OK who's making these?

[Jakey]

Decreasing the runner size as it gets closer to the intake ports will increase the velocity because of mass continuity. You have the same amount of air coming into the runner so when the cross-sectional area is decreased, velocity increases. The velocity of the air traveling through the runner can be looked at as a ) with the maximum air velocity at the center of the runner. The velocity at the very edge of the plenum is zero and increases in a ) shape towards the middle and then decreases again as you approach the opposite side of the runner.