I think like anything else, the flow bench is a tool, and is only as good as the individual using the information. You should not benefit any more by pressurizing the air as far as information gathered from a flow bench, the viscosity of air does not change with pressure, it changes with temperature. So flow characteristics won’t change with pressure. The bench is a static condition which measures flow at static valve positions, this is one piece of the puzzle. Also consider that nothing gets sucked into an engine, positive atmospheric pressure pushes air into the NA engine through the displacement of air by the piston. The pumping losses happen from the back side of the piston displacing air, the combustion side is then filled by atmospheric pressure pushing the air in to the void left by the motion of the piston. It would be interesting to experiment, but I don’t see anything different other than pressure, which is not going to give any significant result over what a current bench can provide.
Pressurized or not, the bench cannot tell what will happen with regard to cam timing, valve motion, the combustion process, fuel distribution, and so on,… So my guess is the current bench is adequate for it’s purpose for turbo and NA engines. Maybe even more so for a turbo application, since you will likely get high differential pressure in an NA between the cylinder and the port, which means higher velocity and more susceptible to flow disturbances, no experience, just guessing.
