[40 Deluxe]

Air flows the best in a straight line. Anytime you force air to change direction, flow is reduced. So you want these changes to be as gradual and as smooth as possible. Thus the major air flow is out of the port and up against the head surface and then down into the cylinder, kind oaf a gradual arc. Relatively little air flows directly along the deck surface into the cylinder. Of course, in a high RPM race engine, you're after every last bit of flow, so you trade compression for better cylinder filling.