"the length of the runner has a strong effect on the ammount of air that actually gets into the chamber during the intake valve cycle when the engine is not in boost. . . . Here, it is suffuicient to say that higher speed engines tend toward shorter intake runners. Low-speed and mid-range torque generally shows gains from longer runners. Turbo applications best results with long runners, which provide a braod flat torque curve at low speeds, while the turbo keeps the top end strong."
-corky Bell, p77-78