Why is ther no formula to figure out port volume?

So if I understand you correctly Moper, that if I give you a rpm that I will call peak rpm's say 6,000 that it will show something different for say 3,000 or 4,000 rpm's? How is the port volume going to change by rpm's, unless your looking at a max rpm's. So if this is correct then a 130 cc port runner for a given engine say a 318 that turns 6,000 rpm's won't be able to use a 150 cc port because the port will be too large.

I think that what he's looking for is what a given engine needs to have for so to speak the perfect port volume. I think that what your saying is a given rpm will need a given amount of air flow, this doesn't mean that the port volume will change but the airflow will. I guess I should put it this way, if we have 2 heads and one flows 280 cfm's @ .600 and the other flows 240 cfm's @ .600 then the one with 280 cfm's will make more power with both being the same port cc's. It will also have more port velocity because it's moving more air through a given size port or volume. With both having the same size valves. If both heads have different size valves then the port velocity will change due to the amount of area of the valves. But this will also be seen in the amount of port flow in the low lift ranges from .100 to .400 lifts. The smaller valves will generally flow more at low lifts than a larger one, but the larger one will flow more peak at a higher lift something like .700 or .800 lift. Correct.