1956 Thunderbird. The Thunderbird was such a sales success, that few changes were made to the car for the 1956 model year. The most notable change was moving the spare tire to a continental-style rear bumper to make more storage room in the trunk. The exhaust tips were moved to the ends of the bumper, and air vents were added behind the front wheels to improve cabin ventilation. Drivers would find that the weight of the outside rear tire caused uncomfortable steering feel. Among the few other changes were a 12 volt electrical system, new paint colors, the addition of circular porthole windows were now standard in the fiberglass roof to improve rearward visibility, and a larger 312 CID Y-block V8 added. The new V8 was rated at 215 HP (when mated to a 3-speed manual transmission) or 225 HP (when mated to a Ford-O-Matic 3-speed automatic transmission). 15,631 units were sold, much of the slower sales attributed to the continental kit taking away from the car's sleek lines and adversely affecting handling.