The DFV is an internal combustion engine that was originally produced by Cosworth for Formula One motor racing. The name is an abbreviation of Double Four Valve, the engine being a V8 development of the earlier four-cylinder FVA, which had four valves per cylinder.

Its development in 1967 for Colin Chapman's Team Lotus was sponsored and funded by major American automotive manufacturer Ford. For many years it was the dominant engine in Formula One, with the whole engine program funded by Ford's European division, Ford Europe and engines badged as "Ford" for Formula One championship races. DFVs were widely available from the late 1960s to the mid 1980s and were used by every specialist team in F1 during this period with the exception of Ferrari, Alfa Romeo, Renault, BRM and Matra, who all designed, produced and ran their own engines. Variants of this engine were also used in other categories of racing, including CART, Formula 3000 and sports car racing.

The engine is a 90°, 2,993 cc V8 with a bore and stroke of 85.67 × 64.90 mm (3.373 × 2.555 in). It reliably produced over 400 bhp, specifically reaching 408 bhp at 9,000 rpm, and 270 ft⋅lbf (370 N⋅m) of torque at 7,000 rpm. By the end of its Formula 1 career, it achieved over 500 bhp, with a peak of 510 bhp at 11,200 rpm.

The 1983 DFY variant had an updated bore and stroke of 90.00 × 58.83 mm (3.543 × 2.316 in), maintaining a displacement of 2,993 cc. It produced 520–530 bhp at 11,000 rpm and 280 ft⋅lbf (380 N⋅m) of torque at 8,500 rpm.

In 1965, the Fédération Internationale de l'Automobile, that administered Formula One racing, agreed to raise the series' maximum engine capacity from 1.5 litres (92 cu in) to 3.0 litres (183 cu in) from 1966. Up until that point, Colin Chapman's successful Team Lotus cars had relied on power from fast revving Coventry Climax engines, but with the change in regulations Coventry Climax decided for business reasons not to develop a large capacity engine.

Chapman approached Keith Duckworth, previously a gearbox engineer at Lotus but now running his fledgling Cosworth company with Mike Costin, who commented that he could produce a competitive three-litre engine, given a development budget of £100,000.

Chapman approached the Ford Motor Company and David Brown of Aston Martin for funding, each without initial success. Chapman then approached Ford of Britain's public relations chief, former journalist Walter Hayes, with whom he had developed a close working relationship from the early 1960s. Since Hayes had joined Ford in 1962 the pair had previously collaborated in the production of the successful Lotus Cortina, introduced in 1963. Hayes arranged dinner for Chapman with Ford employee Harley Copp, a British-based American engineer who had backed and engineered Ford's successful entry into NASCAR in the 1950s. Hayes and Copp developed a business plan, which was backed by Ford UK's new chairman Stanley Gillen, and approved by Ford's Detroit head office as a two-part plan:

The project was revealed by Hayes in a PR launch in Detroit at the end of 1965, but the engine was not ready until the third race of the 1967 season, on the 4 June at Zandvoort. Its debut proved successful. Graham Hill, who was in the team at the specific request of Ford and Hayes, put his DFV-powered Lotus 49 on pole position by half a second and led for the first 10 laps but was then sidelined by a broken gear in the camshaft drive. Team-mate Jim Clark moved up through the field in his identical car and came home to win. However, this dominant performance belied a serious fault in the timing gear. Clark took three more wins that season, but reliability problems left him third in the Drivers' Championship, 10 points behind champion Denny Hulme. The progress of the engine was documented in a film produced by the Ford Motor Company's film section, entitled 9 Days in Summer.