In case anyone was interested in a graph of flow data for the B, C, and 03 4v heads I graphed the data from an article on mustangandfords.com that compares the three heads.
I would like to see that article.
This is showing b heads out-flowing non-03 c heads....hmmm.
I think the only big difference between the c heads was for better coolant flow.
Ford Four-Valve Head Information Guide - 5.0 Mustang & Super Fords
Here is the link to that article, the c heads are much different than the B heads in design. I know many performance shops and builders use B and 03 heads instead of the C heads.
As for the flow I think this quote might explain it, "A design downfall of C heads, and their larger (5.4 Navigator) cousins, is the relatively flat floor and utter lack of a short-turn radius in the throat of the intake port. As such, the incoming air tends to overshoot the valves, making the port "think" the valves are smaller than they actually are."
Ok...found this.
It is a velocity issue.
B heads vs. C heads
Post #3 na svt quote.
Smaller intake ports which equals higher velocity (resulting in more low end over B heads). The overall flow difference of the B and C port isn't that much (@28hg), but the gains are due to the better velocity and the a/f mixing. Oh, and the C heads use a better intake also. C heads will give you 20 or more hp at peak and more torque on the bottom end.