For 1981, Cadillac began offering the V8-6-4 variable displacement variant of the 368 engine, which was designed to deactivate some cylinders when full power was not needed, helping meet GM's obligations under the government fuel economy ("CAFE") standards. Unfortunately, it did not work as planned, and sometimes did not work at all. It was a reduced bore version of the 1968 model-year 472, sharing that engine's stroke and also that of the model-year 1977–1979 425. The engine itself was extremely rugged and durable, but its complex electronics were the source of customer complaints.
Another problem with the 1981 model year was an unexplained balancing problem that affected the vehicle's overall handling. GM corrected this issue by installing a large, heavy steel plate under the driver's seat, a fact made popular by 1995's film Casino. The film's leading man Robert De Niro survives a bomb explosion, where the explosive had been attached to his 1981 Eldorado's undercarriage, on the driver's side, with that steel plate effectively shielding his driver seat from the blast beneath; the steel plate is credited with saving his life. The film, including the Eldorado explosion incident, is based upon Frank Rosenthal's life story.
Source: Wikipedia, 2012