"How much power potential can 350 cfm give? Well, that depends on a host of variables such as engine speed, overall induction system design, and piston speed. To put it in basic terms, the less restriction you have in the induction system and the more freedom you have to attain increased engine speeds, the easier it is to extract the full potential of the 350 cfm available. Most people don't know how much airflow their engine is actually asking for! This leads to builders wanting to purchase cylinder heads with way more airflow than their engines can possibly use. The end result is a low air-speed induction system that can't properly fill the cylinder by means of dynamic inertia and harmonic supercharging, which means the engine will never reach its full power potential.
"That said, a good cylinder head port design will flow a lot of air for its valve size. The bad news is that a bad port design will flow just as much if not more air! Airflow alone won't tell you if a port design will reach its power potential with 100 percent certainty. Everyone knows that it's easy to compare two 23-degree small-block Chevy heads with 220cc ports. Just pick the one with the most flow, right? That's about all the average builder can do, and in a lot of cases it's hit-and-miss. There are multitudes of ways to achieve that 220ccs. You can have a big pushrod pinch section and a very small bowl area, or a huge bowl area and a super small pushrod pinch area. One 220cc port can actually be choked off at the pushrod, short-turn radius, or throat area, hurting top end power. Another 220cc port design can have too small of a bowl area and too large of a choke and hurt power and torque equally across the entire power range. Having extra airflow isn't always bad, but it can't come at the expense of air speed. The ports must be sized properly. The amount of air Pro Comp Eliminator engines are asking for are exactly how much the heads flow, and that's not a coincidence. People want to make cylinder head design simple, but it's not. It's very complex and interdependent on a massive amount of variables."
Tony Mamo: "Having the most flow with the largest runner is certainly not always the best choice in cylinder heads. Perhaps a good rule of thumb or generalization is to choose the smallest head that flows enough air to meet your goals and properly feed your combination at the desired rpm range. Having more head than that will needlessly make the combination lazy and softer in the lower rpm while providing no appreciable benefit upstairs. A common issue I see a lot of is customers putting too large of a head on hydraulic roller combinations, which are typically limited to less rpm due to valvetrain control issues. A 210cc head on a 350 may work very well in a solid roller combination turning 7,500 rpm, but it's the wrong choice in a street car with a hydraulic roller valvetrain that limits usable rpm to 6,500 or so. A 195cc head would be a much better choice and would be a lot more crisp at lower rpm. It's all about choosing the right tool for the job.