In 1977 General Motors significantly down-sized their full sized cars. The Cadillac Fleetwood Limousine rode on a 144.5" wheelbase and was powered by a 425 cubic inch (7.0 L) V8. This engine was basically a de bored version of the 472/500 (7.9 L/8.2 L) V8 of previous years. Compared with the 1976 Cadillac Fleetwood 75 which it replaced, the Cadillac Fleetwood Limousine had a wheelbase 7.0" shorter and weighed about 900 lb (340 kg) less.
The 425 cu in (7.0 L) engine, a reduced bore 472, was further debored for 1980-1981 to 368 cubic inches or 6.0 liters. For 1981, the 368 was provided with a modulated displacement system designed by Eaton Corporation, controlled by a digital computer, which locked off intake and exhaust valves to two or four of the eight cylinders, thus running effectively as a V6 or V4 under light load conditions where in third gear, and over 35 mph (56 km/h). This engine was called the "V8-6-4", and its electronics and sensors proved troublesome and, except for limousines, this engine was dropped after 1981. The engine's controls and sensors were a stretch for the computer power of the era.
Both the 425 and 368 are small-bore versions of the durable 472 (which was introduced in late 1967 for the '68 model year). The larger 500 had the 472's bore but a longer stroke. This engine family was the last Cadillac cast-iron engine, and the last 'big-block'.
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