For backyard porting, concentrate on ‘line of sight’ flow which means smoothing up the bends around the head bolt bosses. Knocking off the casting flash or roughness and doing some bowl blending also goes a long way in getting those flow numbers up. Minimize what is done on the short turn radius and especially on the lower ports as the flow speed suffers in that area if the short turn radius is ‘straightened’ out. The final finish of the ports still needs to have some texture and not be mirror smooth so that some ‘friction’ or turbulence can be maintained between the port wall and the flow; this will assist in keeping the fuel from dropping out of suspension.

With the iron heads, the notches are required to keep the intake valves from hitting the cylinders wall edges with any substantial lift at the valve. While the aluminum head valves have been relocated so that the intake valves will now free drop into the cylinders, the notches do still help the air flow in that area and especially when the valve lifts are increased beyond the mild performance stuff. When doing the notches, be sure that they are kept above where the top ring resides within the cylinder bore.