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Thanks, Christ! That was a pretty good description of how ported speakers work. So I'll take some time to think on that helpful analogy and maybe revisit it later.
Meanwhile, though I think I get how the intake acoustics contribute to power, and I see the reasonableness of the argument that "more power with the same amount of fuel equals the same power with less fuel", I get stuck on a counter-argument: If you're getting your power increase by cramming more air in, then you're also cramming more fuel in. So your power-per-unit-fuel efficiency should be the same.
But it's starting to make sense now. This is how I'm explaining it to myself:
The air does double-duty in driving the engine -- 1. chemistry for combustion, and 2. mechanical compliance (spring action). Assuming the same volumes of air, and therefore the same fuel usage, the spring action is the variable that can either add free torque if the intake resonance is in phase with the combust cycle, or subtract torque if it's out of phase. So by tuning your intake to your preferred RPM, you can get free torque on the same amount of fuel.
I guess what was throwing me was the idea of ramming more air into the cylinder, which if I'm understanding right, is a misinterpretation. You're really pressurizing the same mass of air, ie. less volume, not more. So since stoich is mass-to-mass, you use the same amount of fuel to get the torque-bonus (or torque-loss, as the case may be).
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