Inliners International Forums General Discussion Hi Performance Harper intake for Chevy 6

With that manifold (and other of same design such as Nicson) you have to run all 3 as primaries.
The problem isn't how much gas (it never is) but how much air, and 1 primary for each pair of cylinders (not 3 primaries for all 6 cylinders) works OK.
The total CFM on this has to be pretty big - much bigger than a 3 × 1 McGurk or Offy.