Abstract: A method of operating a spark ignition internal combustion engine with unleaded gasoline is disclosed wherein methylcyclopentadienyl manganese tricarbonyl (MMT) is used as a primary antiknock compound and from about 5 to about 60 moles of benzoylacetone or methyl benzoylacetone per mole of manganese is used as a co-antiknock compound. These co-antiknock compounds are particularly suitable because they do not react with wet rusted steel in gasoline distribution systems, nor with terneplate surface coatings in automobile fuel storage tanks.

Abstract: Novel gasoline compositions comprising gasoline and dissolved or dispersed therein small quantities of from about 0.5 to about 100 parts by weight of a driveability-enhancing fluorine-containing polymer per million parts of gasoline will, after carburetion in a multicylinder automobile engine, plate out a fluoropolymeric deposit on the interior surfaces of the intake manifold of the engine thereby establishing on the manifold metal surface a coating of low wettability by any hydrocarbon gasoline component, either aliphatic or aromatic, and significantly improving the driveability performance of the engine. The driveability-enhancing fluorine-containing polymers useful in the gasoline compositions of the invention are characterized in that they must (1) have a critical surface tension of <17 dynes/centimeter at 25.degree. C, (2) have a high contact angle of at least 40.degree. to toluene at 22.degree.