ok im used to turbocharged 4cylinder engines and looking at flow #s around 300cfm @ .400 lift for a ported head.

Ive always heard that SBC 350 heads flowed good but when I went to patriot performance and looked at their ported race head flow #s im seeing 230cfm and a maximum of like 290cfm at crazy high lift from what im used to. Whats up with this??? Is the cfm a measure of total head flow, or single valve flow? Why would a little head with tiny valves outflow a huge head with massive valves?