Like many British specialist manufacturers, AC Cars had been using the smooth, refined Bristol straight-6 engine in its small-volume production, including its AC Ace 2-seater roadster. The engine was a pre-World War II design of BMW which by the 60s the company knew was considered dated. Bristol decided in 1961 to cease production of its engine and instead to use Chrysler 313cid (5.1 L) V8 engines. Although untrue, it is commonly believed that AC was left without a future source of power and that American ex-racing driver Carroll Shelby saved the company from bankruptcy. AC started using the 2.6 liter Ford Zephyr in all of its cars. Shelby, in September 1961 airmailed AC a letter asking them if they would build him a car modified to accept a V8 engine. Shelby had previous experience with Anglo-American hybrids, having raced an Allard. He first went to Chevrolet to see if they would provide him with engines, but not wanting to add competition to the Corvette they said no. Ford however, wanted a car that could compete with the Corvette and they happened to have a brand new thin wall small block engine which could be used in this endeavor.   An artists rendering of the first AC Cobra, with the 260in³ engine. Note the narrower track and smaller wheelarches with flattened lips.

 

AC agreed, provided a suitable engine could be found. It was, in the form of, Ford's 260 in³ HiPo (4.2 L) engine - a new lightweight, thin-wall cast small-block V8 tuned for high performance. In January 1962 mechanics at AC Cars in Thames Ditton, Surrey, England fitted the prototype chassis CSX2000 with a 221ci Ford V8. After testing and modification, the engine and transmission was taken out and the chassis was air freighted to Caroll Shelby in Los Angeles on February 2, 1962. Here it was fitted with an engine and transmission in less than eight hours and taken out on test. Carroll Shelby claims the name "Cobra" came to him in a dream.

 

 

Source: Wikipedia.