About the effect of WAI. Beside of the already mentioned reasons I can think of two others why it should work:
- fuel evaporates better when mixed with the warm air=> better efficiency=> lower fuel consumption
- the engine warms up a bit quicker when warm air is 'inhaled' (but this effect will be very very marginal I admit).
The gears can help in town depending on your situation. I plan on going from 3.55 to 3.92 in my truck to help with the city mileage because of where my OD/lockup point happens to be in relation to the local speed limits. Currently I can get it to lockup above 42 no problem and it can go as low as 38 if I REALLY watch to make sure the TPS doesn't click over to idle since locked in overdrive at that speed is about 1025rpm.
If I go to the 3.92 gears I can hold overdrive down to 35mph which means instead of climbing 4 miles of road home speeding 7mph over to hit lockup I can stay only a mph or two above the speed limit to get home in it. There are also a few 40mph roads I normally use where traffic hangs just under the 40mph speed limit so I get to cruise 37mph getting 13-15 mpg instead of 42 mph getting 18-21.
I have tried windows up - A/C off and it does not make a noticeable difference in mileage. My theory behind it is that on large V-8's the a/c pulls a small % of the total engine output. On smaller engines the A/C is taking a larger % of total engine output.
Currently I have a "passive" warm air intake like you described. I took the lid off the air cleaner box, and I covered the original air intake from the fender with duct tape. This forces the engine to take warmer air from the engine bay, but its still not as hot as I'd like it to be. My intake air temperatures are running 10 - 20 degrees above ambient. I know I can do a lot better, but I've been lazy lately.
similar to what ive done will make your car run better but while wai is on try to not to give it as much load esp on a truck, like if you're going to be hauling a full trailer and full bed I would take off the warm air intake but otherwise wai like hes saying will do you good, Maybe it will respond well under load im really not sure to be honest.. some one needs to try this, ive read a dyno that hai under lower rpms producer less power but under higher rpms produce more power
Yeah, if I was towing or heavy hauling all I have to do is rip off the duct tape, and put the lid back on the air box. it can be switched back in less than a minute. I often drive with a full truck, but its generally not much weight, and I've never towed with it. I always buy vehicles with towing packages mainly for the upgraded brakes, suspension, transmission cooler, and oil cooler. Often the towing package may include an upgraded alternator as well.