NAIAS Highlights: Production
Another powerful Porsche
The 911 GT2 that Porsche debuted boasts a top speed of 315 km/h (195 mph) and takes only 4.1 s to reach a speed of 100 km/h (62 mph). Although based on the 911 Turbo's 3.6-L six-cylinder boxer, the GT2's engine was modified to deliver 340 kW (456 hp) at 5700 rpm - an additional 31 kW (41 hp). Maximum torque is 620 N•m (457 lb•ft) from 3500-4500 rpm, compared with the 911 Turbo's 563 N•m (415 lb•ft) from 2700-4600 rpm. Maximum engine speed is 6750 rpm.
In comparison with the all-wheel-drive Turbo 911, the rear-wheel-drive GT2 is 100 kg (220 lb) lighter for a weight-to-power ratio of 4.23:1. The GT2 has larger front air intakes and a new air intake just forward of the front hood. Its dual turbochargers provide greater throughput than the 911 Turbo's, allowing an increase in turbo boost pressure at full load to 200 kPa (29 psi). Larger intercoolers keep the air-charge temperature consistent despite the increased boost pressure. At the GT2 engine's power peak speed of 5700 rpm, boost pressure reaches 194 kPa (28.2 psi) and then peaks at over 6200 rpm. As a result, the GT2 maintains an almost consistent power level even above the engine's power peak speed despite the increase in exhaust back pressure at such high speeds.
The light-alloy crankcase is split vertically, with the crankshaft running in eight main bearings. The crankshaft is linked to the light-alloy pistons via forged connecting rods, reducing the weight of moving masses within the engine to produce good throttle response. The light-alloy pistons reciprocate in Nikasil-coated, light-alloy bores designed to reduce friction. Each combustion chamber has two inlet and outlet valves arranged in a V configuration that are actuated by twin overhead camshafts per bank of cylinders. All valves feature dual springs to ensure proper closing at high speeds, while the use of hydraulic tappets eliminates the need to adjust valve clearances.
VarioCam Plus, the latest evolution of the Porsche VarioCam variable-valve-timing system, now features variable-valve lift to deliver maximum torque and power at all engine speeds. It also helps improve fuel economy. Dry sump lubrication ensures a reliable supply of oil to the engine, even under extreme lateral and longitudinal g forces. Two scavenge pumps in each of the cylinder heads combine with a central return pump with twin extraction points in the crankcase to return the oil quickly and efficiently to a separate oil tank. A further pump supplies the lubrication points in the engine directly. Oil is defoamed by means of an oil separator integrated into the oil tank.
The Motronic ME 7.8 electronic engine management system manages intake air pressure and controls the electronic throttle across the entire rpm range. It also helps control the VarioCam Plus and cylinder-selective knock control systems.
The engine is an evolution of the race-proven unit that powered the 911 GT1 to a one-two finish at Le Mans in 1998. It features dual overhead camshafts per cylinder bank, four valves per cylinder, coil-on-plug ignition, and sequential fuel injection with separate fuel mixture for each cylinder bank. The bore is 100 mm (3.94 in), the stroke is 76.4 mm (3.0 in), and the compression ratio is 9.4:1.
A race-proven, cable-operated gearshift mechanism allows for smooth gear changes while eliminating the transfer of vibration from the engine and six-speed gearbox to the passenger compartment. The clutch is paired with a dual-mass flywheel for an even smoother ride. For racing use, all gear ratios can be replaced to suit individual circuit characteristics.
Another motorsports-derived innovation is the transmission lubrication system and oil/coolant heat exchanger, which are designed to maintain optimum temperatures in the gearbox during the toughest competition use.
An asymmetric differential lock helps maximize performance by delivering 40% lock under power to improve traction, and 60% lock when coasting to stabilize the car. The GT2's center of gravity is about 20 mm (0.8 in) lower than the 911 Turbo's, and a revised spring and damper system is employed.
Use of lightweight construction throughout has kept both total weight and unsprung weight to a minimum. Reducing unsprung mass automatically improves spring and damper response, making for better road-holding as well as more reliable feedback to the driver.
The tried-and-tested McPherson-strut front suspension and race-proven, subframe-mounted multilink rear suspension feature a special spring and damper configuration to ensure optimum traction on variable road surfaces. For track use, the adjustment range of the front and rear suspension has been increased so that the new 911 GT2 can be fitted with racing tires. Setup options include ride height, camber and track, as well as five-stage (front) and four-stage (rear) antiroll bars. The dampers can also be used in conjunction with racing springs.
A restyled front spoiler and dominant rear wing mark exterior changes. An extensive amount of wind tunnel work enabled engineers to optimize the balance between drag (Cd=0.34) and downforce on the front and rear axles. To create the best possible aerodynamic balance between front and rear, the GT2 features an ultralow front spoiler made from a flexible composite material. The role of this spoiler is to minimize the amount of air that flows underneath the car and thus reduce lift on the front axle. At the rear, the GT2 benefits from two key aerodynamic features: a small lip on the engine cover and a large wing-type spoiler with an angle of incidence adjustable by up to 5°.
Cooling air is delivered to the radiators via a highly effective internal airflow management system derived from the race-winning 911 GT1 and 911 GT3 RS. The racing origins of the system are acknowledged on the exterior of the car with the distinctive air outlet located in front of the luggage compartment lid. Twin inlets on either side of the front spoiler are used to channel air to the ceramic brakes. As on all 911 models, polypropylene underbody paneling is used to enhance the aerodynamic properties of the car.
The GT2 comes with the most effective braking system ever featured on a production Porsche: the Porsche Ceramic Composite Brake (PCCB). It is made of a specially treated carbon fiber silicated in a high-vacuum process at approximately 1700°C (3100°F). The PCCB disc is cross-drilled and internally vented, and offers a weight saving of more than 50% over conventional alternatives. Since this weight is unsprung, the PCCB automatically improves agility and handling.
Another feature of the system is the innovative new composite brake pad, which combines with the ceramic disc to deliver high and constant levels of friction under braking. With the replacement of conventional metal components with composite pads and discs, temperature is no longer a factor in brake performance. This not only helps minimize braking distances, but also ensures safer deceleration from high speed and virtually eliminates the risk of brake fade.
In an emergency stop, PCCB immediately delivers maximum stopping power to the road. Abrasion is very low compared with that of metal discs, with each PCCB disc offering a service life of approximately 300,000 km (186,000 mi). The new composite brake pads also last about twice as long as conventional ones. The PCCB pads do not absorb water, enabling good performance in wet conditions.
- Patrick Ponticel
