It so happens that Popular Hot Rodding Oct,, 2006 issue featured a long and detailed article on porting, written by David Vizard. That issue is still on the PHR site at:
http://www.popularhotrodding.com/tec..._head_porting/
I strongly suggest that anyone interested in airflow, port volume, or general head operation review the article, and especially on page 2 where David discusses port volume and effects on power production. He even has a dyno graph showing the very obvious differences in low and mid RPM power between a 200 cc port and a 171 cc port on a Chev 350. And his test numbers correlate very closely with what my car did when I changed from 165cc ports to 186 cc ports.
I would like to quote two sections of his article because it so closely mirrors what I have written in my book, and countless times on this board:
Quote 1 - "Although we are far from done with port shape, let's turn our attention to port size, or more accurately, port area, as this is about as important as shape. The phrase, "the ports have been opened up," is a no-no. Remember this first. The typical hot rodder's viewpoint that if some is good, more must be better (and too much must be just right) may be good when we are talking cubes, but it absolutely does not work when the subject is port area. Sure, a big hole must flow more than a small one, but when a valve is situated at one end (along with the rest of an engine's mechanical complexities) the whole deal that bigger must be better goes right down the drain. An engine relies far more heavily on ram filling of the cylinder and swirl generation than is often supposed. Ram filling is a function of mass x velocity squared (M x V2).
So yes, there is much more to head operation then sheer airflow, and especially peak airflow."
Quote 2 - Caption for the dyno results chart (double click it to enlarge) "FIG. 11-These tests, done on a 350 Chevy, show that though the bigger ports flowed about 5 cfm more at .5-inch lift, the smaller, higher-velocity ports produced a much better power curve. At 2,250 rpm, the smaller ports were up by 30 lb-ft. An engine equipped with the bigger ports would need about 25 cubes more to match the low-speed output of the smaller-port heads."
End of quotes from Vizard's article.
And be sure and look at the dyno chart for actual measured results - again simply click on the smallish chart for a large and detailed graph.
Jim Hand