We have recently developed the SEEC-T (Subaru Exhaust Emission Control - Thermal and Thermodynamic Control) system that meets the 1977 emission standards of the United States including California and the 1976 standards of Japan without catalytic converters or thermal reactors, and which will satisfy the more stringent emission standards expected in the future. The SEEC-T system reduces HC, CO and NOx by the following three means. First;air fuel ratio is set leaner than stoichiometric by improvements in the carburetor. Combustion gas temperature is controlled by EGR and ignition timing control. Introduction of secondary air into the cylinder by backflow from the exhaust port improves combustion at light load driving. These means reduce the three emission components within the cylinder. Second;exhaust port liners inserted in a Siamese type exhaust port reduce HC and CO discharged from cylinders by holding the exhaust gas at higher temperatures. Third;insulated exhaust manifold helps to lower residual HC and CO. This paper describes the following four aspects of the SEEC-T System: (1)Structure of the SEEC-T system. (2)Suppression and reduction of HC and CO. (3)Effect of NOx control on driveability, combustion stability and fuel economy. (4)Improvement in combustion by introduction of secondary air.