A lot of power mods actually work well to improve mileage if you can keep your foot out of it. I'd recommend:
Decrease your top cruising speed by 10mph.
Electric fan.
Conical filter on your stock airtube.
62mm throttle body and spacer.
FireWire ignition kit from (Deleted to allow posting...)
If you've installed larger tires, regearing to match the new tire size will improve mileage. Narrower tires will also help.
Don't pay the $250-$300 that most retailers want for a 62mm throttle body, I frequently have them available for $95 each.
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Um, this will probably not make it past the censors, but, how in the world would a throttle body spacer help on a multiport fuel injected engine?
All of the ignition, etc...happens at the wrong place for a throttle body spacer to impact it, the way that it COULD on an old school engine (Like with a carburetor, etc...)
If the person never drives through water, a cone filter can be an option to reduce intake drag, but obviously, as the engine computer/mass air flow sensors, etc...are constantly adjusting the fuel delivery to match the airflow, I would think increasing the airflow would onlyy be helpful in increasing mpg if the oem set-up just could not allow enough air in at cruising (MPG territory...) speeds...which, is unlikely.
If the rig has an offroad/water crossing possibility...then an open element air filter is often asking for trouble...as it can suck in water much more easily, etc.
The electric fan option CAN work, but, the alternator drag is increased, so the parasitic losses reduced by removing the mechanical fans is offset by the parasitic losses due to the increased alternator drag...
I found on swaps that the mpg DID improve overall with the e fan swaps, but not as much as hoped, due to the alternator losses...IE: At higher speeds, the e fan wins (Alt is declutched, airflow through radiator is sufficient from the speed alone, etc)...at lower speeds, the mech fan wins. I go e fan mostly so I can turn it off on water crossings.
The ignition upgrades, again, are only going to work if the oem system was not completely burning the fuel...and even then, only by the remaining to be burned fuel's percentage...so, what % is being used/left for improvement...unburned hydrocarbons going out of the exhaust pipe/into cans, etc? - Well, that's the percentage left for improvement...some thing less than 1% for sure.
I think the above suggestions, as an overall pattern, would be more of a top power related mod path, than an mpg improvement related mod path.
Dropping the speed works wonders for mpg...dead on....due to our aerodynamics of a brick...etc.
I'd add -
Increase the tire pressure to reduce tire hysteresis/rolling resistance.
Swap in synthetic lubes for ALL lubed parts, it really drops the mechanical losses and heat build-up, the engine and the diffs being top priority.
Look at the horizon, drive with peripheral vision...notice traffic patterns as far ahead as possible, and adjust acceleration and braking, etc...to allow as smooth a transition as possible, IE: Don't find yourself accelerating because the guy in front is, and then braking - because the guy in front accelerated into a slower traffic pattern, and then had to brake, etc. (Yes, people cut into the 1 car length space if it opens...but, they are paying a premium for it....you are saving money by allowing them in under those circumstances, etc.)
(Saving gas requires patience...leave earlier, rather than driving faster, etc.)
