I used acetone in my dragster fuel years ago, as I tried mixing about 50-50 gasoline and methanol. Acetone is a great binder for fuels that normally don't mix well, or at all.
It's a common ingredient in octane boosters.
On the down side, acetone is hell on syntheic rubber parts, like fuel line, Viton tipped float needles and the occasional o-ring.
The way it boosts your fuel mileage is that it lets the spark timing be advanced more. Cars these days have knock sensors that will retard your spark when they sense ping, thereby killing your mileage (and overall performance).
