If "Dual Port" is the name for the Offy manifolds that had a split intake runner system, with a smaller cross-sectional runner for the primary barrels and a bigger cross-sectional runner for the secondaries, I have had a litttle experience.
I put one on a Buick V6 that I transplanted into a Porsche a long time ago. IMHO, that style of manifold is a neat idea that has no place on an FE meant to make power.
Not only does the divider occupy cross-sectional area that would be otherwise usable, it also brings quite a bit more flow losses due to all that surface area.
If you care about part-throttle snap, use a proper intake manifold and put a vacuum advance canister on your distributor.
Chris Weisberg
Carroll Shelby Enterprises
(310) 538-2914
4-cyl Offy Dual Port manifold:
