Why is ther no formula to figure out port volume?

I was not a party to his flow info... however, my old neighbor (who does have his own personal SF600 bench runs a SS 351 Cleveland. It's making over 500hp. The biggest fix... weld in port reducers to lower the volume and help in the shape. These were taking out large amounts. Like 30ccs worth. Shape controls velocity, and as fast as the port can move cleanly is the goal.