Things I have found that need to be taken into account...
The vacuum gage has been found to be the best indicator I have of FE. With the ram air hose installed it was good for a solid 1 MPG. But when the warm air intake from the exhaust manifold is activated there can be NO ram effect.
At the speeds I drive to and from town (45MPH) the vacuum runs about 15 inches of mercury. That translates to 7.367311 PSI. It takes energy to create that, and anything I can do the help means greater economy.
One thought is to use the air from the radiator fan to help. It is already nice and toasty (but less than the temperature setting on the intake heater which I measured at 133 F), and the energy to run the fan has already been accounted for, so I figure it might give a slight boost. All I would have to do is reroute hoses.
Every other form of intake uses power, be it hood scoop, or electric blower. Turbos are a different thing all together, but do create a little back pressure, hence the need for big exhaust pipes.
random thought from reading above. Ram air to air/water intercooler(warmer really) to manifold. Would be useless at low speeds, but at higher speeds down the Interstates or highways, the ram air pressure should negate the drop across the a/w IC while still providing hotter air that's pressurized more than what the motor pumps. Does that make sense?
Yes, it does. I was hoping the cooling fan might give a little boost, and at speed the air would be forced through the radiator with a far greater area than the tiny amount going around the cowling. Insects and birds would be filtered out by the A/C condenser.