Carb CFM recommendations

One thing that can’t be argued about is that 318willrun’s at home head porting is spot on. Anytime that an engine responds that dramatically to a larger than formulated cfm shows that the volumetric efficiency is well above what the formula calculates for. Usually 85% or so. The 750 is probably the actual optimal size, but it could be the “full blast effect” of the extra enrichment allowing air to start moving through the secondaries quicker.