Hunter, I would add a critical design feature of intake manifolds is length, shape and volume. The balance of air flow needs to be balanced between cylinders. Part of this is the length the air travels to each cylinder's intake valves. Part of this is the speed of the air flow as the open intake valve limits the time that air can flow. Faster air flow charges the cylinder with more air. Shape of the intake volume shapes the air charge including an turns or constriction points just before contacting the intake valves. Less turns and constrictions is good, more turns or sharper turns reduces the speed of the air charge just before entering the intake valves. Cylindrical intake runners are preferred to square. Smooth walls are preferred to rough castings, and mechanics often port and polish intake manifolds to reduce roughness and reduce sharp edges which reduce speed of the air charge.