Porsche 904 Carrera GTS: the fibreglass racer for the road

The Porsche 904 Carrera GTS is a GT sports car built in 1964 and 1965. It was street-legal, so it could be driven to the circuit as well as raced, and it was sold as the Carrera GTS rather than by its internal code 904. A hundred and six were built, and it took the two-litre GT class in the manufacturers’ world championship in both seasons.

Porsche 904 at a glance

History of the Porsche 904

After leaving Formula One at the end of 1962, Porsche returned to sports car racing. The 904 appeared late in 1963 for the 1964 season as the successor to the 718 of 1957, and it was designed to compete in the FIA GT class. Group 3 appendix J required at least 100 road-going cars to be sold, so Porsche built a street-legal version; a hundred and six were made at four or five a day, listed at US$7,245 FOB Stuttgart, and orders far exceeded the requirement.

The car was sold as the Carrera GTS, not as the 904: Peugeot held rights to three-digit names with a zero in the middle, which is why the 901 became the 911. The road-legal 906 that followed was sold as the Carrera 6 for the same reason, while the pure racing 907, 908 and 909 were not affected.

The mid-engine layout came from the 718 RSK. Power came from the 1,966 cc Type 587/3 four-cam flat-four with 180 hp, a development of the Fuhrmann engine that had begun as the Type 547 in 1953, when the 1,100 cc Volkswagen-based flat-four of the 356 reached its limit. It drove through a five-speed gearbox with a 4.428:1 final drive as standard, with 4.605, 4.260, 3.636 and 3.362 ratios available.

The 904 was the first Porsche with a ladder chassis and a fibreglass body, bonded to the steel frame for rigidity and achieving a drag coefficient of 0.34. Most cars were painted silver, the German racing colour, though the works cars first appeared in white. The bodies were made by contractors, unusually for Porsche: chopped fibreglass was sprayed into a mould, so thickness and weight varied from car to car. A race-prepared four-cylinder car weighed about 655 kg, reached 97 km/h in under six seconds and ran to 260 km/h with the tallest final drive, while frontal area was only 1.3 square metres.

The chassis used coil springs, the first Porsche without trailing-arm front and swing-axle rear suspension, with unequal-length A-arms in front, a 2,300 mm wheelbase and 275 mm front and 285 mm rear disc brakes on 15-inch wheels. Forty 1965 cars were built with a variant of the 911’s flat-six as the 904/6, and a few works cars took the 1,962 cc Type 771 flat-eight of 225 hp from the 804 Formula One car, though its flywheels had a disturbing habit of exploding. A 904/8-based Bergspyder was developed for the 1965 European Hill Climb Championship. The 904 won the two-litre GT class in the manufacturers’ championship in 1964 and 1965 and the prototype class in 1964, and it began the line of plastic-bodied Porsches that ended with the 917.

Design and features

• Fibreglass body on a ladder frame: bonded together for rigidity, with a drag coefficient of 0.34.
• Four-cam flat-four: the 180 hp Type 587/3, described as probably the most complex four-cylinder ever made.
• Road legal: sold as the Carrera GTS so that customers could drive it on public roads.
• Light and small: about 655 kg in race trim and a frontal area of 1.3 square metres.

Porsche 904 versions

• 904 Coupé (1963–1964): the standard four-cylinder car.
• 904/6 (1965): forty cars with a version of the 911 flat-six.
• 904/8: works cars with the 225 hp Type 771 flat-eight.
• 904 Bergspyder (1965): open hill-climb car based on the 904/8.

The 904 replaced the Porsche 718 and was followed by the Porsche 906. More cars are in the Porsche collection.

Sources

• Porsche 904, English Wikipedia: homologation, engine, chassis, production