In 1922 Bamford & Martin company (that later became Aston Martin) produced cars to compete at the Brooklands racing circuit, for Grand Prix racing, and to set world speed and endurance records. Two works Team Cars with 16 valve twin cam engines were built for racing, a record car known as the Razor Blade was built, and a number of other cars were built for customers for racing. One of these customer cars, chassis number 1916, was later re-built as the AM Halford and then again as the Halford Special.
Major Halford built two engines for the car. Each had an aluminium block and crankcase with six steel liners, with rubber seals at their base. Bore and stroke were 63 mm and 80 mm giving 1.5 litres, the Grand Prix formula for 1926. The cylinder heads were cast iron with two camshafts, twelve inclined valves, and two 12 mm plugs per cylinder. Drawing on his aircraft design skills Frank Halford’s first design showed that he proposed to use an exhaust driven turbocharger, but this was unreliable in tests. This was probably the first turbocharged racing car until Renault developed the Alpine turbocharged car in 1968 that went on to become successful Grand Prix cars in the 1970s.
When it was first raced at Brooklands in the 1925 BARC in August, however, the car appeared with a two litre Roots-type supercharger mounted on the front of the crankshaft. The AM Halford first raced in 1925 with the first 95 bhp engine. The narrow Aston Martin radiator was too small and a wider and deeper radiator was fitted and the car was renamed more simply the Halford Special. The second engine had twin magnetos mounted behind the two overhead camshafts and developed 120 bhp and is now installed back in the Halford Special.
Frank Halford raced his car twice in 1925 and 12 times during 1926.The car was fitted with a Berk supercharger, manufactured by PressureVac Ltd., 18a North Parade, Bradford, Yorkshire. Halford then sold the car to Captain G. E. T. Eyston, who would later hold the Land Speed Record, to race during the 1927 season. Captain Eyston raced the Halford Special car three times at Brooklands and achieved fourth place in the Monthléry French Grand Prix in 1927.
In the 1930s the Halford Special was dismantled by its new owner, Viscount Ridley. The first engine was fitted into a Bugatti Type 35 and the second engine was modified to keep the twin magnetos dry and put into a speedboat that sank soon after and the engine spent two years at the bottom of a lake. The present owner of the Halford Special traced the original parts in the 1970s and re-assembled the Halford Special back to its original condition.