Fig. 10.16
The head of the valve is the primary obstruction of air flow through the port. For Maximum efficiency the flow must form a tight cone around the complete circumference of the valve head. If the cone is upset in any way the volume of air flow through the port will drop dramatically. This is the reason why some heads with 1.94-inch intake valves will out flow a head with 2.02-inch intake valves, Bigger is not always better.