The Porsche Carrera GT | Part Five

The Porsche Carrera GT

Porsche Carrera GT

Thoroughbred ten-cylinder racing engine

The ten-cylinder dry sump power unit behind the cockpit of the Carrera GT has a genuine competition heritage – it is based on a 5.5-litre V10 normally-aspirated engine as raced in the Le Mans 24 Hours. Capacity has been increased to 5.7 litres to give the production car tremendous performance, enabling the Carrera GT to meet all requirements needed for circuit racing yet, at the same time, providing all the qualities required in everyday motoring. Indeed, the Carrera GT proves its supercar status through its performance figures alone – maximum output is 450kW (612bhp) at 8000rpm, maximum torque 590Nm (435lb ft) at 5750rpm. Top speed is 330km/h (205mph), and the Carrera GT sets new standards with its standing start acceleration: 0 – 100km/h takes just 3.9 seconds and 0 – 200km/h is covered in a staggering 9.9 seconds.

The angle of the cylinders has been optimised at a 68 deg V, which in conjunction with its low mounted crankshaft, helps give the engine the very low centre of gravity required on a car of this calibre. A narrow cylinder angle was also needed to provide sufficient space to fulfil the required aerodynamic considerations. Porsche opted for a V10 with four valves per cylinder and aerodynamically designed intake ducts to provide optimum conditions for the cylinder charge cycle. Built at the Porsche engine plant in Stuttgart-Zuffenhausen, the ten-cylinder engine is a load-bearing component of the car and so has an extremely stiff engine block and housing. One further advantage is that the cylinder bores remain absolutely stable and almost entirely free of any distortion. Perfect for the race track yet optimised for the road.

The lightness of the power unit makes a significant contribution to the ideal overall weight of the Carrera GT. Weighing just 214kg (472lb), the engine is made exclusively of light alloy combining supreme strength with equally outstanding resistence to temperature. Bore and stroke figures of 98mm (3.86ins) and 67mm (2.99ins) respectively provide the overall engine capacity of 5733cc while the forged crankshaft, designed for minimum mass inertia, offers maximum torsional stiffness. The pistons themselves are connected to the crankshaft by titanium conrods combining superior strength with low weight for outstanding refinement and a long, dependable service life despite engine speeds of more than 8000rpm.

Innovative six-speed manual gearbox

A six-speed manual gearbox has been developed especially for the Carrera GT. Fitted transversely at the rear of the car, it transmits the enormous power of the engine smoothly and consistently to the road. Exceptionally compact and with the lowest possible centre of gravity, the gearbox also contributes to the car’s optimum weight distribution. Thanks to competition requirements that demand a clutch as compact as possible, the Carrera GT does not have a two-mass flywheel – but the benefits of such a flywheel is nevertheless provided by the special design of the input shafts. The main shaft is hollow and has a long, thin shaft running inside acting as a spring rod. Together the two shafts serve as a torsion spring to absorb possible engine vibrations and reducing transmission noise in the process.

The use of ball bearing-mounted Flexball shift cables is yet another worldwide automotive first. Unlike conventional shaft cables with a wound steel core, a Flexball cable is made of a flat stainless-steel band resting in ball bearings at each end. This allows the transmission of movement even over longer distances with no frictional losses worth mentioning, providing a very high efficiency rating of 96 per cent.

Another world-first achievement: the ceramic clutch

The Carrera GT is the first car in the world with a ceramic clutch – the lightweight Porsche Ceramic Composite Clutch (PCCC). One of its special features is the small clutch plate measuring just 169mm (6.56ins) in diameter helping to give the entire drive unit a very low centre of gravity, while its low weight has positive effects on the car’s dynamic qualities. Prior to the development of PCCC, the only clutch capable of meeting the rigorous demands of motorsport was made from carbon-fibre but had a much shorter service life and would not have provided the everyday driving dependability vital to the Carrera GT. PCCC, however, exceeds even the service life of conventional clutch plates. In developing this new technology, Porsche engineers have benefitted from experience with Porsche Ceramic Composite Brakes (PCCB), at the same time as continuing the development of the material, making it suitable for a two-plate dry clutch with a long lifespan.

continues... | Part Six
Published 1 June 2004 Melanie Carter

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