starting in february 1983, the amc i4 theoretically replaced the gm iron duke 151 under eagle hoods as the standard engine, though the installation rate is unknown. the i6 was improved for better performance by increasing the compression ratio to 9.2 to 1 (from the previous 8.2 to 1), as well as a fuel feedback system, a knock sensor, and the cec; thus allowing the continuing use of regular-grade fuel.