The final step is to have the valves and seats ground. There is an art to this as well. Knowing where to put the angles on the seat to streamline the flow past the valve. On the intakes, five-angle valve seats are common and four for exhaust. The valve heads will also have several angles. The base seat angle is important too, with 30-degree seats flowing better on the intakes than 45-degree. The basic shape of the valve is also used to increase flow. All this is somewhat specific to the particular head.