In 1971, the LS-5 produced and , and the LS-6 option came in at and . In 1972, only the LS-5 remained, when SAE net power ratings and the move towards emission compliance resulted in a temporary output decline, due to lowered compression, to about and . The 1973 LS-4 produced and , with and gone the following year. Hardened valve seats further increased reliability and helped allow these engines to last much longer than the earlier versions, even without the protection previously provided by leaded fuel. 1974 was the last year of the 454 in the Corvette, although the Chevelle offered it in the first half of the 1975 model year. It was also available in the full size Impala/Caprice through model year 1976.