All-new styling brought Cadillac up to the minute in 1957, and the fins grew even bigger in 1958; the engine had grown too, now boasting 310 bhp in standard form. Appearing bulkier and heavier than last year, the 1958 Cadillacs were not greatly changed engineering-wise, but were vastly updated outside. In typical fifties fashion, they were given an annual facelift, complete with the new quad headlamp setup now appearing on nearly every make in the industry.
The new bumpers were a little more traditional with the rubber tipped bumper guards toned down slightly and set lower against the parking lamps, which now occupied a single pod in the bumper below. The grille was stretched to nearly full car width, and was made up of dozens of round points, looking something like free-floating cleats. It was a unique and pleasant looking design that still said "Cadillac." One new model in the line was an extended deck Series 62 4-Door Hardtop, featuring an additional 8.5 inches in length added to the trunk area.
Bodyside ornamentation included a new simulated air intake now mounted on the front fender ahead of the wheel opening. Other changes included rocker panel moldings on all models, lower rear quarter panel stainless trim on Eldorado and Series 60 Special Fleetwood models, and a strip of stainless running from the headlight trim rings back to the midpoint of the car. The rear wheel opening fender skirts returned, but only on the Series 60 Special Fleetwood. Exclusive to this model and Eldorados were lower rear quarter panels covered in stainless steel, horizontally ribbed on the 60 Special. Interiors were more lavish than ever, with thickly padded seats and side panels, and the instrument panel continued its chrome laden horizontal theme.
Changes could be found under the hood in the form of a new "Tri-power" carburetor setup which replaced the space-robbing dual 4-barrel carburetor configuration previously used. The horsepower rating for the triple two-barrel carbureted engine was 335, very nearly reaching the "one horsepower per cubic inch" benchmark that all engineers strove to achieve. While this seemed like an unreachable goal a few years back, it should be noted that even within GM, this goal of "1 per 1" had been achieved at Chevrolet. It is interesting to note that with the additional bulk that Cadillacs carried, this year both Pontiac and Oldsmobile had larger displacement engines in their cars, which weighed less, although their rated horsepower was not allowed to be advertised as greater than Cadillac.
Last, but not least, the unofficial name of the Series 75 Fleetwood Imperial Sedan became the Series 75 Fleetwood Limousine. This was done to eliminate any possible confusion with Chrysler Corporation's Imperial division, established for the 1955 season.