Speaking just for myself, I don't know of any formula although there could be one. I usually think about what I am going to do with the car. Strip? Street? Cruise? Show? Combo of some? How was the HP built? What camshaft are you using? Are there certain requirements of that camshaft such as headers, CR, stall speed if auto, close or wide ratio 4 speed, rear gear ratio? I think the situation is as individual as the car itself, although there are certain parameters that you will probably want to maintain. Just my opinion, Carmine.