In 1957, Bob updated the two-year-old Thunderbird, replacing the factory 292 with a new 312ci engine (introduced as a Thunderbird option in 1956) and upgrading from a 6-volt system to 12-volt.

FORD MOTOR CO. A 1957 Ford Thunderbird. The last of Ford Motor Co.'s two-seat Thunderbirds is built Dec. 13, 1957, as production shifts to the larger, second-generation, four-seat "Square Bird." ...