Highest flowing sbm heads?

Engines are fundamentally air pumps. I know there are other factors at play. But, fundamentally, from a pure energy conversion standpoint, the ability of an engine to make power is directly correlated to it's ability to efficiently convert the energy of fuel to combustion. A gallon of gas has a certain amount of energy waiting to release. That gallon of gas requires a certain amount of oxygen to convert to energy. The RATE of burn is directly correlated to how fast you can deliver oxygen to the fuel.

BURN RATE=HORSEPOWER. And that is absolutely driven by airflow.

If you don't believe this then next time you fire up a charcoal grill, get out your blower and feed the fire with a blower. You will see. It's all about airflow.

You must move a certain amount of air to RAPIDLY convert fuel to energy, period.

You can play with compression, swirl, very good combustion chamber shapes, bore and stroke combinations, oil control, low tension rings etc. These are the small things. The big thing in the first place is still airflow.