[speed220mph]

Rick,
The reason they are using such a low pressure drop is the flow bench simply can't pump enough air at higher test pressures such as 10 or 28 inches with just the filter as the restriction. It's too low. A cylinder head with manifold and carburetor in between would be a different story.

And, yes, the filter would be similar to running at a higher elevation because ambient pressure, say 29.92 "Hg (14.7 psi) standard pressure, would exist outside the filter unless there is some ram effect. But a restriction causing a loss of pressure through the filter would naturally drop the pressure over the carb, much like would happen with an increase in elevation. But a restrictive inlet is worse. The exhaust system must expell the exhaust into the higher pressure atmosphere, reducing pumping efficiency and making a filter restriction worse than would higher elevation.

Another bad thing with an air inlet restriction and a float bowl that's vented directly to the atmophere: The air/fuel mixture enrichens--gets "fatter"--since the pressure on top of the fuel is higher than that over the carb inlet. Sort of a choke effect. There's more vacuum in the ventri(s) to draw in fuel and more pressure on top of the fuel to push it in. This is why final jetting should be done with all induction-system componnents in place. Don't you love fuel injection with O2 sensors, baro sensors and all that hi-tech stuff that compensates for you?