Variable Valve Timing on Motorcycle Engines
I'm sure that you all seen the VVT (or Variable Valve timing) stickers on the back of Toyota cars, but now that VVT is being used on motorcycles, we probably want to know what it means. Variable valve timing was developed by a Italian called Giovanni Torazza in the late 1960s when he was working for Fiat.Valve lift (the distance a valve opens), duration and timing are usually fixed, and this contains the engine: a cam profile giving good performance at high revs will have high lift and long duration to flow the maximum mix into the combustion chamber. But at low revs this won't be the optimum profile: too much mixture means unburned fuel and lower performance. Variable valve timing 'alters' the cam timing to allow good performance at a wider range of revs.Kawasaki's system, which we can find on the Kawasaki 1400GTR, was designed jointly with Japanese car-maker Mitsubishi and works by mounting a rotor with four oil-filled chambers over the end of the inlet cam on which a series of vanes are mounted.
A small pump, acting on instructions from the ECU and based on throttle position and revs, pressurizes the oil, filling the chambers and pushing the vanes forward (and therefore advancing the cams) 26 degree.
This alters the timing of the valve opening, and gives the engine the best of both worlds; both bottom and top-end performance.
The Kawasaki variable valve system is self-contained, needs no maintenance and doesn't change service duration. So it's no extra cost for owners. Of course not every motorcycle manufacturer uses the same technology as Kawasaki, but in the end the working would be similar.
