Chrysler did a good deal of engineering work on tuned intake runners in the 1950s. The basic theory was developed on 4-strokes but it also works on 2-strokes if you take into account the differences in duration of the intake cycle. When the intake valve opens, a negative pressure wave travels at the speed of sound toward the carb until it reaches the open end of the velocity stack. A sound wave will reverse it's sign and now becomes a positive pressure wave when it expands into an open space (the end of the stack). The positive pressure wave travels back toward the engine at the speed of sound and can give a mild supercharging effect if the wave returns just before the intake valve closes. Longer intake timing requires a longer manifold runner. Higher rpm boost requires a shorter runner. A few modern high performance cars have intake runners that adjust their length with engine rpm to optimize the torque/power increase across the entire rpm range of the engine.