You are coming at this problem from your aeronautics background. I am attacking this problem using thermodynamics and engine controls experience. Call it a restrictor or throttle (which means narrowing or restriction), it still creates a pressure drop that I have to pump air across to get it to the exhaust. This means that I do more work to get the air that the engine needs for combustion, while decreasing the temperature ratio of the thermal cycle (lowering efficiency).
Higher vacuum in the intake manifold is all bad (think about the flow work to pump air through the engine from that pressure to the exhaust manifold pressure, without even considering the chemical and thermodynamic implications).
Helmholtz tuning could possibly help, but the required intake runner size to get enough air velocity to see any appreciable benefits from Helmholtz would give up way more power than I am willing to give up. If the intake runner can provide even 0.1 Mach at 2400 rpm and 45 kPA pressure drop, They would have a tiny cross-section and would be something like 5 feet long. On top of that Helmholtz would only help for a very limited speed range.
I really should have done a better job of explaining my goals for this plan, I want my cake and I want to eat it too. I want a 250+ Hp rotary that will still give 35 or even 40 mpg.
I wonder how those wheels do on the corners?
I really do sound like I am being unrealistic, but I have a Metro if I want to drive for cheap, I want the RX7 to get decent mileage to see if I can. I also want it to retain some semblance of pleasure to drive, otherwise I might as well drive the Metro.
These basically perform the same function as a spoiler and are a very good idea. I might look into this (I really couldn't care much less what the car looks like).