Porsche 918 Spyder races toward production

OK, let's put the usual arguments to rest first: The Porsche 918 Spyder is going to be even faster than the Carrera GT in a straight line. That's based on Porsche's own computer simulations in anticipation of the production version of the gasoline-electric-powered 918 Spyder, which is due to roll off a dedicated line within a decommissioned paint shop at Porsche's Zuffenhausen, Germany, headquarters next year. The claimed 0-to-62-mph time is 2.8 seconds; 0-to-124 mph is 8.9 seconds, and top speed should be about 202 mph, thanks in part to series of active aerodynamic functions, including a multistage rear wing. More remarkable perhaps is the figure Porsche is touting for the Nürburgring—still the ultimate test of any car's dynamic prowess. Frank Walliser, head of the 918 Spyder's development and intimately involved in the development of the Carrera GT early last decade, reckons that it is good for a scorching 7-minute, 22-second lap of the old Nordschiefe circuit. On standard road tires..That's 10 seconds inside the best time recorded by its direct predecessor and even beats the 911 GT3 RS hybrid, with its fandangled flywheel-based hybrid system. As if that's not enough, Porsche also says its new supercar will boast a combined city/highway fuel-consumption figure of more than 78.4 mpg (U.S.) on the current European cycle. By comparison, the Carrera GT returned just 13.2 mpg (U.S.) under the same test procedure. The spyder achieves this by using electric drive, in which it has range of 16 miles at speeds up 93 mph, giving it the sort of environmental credentials unmatched by any existing supercar with similar levels of performance. The initial building blocks of the 918 Spyder were set around Porsche's RS Spyder race car, victorious in the ALMS LMP2 championship in 2007, 2008 and 2009. As Walliser reveals, “We wanted to see how far we could push the envelope in providing a direct link between the road-car side of our business and motorsport program—a step beyond what we had already achieved with the Carrera GT. A lot of factors were fluid to begin with, but it was clear from the outset of the project that the engine of the RS Spyder would be used in one form or the other. We just didn't know to what extent and just what role it would play at that stage.” As word began to circulate around the industry in 2009 that rivals Ferrari, McLaren and Lamborghini were planning new-age supercars boasting some form of hybrid drive to enhance performance, former Porsche R&D boss Wolfgang Duerheimer, set about forming a core team of engineers whose job was to investigate the possibility of combining a production version of the RS Spyder's highly strung naturally aspirated 3.4-liter V8 engine with an advanced electric drive system to create the German carmaker's most radical road car ever. Many of those chosen to work on the 918 Spyder previously were involved on the Carrera GT—but all will tell that you the two cars are vastly different beasts, the former combining the best of Porsche's racing and road-car technologies with the latter focused purely on bring race-car technology to the road. The first driveline conceived for the car to replace the Carrera GT bench-tested at Porsche's Weissach skunkworks in Germany was based around a conventional gasoline-electric hybrid arrangement and first ran back in 2010, according to Walliser. But as the project progressed into 2011 it was switched to a more complex plug-in gasoline-electric hybrid system as previewed by the 918 Spyder concept car, which stole the spotlight at the Geneva motor show that same year. The only fully functioning 918 Spyder in existence is a ragged-looking thing, with its makeshift bodywork, exposed plumbing, miles of seemingly unorganized wiring, top-exiting tailpipes and shiny aluminum box sitting up back housing the control unit for the electric drive. But looks can be deceiving: Behind the improvised appearance lurk some of the most high-tech materials, construction techniques, propulsion technologies and electrical solutions ever considered for a road-going car. The description “rolling laboratory” never seemed so appropriate. All that's missing are the white-coated laboratory technicians. Achieving the lightest weight, an extremely low center of gravity, high torsional rigidity and the most downforce of any road-going Porsche have been the four guiding principles during the development of the 918. The monocoque, produced at Carbo Tech Composites in Austria, is claimed to weigh 485 pounds. Unlike the structure used by the Carrera GT, it boasts an asymmetrical design, with the length of the passenger seat well is shortened slightly compared with that of the driver-seat well in a move taken to house the fuel tank. “We would have had to give up three liters (0.8 gallon U.S.) in tank capacity with a conventional design. As it is, we've managed to package a 70-liter (18.5-gallon U.S.) tank behind the passenger seat over the battery pack,” Walliser says, adding, “and at that capacity we have managed hit our range target.” Productivity improvements mean up to five monocoques can now be cured per week. Back in the days of the Carrera GT, it took five days for one monocoque. At the heart of the new Porsche is a heavily modified version of the RS Spyder's 90-degree V8 gasoline engine known under the code name M18. Housed longitudinally behind the battery pack but in front of the rear axle on a carbon-fiber cradle attached to the monocoque by six mounts, it has an added 1.2 liters of capacity over the original race-spec unit, taking it up to 4.6 liters. Peak power for the combustion engine is put at 562 hp, giving it a specific output of 122 hp per liter—11 hp per liter more than the Carrera GT's 612-hp, 5.7-liter V10 engine. With a 9,200-rpm redline, it was designed to offer searing top-end properties in line with the original brief to give the 918 Spyder at least a whiff of the RS Spyder race car's overdriving excitement. Together with the changes made to the internal architecture of the engine, Porsche also developed a radical new exhaust system for the production version of the 918 Spyder. Revealed on the engineering mule here for the first time, it routes the exhaust above the engine with so-called top pipes rather than the side-pipe arrangement hinted at by the earlier concept car. The reason for the change centers on concerns about excessive heat buildup around the battery pack. It also allowed Porsche to give its new gasoline engine unique thermodynamic properties, with the hot side of the exhaust located on the inside of the cylinder banks and the intake tracks on the outside. Bolted to the rear of the low-mounted gasoline engine is a cylindrical-shaped synchronous electric motor offering an additional 121 hp. Drive from the combustion engine and rear electric motor is channeled to the rear wheels via a heavily modified version of Porsche's seven-speed dual-clutch gearbox as used by the Boxster, the Cayman and he 911. Engineered in partnership with German specialist ZF, it was turned end-on-end and upside down in a move that required a thorough reworking of its lubrication system. In the words of Walliser, “The changes are such that it's virtually an all-new unit.” A second electric motor with 107 hp is set up front, acting on the front axle via a direct gear and providing the 918 Spyder with all-wheel-drive capability, although drive is disengaged to the front wheels at speeds of more than 146 mph to aid stability. All told, there is a combined system output of about 759 hp and 568 lb-ft of torque. As previewed by the earlier concept, the production version of the new top-of-the-line Porsche will offer no fewer than five different driving modes: E power, the default mode when it is started as long as there is sufficient battery charge and offering pure electric propulsion; hybrid, a combination of both gasoline-engine and electric-motor propulsion but with the capability to run on pure electric propulsion when the conditions allows; Sport Hybrid, again a combination of both the gasoline engine and electric motors but with the former in constant operation and without the capability of pure electric propulsion; Race Hybrid, in which the full force of the gasoline engine is boosted by the electric motors; and Hot Lap, which allows the driver to call up all of the battery pack's energy for maximum performance. As a parallel hybrid, like the Cayenne and the Panamera, the 918 Spyder can run on either gasoline or electric, or a combination of the two. It is also capable of running in either rear-wheel or all-wheel drive, dependent on the conditions and the selected driving mode. In rear-wheel drive, the gasoline engine and/or the rear electric motor provide the power. In all-wheel drive, the front electric motor is engaged to provide power to the front wheels. A torque-vectoring system is used to apportion drive on both axles, with the rear equipped with a mechanical locking differential. Energy for the electric motors is provided by a 6.8-kilowatt-hour lithium-ion battery pack mounted low down directly behind the rear bulkhead in a position aimed at giving the 918 Spyder the best possible center of gravity. Consisting of 312 individual cells supplied by SB LiMotive (a Stuttgart-based joint-venture company operated by Samsung and Bosch) each weighing 0.4 pound, it provides a maximum 202 kilowatts and stores energy created both on the run and through plug-in means via a socket located in body covering on the right-hand side rollover hoop. The complete plug-in hybrid system--including the electric motors, battery pack and all of the various electrics--is claimed to add 695 pounds to the curb weight. Recharging time for a fully depleted battery pack is said to vary between two and half and six hours, depending on the available voltage. “We're used to fast driving, so fast charging fits the Porsche mantra,” jokes Walliser, who says Porsche is also considering an ultra-high-voltage system that could conceivably provide a full charge in less than 30 minutes. A complex cooling system consisting of no less than five radiators ensures that the driveline is always kept at an optimum operation. Included are two radiators up front in the nose, a further two in the right-hand flank and one on the left-hand flank. An additional radiator is used for the air-conditioning compressor, although it does not serve any purpose in the cooling of the driveline or the battery pack. Mechanical and electric components aside, the 918 Spyder's advanced aerodynamics play a crucial role in seeing it achieve Porsche's lofty performance targets. As Walliser explains, “It's not so much a reduction in drag but a question of how much downforce can be generated.” The front air ducts get active diffusers that remain closed for added aerodynamic efficient until sensors detect rising driveline temperature, at which they open to allow cooling air to flow to the radiators and the front brakes. The rear spoiler, not evident on the mule we got to drive in but described as a central element of the production car, also offers varying levels active downforce in four different steps, not only in height but in angle, too. From a nominal fully retracted position with a 2-degree angle of tilt, it initially extends out by 0.8 inch at the same 2-degree angle. At higher speeds, it extends out by 4.7 inches, with the angle increasing to 6 degrees. At its most extreme position, at which overall downforce is said to improve on the Carrera GT by a considerable 15 percent, it remains at a height of 4.7 inches but receives a more extreme 10-degree angle of tilt--a position that is claimed to provide more than 449 pounds of downforce on the rear axle at the 918 Spyder's claimed 202-mph top speed. The concept car's vivid green-painted brake calipers were meant to signal an advanced kinetic-energy-recuperation system. They're plain metallic grey on the first prototype but apparently no less effective. The eight- and four-piston units operate on 16.1-inch-by-1.4-inch front and 15.4-inch-by-1.3-inch rear vented and cross-drilled carbon-ceramic discs. Supporting the new car is an all-new aluminum-intensive suspension system. It uses a wishbone layout up front with conventional spring and dampers rather than the race-car-derived push-rod arrangement seen on the Carrera GT. The rear, meanwhile, receives multilinks designed to enable a wide diffuser element to be mounted aft of the gearbox for added aerodynamic efficiency. In line with Porsche's aim to give its new supercar true everyday usability, the 918 Spyder also get variable-rate dampers and a lift system that allows the driver to raise the front of the car by up to 1.2 inches for improved curb clearance. As part of many fuel-saving technologies on board is a new electromechanical steering system based around that used by the new Boxster and the 911 but combined with a new rear-wheel steer feature that Porsche is claiming will provide class-leading levels of agility. At low speeds, the new system steers the rear wheels in the opposite direction to the front wheels, making cornering responses more direct, faster and precise, while reducing the turning circle for added maneuverability around town. At higher speeds, it steers the rear wheels in parallel to those up front, reducing the tendency for oversteer. The 918 Spyder is a huge undertaking, even for a company with such a spectacular engineering pedigree as Porsche. But on the evidence of the first rolling-chassis prototype, an admittedly shabby-looking one at that, all of the essential elements appear to be in place. By the time you read this, Porsche will have begun construction of road-legal prototypes of its new supercar from where the development process will kick into top gear, with testing planned to take place on four continents over the next 18 months. And you can be sure that we'll be charting its progress.