Length helps to maintain fuel air velocity to a point. The fuel air mixture can stay in motion after the valve closes if it has a place to go. Other wise it has to stop. Its easier to speed something up that has slowed a bit than to start something that has stopped.

I have no faith in human perfectability. I think that human exertion will have no appreciable effect upon humanity. Man is now only more active - not more happy - nor more wise, than he was 6000 years ago. Edgar Allan Poe