 While the 1953 and 1954 models were heavily reworked versions of the 1949-52 Chieftain models, they were engineered for the V8 engine that was supposed to be introduced on the 1953 models, but Buick division complained to corporate that the introduction might take sales away because Buick was introducing its new nailhead V-8 in 1953.The corporation held Pontiac back until 1955.Completely new bodies and chassis were introduced for 1955.