a flow bench shows a porter how much air the head can flow at different amounts of lift of the cam. the size of the port is very important because you need to find a equal medium for flow and keep velocity of the air. most honda heads require more than knife edging the runners and cleaning and smoothing the ports. a ported head won't flow crap without the right valve job. you also need to deshroud the valves to keep airflowing smoothly do some bowl work to help prevent detonation, and keep a eye on the approach angle to the valves. all of these things add up to the difference between a good ported head and a paper weight.