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Air pollution problems in California required control of vehicle exhaust emissions. The early development of catalytic converters and direct flame afterburners led to relatively complex mechanisms with substantial added cost to the vehicle. An evaluation of the primary factors affecting exhaust emissions indicated the feasibility of control by engine modification alone. A series of engine modifications were subsequently developed which reduced the exhaust emissions to below the California standard of 275 ppm hydrocarbons and 1.5 percent carbon monoxide and are discussed in this paper.

The use of lead compounds, when added to gasolines to enhance their antiknock properties, has resulted in more efficient combustion in high-compression engines, but their use has also caused lead deposits in the combustion chamber. To assess how lead antiknock compounds in gasolines influence combustion chamber deposits and exhaust emission levels, an intensive state-of-the-art review has been made, and data submitted by 18 different companies have been analyzed. These studies ranged in scope from single-cylinder engine investigations to a 122-car consumer test program. Based on this review, it was concluded that cars operated on leaded gasolines have higher equilibrium hydrocarbon emissions than those operated on unleaded gasolines, and that mileage accumulation conditions exert a major influence on the magnitude of the hydrocarbon net lead effect. The presence of lead in gasoline has no effect on carbon monoxide emission levels.

For the 1970 model passenger cars and light trucks, the Federal and California exhaust emission standards were reduced to 2.2 grams per mile hydrocarbon and 23 grams per mile carbon monoxide. This represents a reduction of approximately 33%. This paper presents the development of the significant features of the Chrysler Cleaner Air System of exhaust emission control for 1970. Included in this development are modifications in the engine, carburetor, ignition system, and other related components. Through these modifications and by optimizing the calibration of the engine operating parameters, the new exhaust emission standards were successfully met.