Ok, at this point i think i've got enough information on this. So here's the set up and what my results are. Also, this won't be the most scientific thing you'll ever read, sorry.
First off, for those who want the quick answer, acetone really does not improve your fuel mileage...
1992, Ranger extended cab
4.0L OHV
M5OD-R1, 92 Rear Axle - 3.08:1
205/75R14 Tires
2WD
Ok, so I tried to keep my driving as consistent as I could, however, through the course of my testing i encountered traffic jams on the highways, really windy some days, sometimes morning, sometimes afternoon, mostly perpendicular to travel. Mostly highway commuting to work, 20% below 55, 30% 65 -70, 50% 70 - 80 mph. rough estimates, i did not count miles to get those percentages. I drove with the tailgate closed, and an empty bed.
While i tested my tanks, i gathered some information comparing acetone and gasoline. The myth about acetone having less surface tension and thus reduces the gasoline's surface tension in order to make it burn more completely is just false. acetone has a surface tension of 0.024 N/m, Gasoline's is 0.022 N/m.
In general, comparing any properties of the two considering the respective weight percents of the mixture. Any pro or con of the fuel mixture will only be negligible.
Keep in mind, the information i found on gasoline is rough estimate. Gasoline's have proprietary blends, so shell, conoco, excon, sinclair, BP will all have there different mixtures. Gasoline is basically mix of various hydrocarbon fuels. For the most part i used the same gas station every tank, but i'll be honest i don't even know what brand it is.
ok, so this is a comparision of the two fuels at a 400:1 ratio;
The density of Gasoline is about 46.176 lb/ft3 and Acetone is 49.30 lb/ft3. With a 400:1 ratio, the mixture should have a density of 46.18 lb/ft3, which isn't enough to make a difference on the A/F ratio.
Gasoline has a Heat of Combustion of 20.2 MJ/kg, while Acetone has 13.1 MJ/kg. The mixture should have an Energy Density of 20.1 MJ/kg. This would indicate that you would loss power and use more fuel, again though, negligibly.
Looking at the heat of vapor, Gasoline's is 330 BTU/lb while acetone's is 220 BTU/lb. Final mixture should have a Heat of Vapor of about 319.8 BTU.lb. Suggests the mixture would evaporate easier, it's still negligible.
Now, here's a look at my tanks;
1st) 895:1 mixture, 154.7 miles on 7.5 Gallons - 20.63 mpg.
2nd) 545:1 Mixture, 360.4 miles on 17.4 gallons - 20.7 mpg
3rd) 390:1 Mixture, 157.9 on 7.6 gallons - 20.8 mpg.
4th) 612:1 Mixture, 334.7 miles on 16.2 gallons - 20.7 mpg
5th) 2680:1 Mixture, 317.8 miles on 15 gallons - 21.2 mpg.
While no tanks are ever created equal, I tried to keep as smooth and fluid of a driving style as possible. I monitor throttle position with a vacuum gauge, and I flow with traffic. There's a lot of hills on my commute, both ways, so I hold the pedel and let my truck slow down up hill and speed up down hill. Elevation changes on my commute by 1200 ft.
It's a bit of a guessing game coming up with mixtures. Since I was adding acetone to the tanks before the gasoline so I could get good mixture, I had to predict how many Oz of acetone I would add to get a certain mixture. Add the gasoline, assuming the pump will always stop at the 21 gallon tank capacity, give or take. Then by knowing the amount of acetone you added, and assuming always 21 gallon total, give the final mixture approximation. From tank to tank i take how many gallons it should take to fill 21 gallons (projected from the gas gauge), calc the amount of acetone still in there, calc how many more Oz of acetone to add to make a final ratio, and then recalc based on how many gallons i actually had to add to fill the 21 gal.
Anyway, short story - long, there isn't any real noticeable improvement. With all the uncertainties that I was not able to account for, the results are negligible. I have noticed that my tank needle moves more uniformly. I think there may be a nice cleaning effect from the acetone as it is a great solvent for both polar and non-polar molecules. Before this, i generally keep my fuel system pretty clean as it is, Lucas injector lube about twice a month, fuel filter is 6 months old, injectors are 10 months old, new sparks, wires, air and oil filters.