The fifth generation of the Chevrolet Impala is a line of full-size cars produced by Chevrolet from the 1971 to 1976 model years. The largest generation of the model line, the fifth-generation Impala grew to a 121.5-inch wheelbase (125 inches for station wagons) The Impala was offered as a four-door pillared sedan, four-door hardtop (sport sedan), two-door custom coupe (sharing its formal roofline with the Caprice), two-door sport coupe (semi-fastback roofline, shared with other B-body coupes), and two-door convertible. By the end of its production, the fifth-generation Impala had transitioned from a higher-trim version of the full-size Chevrolet sedan line to its base vehicle, as Chevrolet had ended sales of the Biscayne and Bel Air in the United States. For 1977, the Impala became the first primary sedan line of the Big Three automakers to undergo downsizing. History Overview The 1971 redesigned B-body would be the largest car ever offered by Chevrolet. All 1971 Chevrolet engines featured lower compression ratios to permit the use of regular leaded, low lead or unleaded gasoline of at least 91 octane rating per GM corporate mandate in anticipation of the catalytic converters planned for 1975 and later models which necessitated the use of unleaded fuel. A high-performance big block V8 was available in the form of the Turbo-Jet 454, which produced 365 hp in 1971, but power decreased as the years went along. The 1970s marked the impact of the 1973 energy crisis with gasoline prices doubling from 1973 through 1979 and industry car sales plummeted 20 percent between 1973 and 1974. For the first time in recent history, annual passenger car travel in the U.S. declined. The Impala's sales dropped to 176,376 units in 1975, the weakest since its introduction in 1958. An Econominder gauge package was offered for 1975 and 1976 models. 1971 1971 Impala models offered the same body styles as previous years. Newly standard features included power front disc brakes, inside hood release, and a revised Astro-Ventilation system that utilized air distribution grills in the trunklid. The new body featured a double panel roof for improved rollover protection and flush exterior door handles - both features previously introduced on the 1970½ Camaro. Engine offerings included the base 145-horsepower, 250 cubic-inch Turbo Thrift six-cylinder (available only on the Impala four-door sedan as well as the lower-line Biscayne and Bel Air sedans) and 245-horsepower 350 cubic-inch Turbo Fire V-8 (standard on Impala