[Fat Charlie]

So, added or reduced pressure upstream of the filter may not translate a change downstream of it, where the air actually gets sucked into the cylinders.

I know that most cars won't see any power benefits from homebuilt forced induction- I explain to customers that if the ECU isn't looking for additional air, slapping on a cold air intake on isn't going to get them any extra power even if they rig it with a leaf blower. Yes, sometimes I have to try a downsell. I was looking at it from the other direction: what if we blew unicorn farts into the air box and got the power that airflow math led us to hope we'd see? We'd drop our mpg. If I wanted that I'd have bought a different car.