Offenhauser Dual Port intake manifolds feature completely separate runner systems for the primaries and secondaries for more power across the rpm range.

Primaries feed the fuel-air charge into smaller bottom passages at near sonic speed at the low end, which improves power and efficiency.

Their charge goes through the bigger, cooler upper passages when the secondaries open.  It is then forced into the cylinders when it encounters the high-velocity mix from the primaries.

These intake manifolds will result in a better fuel economy and give you a 15-30% power increase across the whole rpm range.

• 1965-75 Ford 240 Inline 6-Cylinder
• 1965-96 Ford 300 Inline 6-Cylinder