The Porsche 904 achieved significant success, winning the 2-liter GT category in the Manufacturer's World Championship in 1964 and 1965, and it also won the prototype class in 1964.

The street-legal version debuted in 1964 in order to comply with group 3 appendix J[2] homologation regulations requiring a minimum of 100 road-going variants be sold by the factory.

[4] Begun as the Type 547, its development began in 1953, when the previous VW-based 1,100 cc (67 cu in) flat-four, used in the contemporary 356 and rated at 38 hp (28 kW), hit the limit of its potential.

[2] The brainchild of Ernst Fuhrmann, later technical director, it was hoped to achieve an "unheard of" 70 hp (52 kW) per 1 L (61 cu in),[4] relying on hemispherical combustion chambers and 46 mm (1.8 in)-throat 46IDA2 two-choke[6] Weber carburetors to generate 112 hp (84 kW) from the 1,500 cc (92 cu in) four-cam engine.

A complex design that proved "very taxing" to build and assemble,[4] but very durable, it was used in 34 different models, including 550 spyders, 356 Carreras, and F2/1s.

Unusually for Porsche, the two-seater bodies were provided by contractors, which would later become standard practice among race car builders.

From the coupé, the developers carried over the steel box frame and put on a light open plastic body.

[8] Modern day replicas of the 904 are currently being produced by a number of companies, including Martin and Walker[15] in the UK and Chuck Beck[16] and Dennis Frick at Europa Macchina in the US.

Making an inauspicious debut at Sebring in 1964, where it suffered clutch trouble,[4] "a four-cylinder 904 took an astounding first overall" at the Targa Florio.

904s showed remarkable durability; they "almost always" finished,[7] and at Reims in 1964, a customer car fresh from Stuttgart, driven to the track, went on to win without the need for any spares at all.

[3] For 1964, 904s racked up a 1–2 at the Targa Florio and class wins at Spa, Sebring (co-driven by Briggs Cunningham and Lake Underwood), the Nürburgring, Le Mans, Watkins Glen, Zandvoort, Canada, and the Paris 1000 Kilometer, in the process taking SCCA's C-Production and E-Sports Racing titles.

[7] In addition, 904s won their class at the Monza 1000 Kilometer, Targa, Spa, Daytona Continental, Le Mans, and Zandvoort, among others, repeating their E-Sports title win and adding an SCCA E-Production championship.