A totalllly disagree with that entire statement.
500 cfm on a 318 is enuff to feed it well at all RPM's on a stock engine and do very well for mileage. The engine in a hopped up state has trouble sucking down 600-650 cfm's on the big end on the rpm scale and track.
Blanket statement on the next sentence. Stock heads also flow.
Polishing the ports after porting them is not the great idea of the century for a street car with limited Hwy. useage and mostly around town driving rather than a track only car.
OMG!!!!!!!!!!