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You might find that when comparing port flow for different valve sizes that it is convenient to use a ‘flow coefficient’. This is usually defined as the ratio of the flow rate of the port and valve and the flow rate of a straight tube of the same diameter as the valve seat.
The flow coefficient is calculated from the ratio of (the volume flow rate measured through the port and valve in m^3 s^-1) divided by (cross sectional area of the port at the valve in m^2 times the square root of (the pressure drop across the port and valve in Pa, or Nm^-2, times the density of the fluid in kg m^-3)). This is a bit hard without an equation editor!
So, a flow coefficient of 1 means that the port flows the same as a straight tube of the same diameter. In practice a value of 0.6 is pretty reasonable. A FF 1800 Zetec has an inlet flow coefficient of 0.62 at 11mm lift, for example.
Good luck.
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