it gets hard to nail down cfm to hp relationships because it depends on what parts or circumstances you are talking about, 2hp/cfm is a general rule,, at 28".

on nhra stock eliminator cars its more of a gain because the heads flow so poorly, they are more restrictive to the displacement and accleration of the engine. they see more like 3-4hp per cfm.

also,, on an engine like a stroked small block or big block,, a 20 cfm gain will result in more of a power gain than on a std stroked or smaller engine due to the head being more restrictive to the larger engine.

jeff