The recently developed SEEC-T (Subaru Exhaust Emission Control--Thermal and Thermodynamic Control ) system meets the 1977 emission standards of the United States including California and the 1976 standards of Japan without catalytic converters or thermal reactors and will satisfy the more stringent emission standards expected in the future. The SEEC-T system reduces HC, CO and NO/sub x/ 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. A description is given of 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 NO/sub x/ control on driveability, combustion stability and fuel economy; and (4) improvement in combustion by introductionmore » of secondary air.« less