Kinda depends. What kind of carb? Street or race?
He and I have been exchanging text about this.
He has an open plenum Torquer manifold on a basically stock engine with headers no converter. 1st
It is running a 650 double pumper mechanical secondary's....2nd
Bog city.
Needs a good dual plane and a 600 Vac secondary. He can play with the Vac spring and get fair performance.