A Buick friend of mine two weekends ago in his 3500 lb boat with a NA 450 or so cid Nail head motor broke into the high 10s, while only spinning to 6500 rpm.
I ported these heads near 20 years ago now so I know exactly what they flow.
Where taking on average @28" 215 cfm on the Intake and between 150 and 162 cfm on the Exh side, the difference being 2 ports on each head having to deal with a head bolt boss.
If you should ever get a chance to look at one of these heads and the ports they have you would be pulling your Chin hairs in wonderment that they could even power a car into the 11s!
So it's not just about air flow, in these heads from the burn pattern and lack of any signs of fuel wash these darn Nail heads chambers combined with there strange Intake valve bowl shape are very good at making power with the air and fuel amounts that they do receive.
