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Tapered full radius bellmouths are similar but different to your velocity stacks. Yours are the semi radius, parallel type. The concept of the full radius is to improve the air speed entering the bellmouth [much like an aerofoil] and the tapered tube is yet another improvement in the ram effect of air entering the carb throat. Another point worth mentioning is that air typically enters the velocity stack in a doughnut shape, entering from the edge of the ram tubes rather than from the front, in the middle of the tube.

see pic for example.