Excellent article in Alkydigger web site about adding toluene to gasoline for more octane:
The Surfers top fuel dragster team in the ’60s was known to explore toluene with nitromethane for their racing fuel.
However different fuel mixtures, especially those with nitromethane, are touchy. They should be avoided without expert consultation!
The Alkydigger article indicates toluene has limitations as well.