Like many British specialist manufacturers, AC Cars had been using the Bristol straight-6 engine in its small-volume production, including its AC Ace two-seater roadster. This had a hand-built body with a steel tube frame and aluminium body panels that were made using English wheeling machines. The engine was a pre-World War II design by BMW which by the 1960s was considered dated. Bristol decided in 1961 to cease production of its engine and instead to use Chrysler 331 cu in (5.4 L) V8 engines. AC started using the 2.6 litre Ford Zephyr engine in its cars. In September 1961, American automotive designer Carroll Shelby wrote to AC asking if they would build him a car modified to accept a V8 engine. AC agreed, provided a suitable engine could be found. Shelby went to Chevrolet to see if the