I've used Acetone ages ago in Holden 6's, mainly for better starting, they loved it. Up to about 5% is fine to use in a road car, and it does make a difference with the start.
Best use I've seen for Acetone was a 40/60 mix with Toluene powering Denzo's 300rwkw Pink Bits One-via drift car. Makes for big under-bonnet fires if it catches though..