Smaller than a Golf and lower than a Boxster, Volkswagen's XL1 looks like a bijou supercar. It has a sleek, thigh-high, carbon-fiber composite body, butterfly wing doors, a mid-mounted powertrain, and a seven-speed dual-clutch transmission. The XL1 is a supercar of a different sort, though. It won't hit 200 mph, but it will go more than 200 miles on a single gallon of diesel.
In fact, on the official European combined driving cycle, the XL1 is rated at 261 mpg. European and American fuel-consumption tests are quite different, but VW engineers say an equivalent combined EPA city/highway number would be about 20 percent lower -- say, 209 mpg. What does that mean? It means you could drive the 2800 miles from Santa Monica Pier to downtown Manhattan on about 55 bucks' worth of fuel. And a bit of electricity.
Perhaps what's most remarkable about this little diesel/electric plug-in hybrid, however, is that it wouldn't be stuck in the freeway slow lane the whole way. With a combined system output of just 68 hp and 103 lb-ft, acceleration is understandably modest -- VW claims 0-60 mph takes about 12.5 seconds -- but during our brief test drive, the XL1 was content to happily bowl along a Swiss freeway at 70-75 mph, the diesel twin purring at a little over 2100 rpm. The XL1's top speed is electronically limited to 100 mph.
Duck under the door and into the cabin of the XL1, and you're greeted with a lot of familiar-looking VW hardware, right down to the instruments and switchgear, though most of it is actually bespoke to the XL1. The steering wheel is small, with a flattened base, and the DSG shifter looks like a three-quarter-scale version of the one you'll find in a Golf GTI. The small, fixed nav screen is the Garmin unit from the Up!, VW's cute little city car.
You don't so much fire the XL1 up as switch it on. The hybrid system gives primacy to the 27-hp electric motor wherever possible. Squeeze the long-travel accelerator pedal and the XL1 oozes away with a distant high-pitched whine. The 47-hp, 800cc parallel twin diesel -- architecturally, it's one half of VW Group's 1.6-liter TDI four -- sounds like one of those air mattress inflation pumps when it first fires up, a rapid chocka-chocka-chocka-chocka-chocka-chocka in your right ear.
The electric motor is situated between the diesel engine and the seven-speed DSG transmission. At low speeds and with modest accelerator inputs, the XL1 will run a considerable distance solely on electric power before the diesel kicks in. Press a button, and the XL1 will stay in pure EV mode for up to 30 miles, courtesy of a 5.5-kW-hr lithium-ion battery pack allowing emissions-free running in city areas. Management of the power flow is impressive: Only when the chocka-chocka of the little diesel overwhelms the whine of the electric motor are you aware of any change in how forward motion is being accomplished. The transitions are smooth and seamless.
Just like any supercar, the XL1 demands compromises. It's noisy because there is very little sound deadening, which helps keep overall weight to just 1750 lb. Not only do you clearly hear both engines, but you also hear the tires on the pavement, the suspension working over the bumps, and the curious rasp of the tiny carbon-ceramic disc brakes as you came to halt. VW engineers considered an active noise cancellation system, but discarded the idea because of weight and the fact that it would consume precious power. Mechanical noise is part of the XL1 experience, just like it is in a Pagani Huayra.
What you don't hear much of, however, is the wind. With a Cd of just 0.189, the XL1 is the most aerodynamic production car in history. It cleaves the air like a hot knife through butter, and, at 50 mph or more, the dull roar of the tires effectively cancels out any engine noise.
It's been many years since we've driven a new car without power steering, so the XL1's manual system is at first a bit of a shock. It's heavy in tight turns at slow speeds, and loads up in faster corners. But you do know exactly what's going on with the front tires. It's old school and kind of entertaining. The regenerative braking system, by contrast, is almost state of the art in pedal feel and consistency.
VW has not announced a price for the XL1, saying only that it will offer what it calls "innovative financing" to get customers into the car, and that just 250 will be virtually hand-built on a special production line at VW's Osnabrück plant in northwestern Germany. Simple auto industry economics suggest this is easily the most expensive Volkswagen ever made -- after all, supercar technologies mean a supercar price tag -- and that it's a money loser. So why build it? "It's a lighthouse car," says VW Group R&D chief Ulrich Hackenberg. "This is the technology spearhead of the VW Group, and all the brands will benefit."
Hackenberg says lessons learned creating the XL1 -- in perfecting the ultra-lightweight body construction, in developing the diesel/electric plug-in hybrid powertrain, in finding the 1001 efficiency tweaks so that it needs just 8.3 hp to travel at a constant 62 mph -- are already being cascaded across the Volkswagen product portfolio. For example, at the VW Group Night extravaganza on the eve of the Geneva show where the XL1 was the star, Audi announced a plug-in hybrid version of the new A3 that is capable of delivering an impressive 156 mpg.
Throughout his remarkable career at VW Group, supervisory board chairman Ferdinand Piëch has made a habit of setting seemingly impossible targets for his engineering teams. In 2001, he declared the production version of the Bugatti Veyron concept would have 1000 hp and would exceed 250 mph, even though no one at Wolfsburg knew whether problems with engine heat management, high-speed aerodynamics, and tire life could be solved. In 2007, Piëch bluntly stated VW would build a production car capable of an unbelievable 235 mpg by the end of the decade.
OK, so the XL1 engineers missed the launch date by a few years, but the XL1 is that car. And it's every bit as stunning an engineering achievement as is the mighty Veyron.
Improve Efficiency, Reduce Weight What Makes the XL1 a Mileage Master
Powertrain The XL1's compact hybrid powertrain is mid-mounted. It consists of a 47-hp, two-cylinder TDI engine with a compact 27-hp electric motor sandwiched between it and a bespoke seven-speed DSG automated manual transmission. Total system power output is 68 hp, but torque is limited to the maximum 103 lb-ft developed by the electric motor to preserve the transmission, which features an ultra-light gearset.
The all-aluminum diesel twin was developed from VW Group's 1.6-liter TDI four. Bore centers are 3.46 inches apart, with the bore measuring 3.18 inches and the stroke 3.17. The engine's piston and combustion chamber design is similar to that of the 1.6-liter. A crank-driven balance shaft helps smooth the vibration typically found in a parallel twin. VW claims the engine already exceeds forthcoming European emissions standards.
Lightweight Materials The XL1's monocoque chassis and exterior panels are of carbon-fiber-reinforced polymer using a resin transfer molding process that allows the parts to be made by an automated system, reducing production time, therefore increasing volume and reducing cost. The process involves effectively shaping the carbon pieces in heated and vacuum-sealed tools, then injecting liquid resin under high pressure. The pieces cure in the mold.
The body, including the doors and the thin-glass windshield, weighs just 507 pounds. VW developed a special paint process that delivers a Class A exterior finish over the carbon-fiber exterior panels and weighs 50 percent less than a conventional paint job.
The powertrain and battery pack weigh just 500 pounds. The entire electrical system weighs 231. The wheels are magnesium and fitted with light, low-rolling-resistance tires (115/80 R15 front and 145/80 R15 rear). Many of the suspension parts are aluminum and bolt directly to the carbon-fiber monocoque. Even the rollbars are carbon fiber. Just 23.2 percent of the XL1's total mass -- 405 pounds -- is made of iron and steel components.