When working on motors and using "theory" please remember the valves open and close interrupting the air flow on both intake and exhaust sides.
My message is a flow bench doesn't do that so make sure you have before and after data from either an engine or chassis dyno or from the track with very similar weather conditions when testing before and after ALL changes
I remember meeting Jacko, an early SO CA very good head porter, in 1969. He had some aluminum 426 hemi heads he was working on for Mopars Direct Connection parts R&D department, he didn't have a flow bench and said he could see what the air would do under vacuum or pressure on the exhaust side.
I'm sure he used a big commercial vacuum cleaner with a smoke tipped sparkler on the intake side and would reverse the hose on the vacuum hose to make pressure on the exhaust side.
i heard later that he would drag out one of the blocks he had to mount the heads on to do his testing from inside the cylinders with an adapter to seal against the cylinder walls
I was really lucky to be able to meet and get to talk to him for a short while, I was installing his phone service after he moved from the coast out to the desert