Abstract
Isuzu 6HE1 naturally-aspirated (NA) and turbocharged with chargecooler (TC) engines have established a good reputation, not only in Japan, but all over the world, since Medium-Duty Truck "Forward" with 6H engines were introduced in 1990(1). Features of these engines are OHC valve mechanism for high volumetric efficiency and ladder frame structured Cylinder Block for high rigidity. Efforts have been made on following improvements for 6H-series engines to meet current social needs and high demands from the markets: - Meet 1994 Japanese emission regulation; - Achieve top level performance in medium-duty truck segment; - Drastic reduction of smoke, even under transient condition; - Improvement of startability and reduction of white smoke; - Improvement of reliability and durability; - Weight reduction. Following are results of our efforts to achieve these goals, mainly on improvements in combustion and displacement enlargement.