Quote:
Originally Posted by Dimman
This is under the condition of "When the coefficient of flow is unity."
What does that mean "coefficient of flow is unity"?
Is it something to do with pressure differentials or something?
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'Unity' is obscure math-speak for 1, and flow coefficient refers to the efficiency of the valves/head. So yeah, it's referring to pressure drop across the valves. What it means is that the equation is only true for constant density (zero pressure drop, isentropic efficiency of 1, etc).
The equation comes from the fact that the mass flow rate of the gasses exiting the cylinder must be equal to the mass flow rate entering the exhaust manifold (area*velocity*density must be constant). If the density within the cylinder is higher, the velocity in the runner will be proportionally higher as a result.