| First, any flow number for a port is absolutley useless without the test pressure (dP) used to achieve said flowrate. The unwritten industry standard for cylinder head flow rates is 28 inches of H2O (inH2O) dP for both the intake and exhaust. Second, the flow of a port under boost is a "different story," as you say, when compared to a port exposed to plain atomospheric pressure... but the flow rate under boost certainly isn't a mystery if you've already tested the port. The flow rate of air through any port will increase or decrease proportional to the square root of dP. If a port was flowed at some test pressure other than 28 inH2O, the flow @ 28 inH2O can be calculated as follows: Flow@28dP = flow@Xdp * (28dP/XdP)^1/2 For example, if your port flowed 275 cfm at 25 inH2O, the same port would flow 291 cfm at 28 inH2O. This relation can easily be verified on any calibrated flowbench. And, the flow at any boost pressure can be calculated as long as you have a baseline measurement.
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