The 904's mid-engine layout was inherited from the 718, also known as the RSK (Rennsport = racing, kurz = short), the factory's leading race car. It was powered by the 1,966 cc (120 cu in) Type 587/3, four-cam flat four-cylinder engine producing 198 hp (148 kW), "probably the most complex four-cylinder" ever. It drove a five-speedtransmission with a standard 4.428:1 final drive, with available 4.605, 4.260, 3.636, and 3.362 ratios.
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. Porsche realized it needed something all-new. The brainchild of Dr. Ernst Fuhrmann, later Technical Director, it was hoped to achieve an "unheard of" 70 hp (52 kW) per 1 l (61 cu in), relying on hemispherical combustion chambers (what would be called hemi in the U.S.) and 46 mm (1.8 in)-throat 46IDA2 two-choke Weber carburetors to generate 112 hp (84 kW) from the 1,500 cc (92 cu in) four-cam engine. The 1.5 liter weighed 310 lb (140 kg) dry, eventually producing 180 hp (134 kW). A complex design that proved "very taxing" to build and assemble, but very durable, it was used in 34 different models, including 550 Spyders, 356 Carreras, and F2/1s.
Performance
- Drag Coefficient: 0.34
- 0-60 mph (97 km/h) : <6 seconds
- Top speed: 160 mph (260 km/h)
