some sort of motor on the end of the cam. This would allow the cams to have less overlap at low RPM, which, as I said, will increase power and torque while reducing emissions and increasing fuel economy. At higher RPM, the cams can offer more overlap to sustain a healthy power curve.
Of course, it's much more complicated than that - most automobiles that use such systems also take into account throttle position and engine load (in addition to RPM) in selecting camshaft timing, which means the ECU can optimize for mileage under light-throttle, highway cruising conditions, and also optimize for power at heavy throttle openings.
As I said in my article about camshaft design, variable valve timing carries a host of benefits for any powerful motorcycle which is intended to be used over a broad RPM range (i.e. a STREETbike). The Concours 14 should show that it's usefulness extends beyond sportbikes to motorcycles of any type, and it's only a matter of time before other manufacturers follow in Kawasaki's footsteps.
Source: Motorcycle Daily
