Ricardo PLC

Ricardo is a British firm that provides automotive parts and engineering, environmental and strategic consultancy services. Founded by Harry Ricardo, it is based at Shoreham-by-Sea, West Sussex.

Previously listed on the London Stock Exchange, the company was acquired by the Canadian consulting firm WSP Global in October 2025.

The company was founded by Harry Ricardo as Engine Patents Limited in February 1915. Later that same year, amid the First World War, the company helped develop a 600 brake horsepower (450 kW) piston engine for a flying boat. In spring 1916, it helped with the design of a device to manoeuvre 25 tonnes (28 tons) battle tanks into position aboard railway wagons. Later in 1916, the company designed a four-stroke crosshead-type engine, capable of producing 150 brake horsepower (110 kW), to power the Mark V tank; this engine emitted no visible smoke and thus made the tank less detectable by the enemy. In April 1917, the first engine was completed; quantity production was quickly established, permitting one hundred engines per week to be manufactured by the end of that year.

By 1919, the company had set up a laboratory at Shoreham by Sea. Around this time, the company's name was changed to Ricardo and Co. During the 1920s, it developed a side-valve engine, which minimised the clearance between the piston and cylinder head thereby achieving all the advantages of overhead-valve engines without the cost. This new type of engine, known as the turbulent head, was patented (following protracted legal action) in 1932.

During the late 1920s, Ricardo designed a six-cylinder diesel engine that was capable of producing 130 brake horsepower (97 kW); manufactured by AEC, it was quickly adopted to power buses serving London, as well as long distance coaches and lorries. This type of engine, branded as The Comet, was taken up by numerous European vehicle manufacturers, including Berliet and Citroën of France, MAN of Germany, and Fiat and Breda of Italy, among others.

In the 1930s, the company undertook work to convert a Kestrel V12 to diesel operation using single sleeve valve technology: Captain George Eyston used the new engine in the Flying Spray, which, at 159 miles per hour (256 km/h), broke the world diesel speed record at Bonneville in May 1936.

Also in the 1930s, Henry Tizard, Chairman of the Aeronautical Research Committee, who was a proponent of a high-powered "sprint" engine for fighter aircraft and who had foreseen the need for such a powerplant with the threat of German air power looming, encouraged Ricardo to develop what eventually became the Rolls-Royce Crecy engine. In 1931, Harry Ricardo gave a lecture to the Royal Society of Arts, in which he invited his audience to "accompany me inside the cylinder of a diesel engine", passionately describing the process of diesel combustion, in great detail. In 1938, the company developed the V-16 engine for the Alfa Romeo Tipo 162, a car with highly streamlined bodywork.

Ricardo's experience was drawn on for multiple initiatives during the Second World War; substantial research work was contracted to the firm. Specifically, Ricardo's involvement in the development of jet propulsion is believed to have been as early as 1940. In 1941, the company developed a relief valve, subsequently named "Barostat", which automatically reduced the pressure in the fuel lines as the aircraft gained altitude, thereby avoiding the risk of the engine overspeeding: the ground-breaking Gloster E.28/39 jet-powered aircraft, designed by Frank Whittle, used this device. Ricardo also assisted in the design of the combustion chambers and fuel control system of Whittle's jet engine.