High Quality Content by WIKIPEDIA articles! The sixth generation Ford Thunderbird debuted in the fall of 1971. These were the biggest Thunderbirds produced, sharing a common platform with the Lincoln Continental Mark IV. They rode on a 120.4-inch (3,058 mm) wheelbase, measured 225 inches (5,715 mm) overall by 1976. Prices rose also, with the 1976 Thunderbird listing at $7,790 without options. They used a massive 429 cu in (7.0 L) engine that was standard in 1972 and 1973 or the optional 460 cu in (7.5 L) V8 engine, which was made standard for 1974 through 1976. These cars weighed around 5,000 pounds (2,268 kg). Due to their enormous proportions and large engines gas mileage was abysmal. These cars averaged anywhere from 8 mpg-US (29 L/100 km; 9.6 mpg-imp) to 12 mpg-US (20 L/100 km; 14 mpg-imp) depending on driving conditions. With the 1973 oil crisis taking its toll on the United States, automobiles were forced to downsize and become more efficient.