Oh come on x'ed Toluene and Xylene are already in gasoline as well as Benzene and a few other hydrocarbons. Higher concentrations of these hydrocarbons = Higher octane, to a point. No more or less noxious fumes than the MMT that the refineries put in already. Now if you're thinking of the nitro methane family, that's a different story... That exhaust will burn your eyes and lungs...