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Mission Possible

It is a mission, almost a reason for existence, for a maker of a ultimate cars to create one as ultimate as possible according to the technology of the moment. That technology may vary according to the carmaker’s particular strengths, but the result will be a showcase of cleverness and a beacon of brand value. So we have the Ferrari Enzo, whose originally-intended name of F60 makes its ancestry clear. We shall soon have the Mercedes-Benz SLR McLaren, front-engined in typical Mercedes road-car style but structured in carbonfibre, and the monstrous 1,000 ps Bugatti Veyron, crown jewel of the Volkswagen Group.

Not to be left out in the supercar stakes with the advent of the Enzo, SLR and Veyron, Porsche unleashed the Carrera GT

And Porsche has its Carrera GT. It is mid-engined, and looks just a little like a giant Boxster, but the chassis is an entirely carbonfibre construction (more so than those of any of its notional rivals) and the engine is a dry-sump, 5,733 cc V10 originally intended for a Le Mans racing car.

The idea, as with the Enzo, is to deliver almost racecar experiences to drivers of road cars. Naturally, the claims for engine output and performance are startling: 612 ps (450 kW) at 8,000r pm, 590 Nm (435 lb ft) at 5,750 rpm, 330 km/h (205mph), from standstill to 100 km/h (62mph) in 3.9 seconds. True, an Enzo is slightly quicker again, as well as lighter than the 1,380 kg Porsche by 15 kg, but it is hardly an issue especially given the Carrera’s greater availability (1,500 examples to be built, left-hand drive only) and slightly less stratospheric price (around €400,000).

Another key difference is that the Carrera GT is an open car with centrally-split, lift-off roof panels which stow under the front hood. Despite this, its structure is still stiffer than that of any current closed Porsche. It is also the shiniest, neatest, least cluttered carbonfibre structure this writer has ever seen.

The carbonfibre chassis
The main construction is the central tub, which incorporates the front suspension mounts, the windscreen frame and the rollover bars as well as the sills, the bulkheads and the floor. It is narrow at the front, then expands to cabin width and terminates at the rear bulkhead. There are no visible reinforcements anywhere, not even for the front suspension mounts; the polished aluminium arms with their sealed rose joints sprout directly from a similarly shiny carbonfibre monolith. This apparently seamless tub weighs just 100 kg.

Bolted to it is the rear subframe and engine cradle. This, too, is a one-piece carbonfibre moulding despite all the gaps and struts, which starts at bulkhead width and tapers rearwards. It is the first rear subframe in a road car to be made of carbonfibre; there is almost no structural metal in this car.

Porsche did look at other options, including a tubular steel structure and an aluminium ‘spaceframe’ as used on the Carrera GT concept car that drove down the Champs Elysées on the eve of the 2000 Paris Show. However, neither gave the rigidity Porsche wanted if the Carrera was to be the ultimate provider of driving pleasure.

Building the whole structure from its 100-odd individually-cut pieces takes a week, building up the rest of the car takes another three, and the 500,000 elements analysed in the computer simulation of the 64 km/h (40 mph) offset impact test took seven 24-hour days of calculation. Porsche uses three different carbonfibre weaves in the Carrera GT: plain, twill (stronger but more flexible for moulding) and sateen which gives a very smooth surface. Twill weave is used the most, and there can be up to 10 layers, with alternating weave directions for strength, in high-stress areas.

Most of the chassis uses a honeycomb sandwich structure, of paper-like Nomex fibres in the main tub and the bonnet lid bonded to carbonfibre outer layers, and aluminium honeycomb in the rear subframe to resist engine heat. Here, the resin matrix is optimised to resist fuel and oil. Elsewhere the epoxy resin is designed to minimise the material’s tendency to absorb water, which among other things can cause the carbonfibre weave pattern to show through the paint finish in hot and humid conditions. Fortunately, the damage is usually reversible.

Like these major components the front and rear wings are heat-moulded in an autoclave, but they are not sandwiched. Smaller outer panels are vacuum-moulded by resin injection; for everything else, the carbonfibre is pre-impregnated with resin. The surfaces within the cabin are a hybrid carbonfibre/Kevlar aramid plastic fibre weave, because it resists splintering. Porsche uses five outside suppliers for its carbonfibre components.

Suspension: like a racecar’s
The front suspension owes much to racecar practice, with conventional Sachs coil-over gas dampers – no electronic variation of damper rates as used in the Enzo – which are actuated via bellcranks and stainless steel pushrods, as is the front anti-roll bar. The steering is powered, and the front hubs run not on a conventional stub axle but a hubshaft.

The rear suspension is similar, except that the lower track control arm is in tubular stainless steel hydroformed into a fatter middle and tapering ends. It is also flattened into an aerofoil section to help with the dynamics of the air heading towards the rear diffuser. Another racecar touch is that the left-side centre-lock wheelnuts are red and the right-side ones blue, because their threads are cut in opposite directions. All the stainless steel, including the two longitudinal front crash tubes, is a new H400 grade as high in quality as that used for cutlery, but with elasticity and ductility better suited to car use.

As in Ferrari’s Enzo and, optionally, a current 911, the brakes have ceramic composite discs. These are a third the weight of cast iron, heavier (by a factor of 1.5) than carbonfibre, but longer-lasting than both and giving the from-cold response required from a roadgoing brake. The wheels are the first on a road car to be of forged, rather than cast, magnesium, 25 per cent lighter than aluminium ones of the same strength. And while on the subject of metals, it is worth noting that the fuel tank is plasmatron-welded from deep-drawn aluminium pressings.

Keeping the weight down through the use of different metals has been very important to the car's design
The push-rod front suspnsion element at the monocoque bodyshell

Engine: conceived for racing
Porsche’s Weissach research and development centre developed a new V10 engine for a 2000 Le Mans project, but that project foundered when the race rules changed. Those changes did not outlaw this engine but they did alter aerodynamics, and the German carmaker’s resources were already being stretched by the Cayenne SUV whose Leipzig factory the Carrera GT will share.

The engine part of the programme, however, continued, still with its vee-angle reduced from a V10’s ideal of 72° to 68° (the narrower angle was used for aerodynamic packaging reasons). Still dry-sumped – as a 911 has always been, incidentally, the engine grew to 5.7 litres by means of a bigger bore in the Nikasil-coated cylinders, and gained Variocam continuously-variable inlet-cam timing to improve low-speed torque for road use.

As in the race car, so in the road car – for which no race career is planned: the engine’s narrowness allows room for aerodynamic ducts either side, plus an air supply for the various heat exchangers. That is one reason why a flat engine would not have been suitable. Another is that the V10, surprisingly, has a lower centre of gravity, because a ‘boxer’ engine typically has a cam-drive layshaft under the crankshaft.

Among the engine’s design features are titanium connecting rods, straight and vertical inlet ports, and cylinders bored directly into the closed-deck aluminium block because that is a stronger and more compact solution than using separate liners. One of each camshaft pair drives the other via spur gears, but this drivetrain is quiet because one gear per pair is sliced into two parts sprung against each other to take up the backlash.

Keeping the weight down low has been very important to this car'’ design. The six-speed, transversely-mounted transmission has all its other shafts below the level of the driveshafts; it also, incidentally, has a normal manual shift and a clutch pedal – and, in a world first, the twin-plate clutch has ceramic mating surfaces like those of the brakes.

However, the clutch’s composition is a little different from that of a brake disc. The carbon fibres are longer, to help withstand much higher revs, and its friction partner – a racing-like six-pad pair of titanium-backed driven plates – is designed to reduce friction as heat rises instead of increasing it, otherwise the grab and judder would be unacceptable. Lightweight and low rotational inertia are two advantages. A third is durability: the test programme included 16,000 starts, each transmitting 1, 000 ps for seven seconds.

Ceramic brake discs are moulded, but the clutch plates are cut out of board by water jets. That board is made by ‘pyrolising’ carbonfibre, then adding silicon which melts at 1020°C to a liquid thinner than water. At 1700°C the mix combines to form silicon carbide.

A power output of 612 ps (450 kW) drives the Carerra G to a top speed of 330 km/h (205 mph)
The six-speed transversely-mounted transmission has all its other shafts mounted below the level of the driveshafts

Body design: like the concept car
The exterior style is very obviously Porsche, and has changed little from the Paris Show car. The rear spoiler flips up by a massive 160 mm above 120km/h (75 mph) to increase downforce by 30 per cent, and a smooth underside helps manage a downforce which can reach 290 kg, split 30/70 front/rear, at maximum speed.

The carbonfibre seats weigh just 10.3 kg each, compared with over 20 kg for a regular seat, but they do not recline. Brake and clutch pedals are floor-hinged like an old 911’s, and made from aluminium extrusions much like those of a Lotus Elise. Porsche says more force can be applied more easily and over a shorter movement with the pedals thus configured. It matches the ankle’s arc of movement.

Pared-down road racer the Carrera GT may be, but its cabin is not a paean to skeletal starkness and naked componentry in the way of the Enzo. Bare carbonfibre is the finish for the broad sills and the lower part of the central spine, but otherwise the view is of leather and magnesium. The centre console is finished with a hot-pressed magnesium cover in which the Carrera GT’s prodction number is etched, and the door handles and most of the knobs and switches are also of the lightweight, warm-grey metal.

There is wood in the gearlever knob, though, a nod to the lightweight balsa-wood item used in the fearsome 917 race cars. However, they did not have an optional Bose Online Pro stereo and navigation system weighing just 1.5 kg – plus speakers.

On test at Weissach
Chief test driver Roland Kussmaul says that the Carrera GT can lap the Nürburgring Nordschleife in seven minutes and 30 seconds, and describes the engine as delivering so much torque that “You can drive it in sixth gear all the time”. It nevertheless has a very quick throttle response, to judge from this writer’s observation of Kussmaul’s demonstration laps at Weissach

The sound is the harmonic warble typical of a double five-cylinder engine, hard-edged and high-pitched as the rev limit approaches. There is a taste of a Formula One car’s aural ferocity here, albeit well attenuated, and Kussmaul exploits all of it in ample demonstration of the Carrera GT’s power-oversteer properties. An exciting time is guaranteed for those affluent enough to own one.