Sunbeam was an old and respected British car manufacturer with a luxury and sporting heritage. It had become part of the Rootes group in 1935 and shared parts and technology with other Rootes makes Hillman and Humber after that. The first Sunbeam sports car after WW II was the model 90 Mk IIA Alpine of 1953, a open 2-seater version of the stately model 90 saloon, named after the successful participation of Sunbeam in the Alpine rallies.
A much more modern and nimble Alpine was introduced in 1959. It was based on the chassis of the little and plain Hillman Husky and powered by the 1494 cc 4-cylinder overhead camshaft unit from the Sunbeam Rapier. It constituted direct opposition for the popular mass produced traditional British sports cars of that era like the MG A and Triumph TR 3. Main selling points of the new Alpine were more comfort, better built quality and a better ride than its competitors.
Over the years the Alpine was improved constantly, and major improvements were indicated by adding an increasing Mark (Mk) number to the model name. At the time of the Mk II Alpine (1960-1963) it became clear that the car lacked power compared to its main and bigger engined opposition, like the new Triumph TR 4
The Rootes engineers looked for an in-house solution for a larger engine but didn't find one. The available engines either didn't fit or were too heavy. Developing a new engine for the Alpine was also out of question as a result of the financial troubles of the Rootes concern caused mainly by labor strikes.
Around the same time Carroll Shelby introduced his AC Shelby Cobra to the press in the US. The US was an important market for the British 2-seater sports cars, the majority of the production was sold there and this was invariably so for the Sunbeam Alpine. The West Coast Manager for the Rootes Group in the US was Ian Garrad and he had looked rather envious upon all the attention Shelby was generating with the Cobra. His opinion was that the more technically advanced Alpine could do better when fitted with a powerful V8.
Garrad examined a number of options for American V8 power to fit the Alpine, but most engines were just too big. That left either the small block Chevrolet engine or the 260 ci Ford unit Shelby had used in his Cobra. Since General Motors had no intention to supply engines to what possibly could become competition to their Chevrolet Corvette sports car, a model conceived to cut in to the popularity of the imported 2-seaters, using the Ford unit was really the only viable option.
Obviously Carroll Shelby was the man with most experience in successfully fitting the Ford V8 into a small British sports car, so Garrad and John Panks, director of Rootes Group America, were practical and consulted him. But to be on the safe side they also contacted US racing driver and engineer Ken Miles, a friend of Shelby and of British origin. Both agreed that fitting the Ford 260 ci V8 in the Alpine was possible and both, independently, set out to built a prototype. Around May 1963, about a year after the introduction of the Cobra, both prototypes were ready for testing.
Miles had taken the straightforward and least costly approach and had fitted the V8 into the Alpine with just minor alterations to the car. It had taken just 800 US Dollars to built but unfortunately drove terribly and had lousy road holding.
Shelby and his chief mechanic Phil Remington had done a more extensive job. They had placed the engine more to the rear of the engine bay, which required remodelling the firewall. This way a better weight distribution was achieved. They also installed a Borg-Warner T-10 4-speed manual transmission and a Ford Galaxie rear axle with Salisbury rear drive, components more up to handling the increased power. Also the original recirculating ball steering was replaced by a rack and pinion system from MG, a revised cooling system was installed (a lesson learned from experience with the Cobra) and dual exhausts were added which ran through the frame rails. This prototype proved far more convincing and offered a much better drive thanks to its almost 50/50 weight distribution.
The Shelby prototype was selected for further development; Shelby and Miles now working together in testing and improving the car. The tests included high speed runs in the Mojave desert but also negotiating normal traffic conditions on freeways in California. After testing in the US had been concluded in the summer of 1963 the Alpine V8 prototype was shipped over to Great Britain. There it was tried by the main man of the Rootes Group: Lord William Rootes of Ramsbury. Though quite advanced in age Lord Rootes put the car firmly through its paces on a local highway and some winding roads and returned enthusiastic. The Alpine V8 was made an official factory project dubbed code-name "Thunderbolt".
For the development of the Alpine V8 prototype to a production car Jensen Motors of West Bromwich was contracted, a company which also manufactured a Chrysler V8 powered sports car under their own name: the Jensen CV8. Jensen undertook elaborate testing, especially concentrating on engine cooling, and by the summer of 1964 11 prototypes had been completed, all based on the most recent Alpine Mk IV. One of the prototypes was exhibited at the New York Auto Show in the spring of 1964 and named the Sunbeam Tiger, after Henry Seagrave's Sunbeam V12 powered record car which had set the world land speed record in 1926. Though the visible differences with the small engined Alpine were limited (only wheel covers, striping, badges and of course the double exhausts indicated that it was a Tiger) the introduction was a success and orders started to come in. And so production began in the summer of 1964 of what we know now as the Sunbeam Tiger Mk I.