VVT variable valve timing... is "shifting" the timing (opening / closing) of the valves throughout the engine's rev range - cars have been doing it for years - one reason they got there first is crash testing and weight gain - and the fact cars always needed more torque to combat the weight of the vehicle and passengers
within reason the power characteristics of a piston engine are only related to when / how we open and close the inlet and exhaust valves.... so a generator has mild cam timing giving a wide flat boring power curve and will likely never need VVT. But the more power we want, the more you end up with valves open for ages, and with both inlet and exhaust vales open at the same time (valve overlap) - this kind of works on a race track as they don't have hills and traffic jams, and on a bike where we're are all mad and change gear like halfwits and low torque works as they weigh almost nothing...
bike's have really gone with VVT for emission control - but we also get the benefits of a more flexible / lazier engine (feeling like its a bigger capacity)
there are various ways to alter the timing - the BM bike shift cam effectively smashes the end of the cam along a bit so we get a different cam lobe opening the valves at different times / revs - by shifting the cams sideways
the 1250 was horrid with an obvious mess up to the power curve for those that understand how the right twist grip functions - the 1300 now staggers the change in valve timing between the two cyls to further mask the switch over points
