[Darrell Ratchner]

Chopper, I agree with Pete. The 450's have very small venturi bores, which are really crowded by the booster venturis. This results in a high velocity air flow and a very strong signal to iniate the flow of fuel to the secondaries. I think it also helps because the primaries are opened 2/3 of the way before the secondaries open. Engine RPM is higher. I haven't checked it but it is possible that the accelerator pumps have a very slow opening and long duration which could overlap into the opening of the secondaries. Of course this would not mix immediately with the air in the secondaries but would probably help by the time the air gets into the cylinder.
Another interesting thing is the dual plane design of the Ford 2 x4 intake. Each barrel of the carb has a short and long path to take. The short path to a cylinder under the carb and a longer path to a different cylinder. If I remember correctly when all 8 barrels are open each cylinder can pull air from 4 different barrels, 1 primary on the front carb, 1 secondary on the front carb, 1 primary on the rear carb and 1 secondary on the rear carb. You really have to look at the manifold without any carbs on it and try to follow the air flow path.

One word of caution, Some of the Holley tech guys are not that sharp. Most are, but I have found a few that were really confused.