The way I see it, all the air would be at 14.6 psia but the velocity of the air would be higher. The only way the pressure would increase would be if something closed the system, and pushed the air forward while the other end was blocked. The air is not going to be compressed, there is no nozzle effect as the diameter of the pipe is constant, but the oxygen molecules will be there when you need them (intake stroke). In a carburated car, where air is drawn through the grille, through the radiator and into the air filter... It makes alot more sense to draw the air through the hood to keep temperatures low and velocities high. In a fuel injected car, the stock airbox is designed in the spirit of "ram air", in the form of a remote inlet.