All other parts of the formula make sense, the blower/crank ratio, the blower CI, the engine CI, the atmospheric pressure, but what is the significance of the 25.58?
I have never seen this formula before but looks like units on 7/2.75 would cancel ( i don't know what these are) if so the 25.58 would be in psi. If that helps, probably not huh.
Actually my guess would be the pressure of air at the temp the gas burns at. You would look this up. If gas burns at 760 degrees F then that is what my thermo book gives for pressure of air at that temp.
This could be completely wrong though, someone correct me please if it is.