Low Profile Single Plane Intakes

From Summit's website probably verbatim from Offy,
Offenhauser Dual Port Intake Manifolds

"Offenhauser Dual Port intake manifolds feature completely separate runner systems for the primaries and secondaries for more power across the rpm range. At low-load, the primaries feed the air/fuel charge through the smaller bottom passages at near sonic speed, improving power and efficiency. When the secondaries open, their charge goes through the bigger, cooler upper passages. Then, in turn, it is rammed into the cylinders when it encounters the high-velocity mix from the primaries. The results are better fuel economy and a 15-30 percent power increase
across the entire rpm range."

That divider will probably cut down on flow. The velocity of the primary is a good idea for off idle to cruising speeds.