weight dibasic ester and about 5 percent by weight propylene glycol mono n butyl ether the invention also relates to a composition for improving performance of an internal combustion engine in exemplary embodiments the composition can be a solid state material for example a tablet a powder or granules or granular material the composition can include an active ingredient that can include an iron containing composition and at least one synergistic carrier the iron containing compound can be ferric octoate ferric 2 ethylhexanoate ferric stearate ferric naphthenate ferric salicylate ferric carbonate diborylated ferrocene n butyl ferrocene 1 1 u2032 dimethyl ferrocene benzoyl ferrocene iron iii oxide fe2o3 iron ii iii oxide fe3o4 or combinations thereof the at least one synergistic carrier can be adamantane biphenyl also known as diphenyl phenylbenzene 1 1 u2032 biphenyl and lemonene naphthalene camphor camphene e 1 2 diphenylethene adamantanone acenaphthene or dicyclopentadiene preferred range of the active material e g ferrocene is about 1 100 by weight more preferred is about 4 25 by weight and most preferred is about 5 10 by weight preferred ingredient combinations for the composition are ferrocene and biphenyl more preferred are ferrocene and adamantane and most preferred are ferrocene and e 1 2 diphenylethene preferred are combinations of the actives are about 25 cerium containing compound and about 75 iron containing compound more.