The Porsche 904 is an automobile which was produced by Porsche in Germany in 1964 and 1965. It was officially called Porsche Carrera GTS due to the same naming rights problem that required renaming the Porsche 901 to Porsche 911.
After having retired from F1 at the end of the 1962 season, Porsche focused again on sportscars. The 904 debuted late in 1963, for the 1964 racing season, as a successor to the 718, which had been introduced in 1957. It was the first Porsche to use a fibreglass body, appearing more like specialist racing cars than the modified sports cars typical at the time, and was painted white. It was also the first Porsche to use a ladder chassis. While many German race cars had used unpainted aluminium bodies since the famous 1934 Silver Arrows, most 904s were painted silver, the modern German national racing color. The 904 marks also the beginning of a series of sportscars that culminated in the mighty 917.
Porsche designed the GTS variant first to compete in the FIA-GT class at various international racing events. The street-legal version debuted in 1964 in order to comply with Group 3 Appendix J homologation regulations requiring a certain number of road-going variants be sold by the factory. Both versions featured a fibreglass body which was bonded to its steel chassis for extra rigidity, and achieved a drag coefficient of 0.34. The 904's mid-engine layout was inherited from the 718, also known as the RSK (from the German term for racing, Rennsport), the factory's leading race car. One hundred had to be built to satisfy homologation requirements (which were met in April 1964), and while 106 were produced, at a list price of US$7245 (FOB Stuttgart), "orders far exceeded that requirement", and more than the six works and 100 customer cars could readily have been sold. Unusually for Porsche, the two-seater bodies were provided by contractors, which would later become standard practise among race car builders. Some four or five 904s were produced each day.
Riding on coil springs (and thus the first Porsche not to use trailing arm front and swingaxle rear suspension), with unequal-length A-arms in front. The wheelbase was 90.5 in (2,300 mm) (by contrast, the Corvair's was 108 in (2,700 mm)), track front and rear 51.7 in (1,310 mm), height 42 in (1,100 mm), and ground clearance of 4.7 in (120 mm) on 15 in (380 mm) wheels. Frontal area was only 14 sq ft (1.3 m2).
It was powered by a four-cam flat four-cylinder engine, "probably the most complex four-cylinder" ever. 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 46IDA3 three-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. By the time it was installed in the 904, it was the 1,966 cc (120 cu in) Type 587/3, with 3.62-by-2.91 in (92-by-74 mm) bore and stroke and 9.8:1 compression ratio, it produced 198 hp (148 kW). It drove a five-speed transmission and a standard 4.428:1 final drive, with available 4.605, 4.260, 3.636, and 3.362 ratios.
To satisfy demand, twenty 1965 models were produced, some featuring a variant of the 911's flat six. A very few cars were raced by the factory fitted with a flat eight-cylinder power plant derived from the 1962 804 F1 car, the 225 hp (168 kW) 1,962 cc (119.7 cu in) Type 771, which used 42 mm (1.7 in)-throat downdraft Webers. The Type 771s, however, suffered a "disturbing habit" of making their flywheels explode. The six- and eight-cylinder models were identified as 904/6 or 904/8.
Race-prepared four-cylinder 904s weighed in at approximately 1,443 pounds (655 kg), giving them the ability to accelerate to 60 mph (97 km/h) from a standstill in less than six seconds (using the standard rear gear, which would be typical at Sebring) and to reach a top speed of 160 mph (260 km/h) (with the 3.362 ratio). However, the 904's fibreglass body was made by spraying chopped fibreglass into a mold, the amount sprayed often varied in thickness over the shape of the car and as a result the weight of the various cars was somewhat inconsistent; some were heavier than others.
Due to the less weight issues of the first generation plastic body, the 904's successor, the 1966 906 or "Carrera 6", was developed with a tubular space frame covered with an unstressed, lighter fiberglass body.
Making an inauspicious debut at Sebring in 1964, where it suffered clutch trouble, "a four-cylinder 904 took an astounding first overall" at the Targa Florio. It went on to a third at the Nürburgring and a perfect finish at LeMans, all with all five starters finishing, placed in the top twelve overall, among many much more powerful cars. 904s showed remarkable durability; they "almost always" finished, 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. 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, Zandvoort, Canada, and the Paris 1000 Kilometer, in the process taking SCCA's C-Production and E-Sports Racing titles. In addition, it won rally events including the Tulip, Munich-Vienna-Budapest, Geneva, and "highly acclaimed" Alpine Rally. For 1965, results were "equally impressive", seeing wins at the Spanish, Rossfeld, Hellbronner, and Gaisburg rallys, as well as a class win in a gruelling Monte Carlo Rally which saw just 22 finishers in in the points, out of 237 starters. 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.
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