Road and Track - December 1979


The man behind it all was Texan Carroll Shelby. who had a long and successful career as a race driver behind him and had only quit because of a heart problem. Before his retirement. Shelby had tried to interest General Motors in a competition sports car, hut GM was interested only in Corvettes. so Shelby directed his immense charm and powers of persuasion in Ford's direction, with considerable success. What he actually did was to bring together Ford's engines (and Ford's money) with AC Cars Ltd in England, the builders of the AC Bristol.

In the best tradition of the British specialist car builder, AC Cars is nothing much more than a fabricating shop in the main street of a sleepy little English village called Thames Ditton. At the time, the Bristol Aeroplane Company had just stopped production of the engine used in the AC Bristol and Shelby felt that a small-block Ford V-8 would be ideal. He caused a modified but engineless AC to be flown to Los Angeles, where he and Dean Moon had it running within eight hours. The Cobra was born and Carroll Shelby was on his way.

Dan Gurney

The true ancestry of the Cobra goes hack as far as 1950, when a relatively unknown designer named John Tojeiro decided to offer a racing sports car chassis, which would accept almost any of the available competition engines of the time. Working by himself, Tojeiro built what was eventually to become the basic layout for the Cobra. One of his first customers was named Cliff Davis.

Davis ordered his car with a tuned version of the 6-cylinder Bristol engine. When it came time to body the car, Tojeiro was in a hurry and also somewhat lacking in resources, so he looked around to see what other people were doing. Showing excellent taste, he settled on the beautiful little barchetta body with which Carrozzeria Touring had clothed the Ferrari 166 Mille Miglia. and built a fair copy of it. although he simplified it along the way to suit the available amounts of time and resources. The TojeiroBristol became a famous and successful car and. thanks to Touring, it had an ageless appearance.

At the time, AC -Cars was having some bodies built by a company called Buckland Body Works Ltd, which was close to Tojeiro's shop, and Derek Hurlock. who is now the boss of AC, heard about Tojeiro while on a visit to Buckland. A deal was made and Tojeiro cooperated in adapting his design for road use and the car appeared as an AC, first with AC's own 6-cylinder engine and later with the Bristol.

Because it was built in a fabricating shop. the AC Cobra benefited enormously from its extreme simplicity. The chassis consisted of two 3.0-in. diameters steel tubes connected by crossmembers in ladder-style with spring towers at each end. Body framing and support brackets were welded to the main tubes and the bodies were of aluminum. Front and rear suspension was by transverse leaf springs and lower A-arms, and disc brakes were used all around. In the early stages of production, a number of modifications were made from time to time so that there was a certain amount of variation between the cars.

The first contract was for 100 cars, which were delivered between December 1962 and April 1963, and the first 75 of these were fitted with Ford's 260-cu-in. engine. However, Ford starting to build a 289-cu-in. engine which was absolutely ideal for Shelby's purpose. Ford had been doing extensive research into methods of thin wall casting, so the new engine was light. It had a rather extreme bore to stroke ratio of 4.00 in. to 2.87 in.,

which also helped to reduce the weight as well as keep down the piston speed and permit big valves to be used. and it was offered in a high-performance version giving 271 bhp. It was one of the best engines ever built.

The engine in Mike Shoen's car was, of course, tweaked by Shelby's men. but not excessively so. Shelby's sworn intention was to win with a team of Cobras the series of classic races which counted toward the international manufacturer's championship. a' to put it more succinctly in Carroll's words, "To git Ferrari's ass." These races included Le Mans, the Targa Florio. Sebring and other long-distance events, so stamina was just as important as speed. Fortunately, the engines were extremely rugged just as they came out of the box, so the stock crankshafts, rods and pistons were retained after being balanced.
The two engine men were Cecil Bowman and Jack Hoare and their primary job was very careful hand assembly to fine limits, and considerable attention to the gas flow through the heads. Four twin-choke, downdraft Webers were used and the diameter of both the intake and exhaust valves was increased by I /16 in. To take advantage of the larger valves, the ports were opened up and finally the complete combustion chambers were polished. Various compression ratios were used, but 11.6:1 was about normal. With these and other modifications, such as different valve overlap and ignition timing, the engine put out between 340 and 370 bhp. This output by no means stretched the engines anywhere near the limit, and Phil Hill recalls them as being very reliable as were the whole cars. Furthermore, according to Phil. the torque characteristics of the engines were such that you didn't have to bother very much where you were on the power curve.