Did any of you horsepower calculator guys ever use this

PRH said
For every hp you need 1.4cfm?

1.4cfm relative to what?

At what depression?

Total air flow through the motor?

Per cylinder?

Per 8 cylinders?

I’m not seeing how that fits in with my dyno data.

The 1.4 rule of thumb says your 694 hp 589 cid it should peak hp at 5700 rpm is that close ?