Design of Aston Martin’s legendary DB4 engine commenced about 1955 when the Aston Martin Technical and Engineering Director in post at the time, John Wyer, was tasked with planning a new Aston Martin to replace the DB2 family of cars, now reaching the full maturity. This new model would also require the development of a new engine.
Engine development was entrusted to a promising young Polish engineer, Tadek Marek. For some time, a discussion ensued as to whether the future of the company would be best served through a continuance of a 3 litre sized engine, which would emphasise refinement, or whether to emphasise the sporting ambitions of Mr David Brown, the company owner, in his quest for a sports racing car that would win at Le Mans. That debate was quickly resolved and resulted in an outline decision of an engine of approximately 3.5 to 4.0 litre capacity, 6 cylinder in line with twin overhead camshafts, capable of powering a new Aston Martin grand touring car at speeds upto 150 mph. This would require an engine capable of developing approximately 250 bhp at the wheels
Right from the start, another debate ensued as to whether this engine should use a cast iron block, which was preferred for reasons of refinement, or to use aluminium. That debate was settled quickly when it was discovered that there was a national shortage of suitable iron foundries. This made the choice of aluminium irrevocable. With an eye to refinement, need for longevity and endurance, Tadek Marek planned from the outset to use a seven bearing crank of unusually generous dimensions and being aluminium, also continued use of wet liners. The cylinder head, also of aluminium, would be twin overhead camshafts, allowing use of fully hemispherical combustion chambers.
The DB4 engine was initially sized with an engine of 3.7 litres capacity with a bore and stroke of equal dimensions of 92 mm. It developed about 240 bhp with a torque of 240 lbs.ft, using twin SU carburettors.
In 1961, following the launch of the Aston Martin Lagonda Rapide, the engine capacity was raised to 4 litres by increasing bore size to 96 mm, and used down draught Solex carburettors, the intention being to maximise refinement. There was a reduction in power, but its general refinement was markedly improved and there was good low speed torque, all vital characteristics for a bespoke coachbuilt sports saloon for the rich and famous.