because a well ported big duke will flow more then that, ..
BUT, it's not all just flow, .. the raised runner of the big duke allows
better delivery to the valve, better fuel delivery into the chamber, .
and well ported will flow well over 500 cfm.
typically a spread port head like the big duke will make at least 60 hp
more then a conventional head, ..
other consideration is average power not just peak, .. average power is
what really makes et and fast cars on the track, not just peak power.
Curtis