They only flow 1300 if you flow them a 3.0 inches like 2bbls aree flowed. If you flow a 6pk at 1.5 like the 4bbls are then it will strugle to flow 1000 cfm, or about the same as a good T-quad and you are still stuck with a 6pk manifold, a simple adapter can fit a t-quad to just about any manifold.