This is a [variable-length intake][1]
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Variable-length intakes increase the pressure of the air entering the intake manifold thanks to a physical phenomenon called [Helmholtz resonance][2].

It's also known as *dynamic supercharging* since it avoids the use of a mechanical device (compressor/blower) to boost intake air pressure, which means the air enters the cylinders at a higher pressure. Needless to say:

    ▲ Air Pressure → ▲ Bang → ▲ Torque → ▲ Power

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How does it increase air pressure?
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Any air intake geometry has a certain Helmholtz frequency associated with it, just like how blowing over the neck of an open bottle produces a certain note or pitch.

At this frequency, the air molecules vibrate more, resulting in higher pressure.

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So why does varying the effective intake geometry help?
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Engine RPM will govern how often the intake valves open and shut. These valves generate pulses that translate to a frequency signature.

The idea behind varying the effective geometry is to get the Helmholtz frequency of the air intake to sync up with the frequency demanded by the engine over ***a range of RPMs***.

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This setup alters intake runner length
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*Much like how the Le Mans-winning [Mazda 787B did][3].*

The neat thing about this setup is its relative simplicity and robustness. Consider the 787B's trombone-like intake runners. The sliding motion between the two concentric pipes might be good in the short term, but I struggle to see how any mass-produced vehicle would feature this design; the interference between the two parts would require something special to last for an acceptable amount of time.

***Which is why the setup in this Yamaha is sheer genius***; it does away with the interference altogether while maintaining the benefits of the variable-length setup.

It's like an invisible, flexible wall. *Awesome engineering!*






  [1]: http://mechanics.stackexchange.com/questions/19608/how-do-variable-length-intake-manifolds-work?rq=1
  [2]: https://en.wikipedia.org/wiki/Helmholtz_resonance
  [3]: https://youtu.be/Go3Fgd1wgic?t=4m45s