The system changes the length of the intake funnel in order to maximize cylinder filling efficiency.
Normally the length of the intake funnel is a compromise. A long funnel is best for torque at low and mid rpm, and a short funnel is best for high rpm and maximum top power.
The YCC-I system makes it possible to use the high-rpm oriented system with the short funnel layout, while keeping the higher torque characteristics of the long funnel at low and mid rpm.
It was first launched on the 2007 R1 followed by the 2008 R6 and the 2009 VMAX.
The principle of variable intake length is based on the phenomenon of reflected pressure waves in the intake duct. They reflect at the end of the intake duct and return to the intake valve.
At low rpm the intake duct is therefore longer, creating a longer time for the pressure waves to travel. This longer time is needed because the period the intake valves are closed is longer too, and the reflected pressure waves should arrive at the intake valve when it is opening.
At high rpm the intake duct is shorter, because the time the valves are closed is shorter too. In this way the arrival of the reflected pressure waves is again matching with the opening of the valves.
