The new Hydra-Matic automatic transmission was introduced in 1956 Cadillacs. In addition, the V8 was bored out to 365 cubic inches and produced 285 horsepower in standard models and 305 horsepower in the Eldorado. 2 new body styles - Cadillac Series 62 Sedan DeVille four-door hardtop and the Eldorado Seville two-door hardtop helped Cadillac sales to soar to 154,631 cars, 10 percent than the previous model year.