changes to the standard (series 30) eagle lineup for 1981 were notable. the gm "iron duke" inline-four engine became standard equipment, as amc's i6 became optional. the four was only available with the manual transmission in the eagle sedans and wagons. the amc inline-six was redesigned to produce more low-end torque, as well as made smoother running, more economical, and required less maintenance. the engineering improvements to the venerable amc engine also reduced its weight by to , thus making it "the lightest in-line six in the domestic industry".