Porsche doesn’t have to build this car. The 918 is a risk — a giant risk, in fact. Porsche is at the top of its game right now with the new 911 and Boxster, and no one out there with piles of disposable income is asking for a hybrid supercar. I would go so far as to say the situation is quite the opposite. But aside from some misshapen headlights on the 996 series 911, Porsche is not in the habit of making mistakes. If this project turns out badly, it could do irreparable damage to the legendary German sports car manufacturer’s reputation. If it turns out as planned, it will not only redefine hybrids as we know them, but the world of supercars as well.
To make this easier on everyone, let’s skip the argument about the value and usefulness of your neighbor’s hybrid and just agree they’re here to stay, and most of us will be driving one in some form or another by the end of the decade. Stop the groaning; it doesn’t have to be bad. The Prius is boring, but not because it’s a hybrid. If the Prius were powered by a 300-hp V-6, it would still be boring. Hybrid technology itself isn’t bad and can be used just as much for performance as for being green. Ask 10 race fans their favorite images of endurance racing, and least six of them will say something about glowing cherry-red brake rotors in the twilight hours on the Mulsanne at Le Mans. But as much as we all love those rotors, they’re a prime example of why we need hybrids. All that pretty red light beaming off the rotors is energy the car has lost and will never regain.
Generally speaking, a hybrid captures a portion of that energy through brake regeneration, stores it in a battery, and dispenses it back through electric motors. But the 918 isn’t just about slapping a battery and electric motors onto a sports car. This is the most technologically advanced car Porsche has ever built, and it might be a greater leap today than the 959 was back in 1986. The technology, from drivetrain, to chassis, to aerodynamics, and especially its power delivery system, will find its way into future Porsche products. The 918 isn’t about Porsche building a run of supercars and calling it a day. It’s about developing new tech for the next generation.
Like most modern prototype race cars, the 918 is built around a composite monocoque — essentially a high-tech bathtub. The tub is built from Resin Transfer Molded Carbon Fiber Reinforced Plastic, or RTM CFRP. The dry carbon-fiber material is placed in a mold and the liquid matrix is pumped in while a vacuum pump simultaneously evacuates the air. This method minimizes voids — areas where the fibers are not surrounded by resin — and maximizes the fiber to matrix ratio. It isn’t the most advanced method (Formula 1 uses a different process), but it is the best for mass production vehicles.
The rear of the 918 uses an RTM subframe to mount the powertrain, and aluminum crash structures are mounted at both front and rear. The strength of the car comes completely from the monocoque. The two-piece removable carbon-fiber roof is simply to keep the sun off the driver and protect his or her undoubtedly well-coiffed hair. It does seem like a shame to take the roof off the car, because Porsche did so much wind tunnel work. The 918 has three distinct aerodynamic modes. The first is an efficient mode that creates the least amount of drag by lowering the rear wing and closing off underbody ground effects tunnels.
Sport mode creates the highest level of down force by raising the rear wing and increasing its angle of attack. It also utilizes flaps at the front of the car to feed air to the underbody of the car, creating downforce with a diffuser at the rear of the car. The last mode is for the highest top speed possible, and reduces the angle of attack on the rear wing but keeps it extended. Also in an effort to reduce drag, the side vents in the front fascia are able to open and close depending on cooling needs. In most conditions they will remain closed to push air around the car rather than through it. But the designers insisted they open when the car is at rest for aesthetic reasons.
Porsche has worked to keep the car’s mass low and centralized. The 918 has the lowest seating position of any Porsche road car ever. The driver’s most sensitive piece of feedback-gathering equipment is located fewer than 7 inches above terra firma — think about that when you’re pounding along at triple-digit speeds. The drivetrain is mounted as low as possible, which required flipping the gearset in the car’s seven-speed PDK transmission. The engine uses a dry-sump oiling system, not only for more effective scavenging under high-g loading and less parasitic loss from crank splash through, but also to decrease the engine height.
Everything about the 918 is low and tight. Porsche engineers reinforced the idea of package density. Every cubic inch of the car’s volume is utilized beneath its carbon-fiber skin. The 918 has a total of 55 different computers sending signals through nearly four miles of wiring. There are three different cooling circuits. The lowest temperature system is for the battery and electronics. The medium temperature system is for the electric motors, and the high temperature system for the gasoline engine. Additional cooling radiators are used for engine oil and transmission fluid.
All of these systems are packaged as close to the center of the vehicle as possible to reduce the 918’s polar moment of inertia. (The lower the polar moment of inertia an object has, the easier it is to rotate.) Porsche has positioned the 6 kW-hr battery directly behind the passenger compartment, along with the 18.5-gallon fuel tank. The 4.6 liter V-8 is mounted as far forward as possible and is able to snug up closer than any other engine, thanks to its complete lack of drive belts. And that isn’t all the engine has going for it. Based on the power plant from the RS Spyder LMP2 race car, the flat-crank V-8 churns out 580 hp and spins all the way up to a 9000 rpm redline.
Mounted between the gas engine and the PDK transmission is a 125-hp electric motor that also serves as the car’s main generator. This motor can function parallel with the gas engine or in combination with a front-mounted 115-hp electric motor to power the car. The rear motor drives the car through the transmission and uses all seven gears, as does the gas engine. The front motor is a direct drive unit with a single speed and an electric clutch to decouple when not in use.
Since it’s a single speed, the front motor is forced to decouple at high speeds. Porsche feels it isn’t worth the weight and extra complexity to use a two or more speed transmission in front. Since the two motors are not mechanically coupled, Porsche has been playing with what it calls “stretch” in the driveline. When cornering at the limits, the car is able to intentionally drive the front and rear axles at different speeds and not just push torque around like in traditional all-wheel-drive systems. Apparently this new version of torque vectoring is still in the experimental phase but should bring some interesting results.
The 918’s rear differential uses a more conventional torque vectoring system with an electronically controlled differential pushing power from side to side. The front end still uses braking force for vectoring with an open front differential. To complement the torque vectoring, the 918 employs electrically operated rear wheel steering. The engineers won’t give exact numbers, but apparently the car dials in a few degrees at most, even at low speeds.
It sounds as if this is an intelligent, variable alignment system more than what we would normally consider rear steer. Something similar to an active version of the Weisach Axle Porsche developed in the 1980s. Instead of having a fixed kinematic gain through the suspension’s range of motion, the system can dial in toe as needed, regardless of suspension displacement. Speaking of suspension, the 918 is using control arms in the front and rear. The production version will use the latest version of PASM for adjustable damping rates like other Porsche models.
The cars present during this demonstration were equipped with standard dampers. The thrust from electric power only is impressive. It feels at least as fast as the base Boxster — maybe faster. All the immediate torque from the electric motors will surely make this an absolute animal from 0 to 30 mph even if you are in Save the Planet mode. Pure electric driving wasn’t nearly as quiet as I thought it would be. The gear whine reminded me of being in race cars with straight-cut gears.
The tires make a decent hum, and because these are still test cars, the NVH attenuation is no where near finalized. After the test driver told me about the joys of all-electric driving, and how this car qualifies to be driven around in London in “car-hating” zones, and how the birds are greener and the grass sings sweeter with a plug-in hybrid, a quick touch of the steering wheel-mounted control switches the car into sport mode. The V-8 fires up, shooting carbon into the atmosphere with beautiful explosions of gasoline and air. The sound is raucous and primal. Right now the 918 has just enough muffling to be street-legal, and that is questionable. Suddenly its acceleration is nearly 997 Turbo S-brutal.
The 918 is compliant over rougher sections of the twisty back roads, but with the low center gravity and resulting small roll couple, body roll is minimal. Without driving the car it’s tough to comment on steering accuracy or linearity, but watching the steering wheel, it looked as though minimal inputs were required. Porsche has balanced the car with 57 percent of the weight biased over the rear axle. Although the weight is very centralized, that rear bias is noticeable, especially with the seating position farther forward than you might normally be accustomed to. The weight tends to favor the outside rear corner in turns and you feel the typical Porsche pull from behind your hips as the CG wants to rotate the car in turns.
The front propulsion wasn’t perceptible, but again, this was from the passenger seat. I have no doubt this will soon prove to be the fastest production Porsche ever. After the ride, a Porsche test driver emerged from nowhere with a flash from his chrome yellow helmet with a mirrored gold visor. Apparently this was going to be his first time in the 918 around the Ring, and the engineers looked nervous about his performance. Porsche was hoping to run a 7:22 during the session. Those savvy in the ways of the Nordschleife will recognize that time as exactly what Porsche claims the 997 GT2RS will put down around the circuit. The 7:22 was conservative at best, and after a single warm-up lap, the prototype turned in a 7:14. That lap puts it into some pretty serious territory with cars that can barely be considered mass-production street cars.
Porsche says the 918 is currently about 80 percent complete. The only parameter that is finalized is its exterior design — everything else has room to play. The engineers tell me they have room to add power and efficiency, and could even shave weight off the car. Right now, internal discussions center around whether the car is already fast enough, and if efficiency should be the focus. So far, Porsche says the car has registered a 78 mpg rating in European fuel economy testing. It is also apparently capable of a 3.0-second 0-60 mph time, which translated from Porsche to real-world is likely a couple of ticks lower.
It will be interesting to see how the car develops from here. Porsche is already planning a Weissach Package that will shave nearly 80 pounds off its claimed 3747-pound weight. I hate to put Porsche on the spot, but when everything is said and done, it wouldn’t surprise me if we see a 7:10 around the ‘Ring, maybe lower. While the 918 is clearly a big risk and a monumental undertaking, I am happier this car will be defining what a hybrid is and how its technology can be applied to future models. This is clearly about optimizing performance, which goes hand in hand with optimizing efficiency. Suddenly the prospect of a hybrid 911 isn’t so scary.