WHEN a troupe of Porsche engineers arrived here on a Monday afternoon early this month, the flamboyant graphic designs covering their cars -- prototypes of the 918 Spyder, a supercar that is more than a year from its market debut -- barely distracted tourists from their preoccupations. Instead of stopping the show, the two otherworldly supercars slipped unobtrusively into a hotel driveway.
The engineers were jubilant: a two-week shakedown run, which started in Denver and proceeded through Phoenix on a meandering, blazing-hot route to San Francisco, revealed nothing to imperil the 918 Spyder's scheduled production start-up of Sept. 18, 2013.
A plug-in hybrid that combines electric drive and a midmounted gasoline V-8, the 918 Spyder is capable of highly efficient travel (when relying exclusively on battery power) or heroic feats (when the gas and electric power plants fully combine for 795 horsepower). Only 918 examples will be made; delivery to United States customers who have made a $200,000 deposit begins in January 2014, with each car priced at $854,000, not including shipping.
While Porsche is experienced in creating ultrafast cars and knows its way around hybrid powertrains and the production of carbon-fiber chassis, the 918's complexity presents new challenges. The Western road test was intended to verify hot-weather performance, which was reported as satisfactory. The project director, Frank Walliser, and his colleagues also worked on harmonizing the car's myriad systems. The engineers looked for hiccups in drivability that would signal a need for further development of the car's software.
"The biggest job today is the integration of the car," Mr. Walliser, 43, said during a ride-along session held later that 97-degree afternoon in the Beehives section of the Valley of Fire State Park, northeast of here. The park's landscape of odd sandstone formations, eroded in the 150 million years since the Jurassic period, provided a contrasting setting for the futuristic Porsche. Against a low sun, with the rocks changing hues to sometimes match Mr. Walliser's orange T-shirt, it seemed as if a John Ford western might break out.
Those who found the 918 Spyder design study so mesmerizing when it was introduced at the 2010 Geneva Motor Show would not be disappointed with the prototypes. Spattered and smudged from the journey up and down mountains and across searing basins, the cars closely resembled that sparkling concept. Key aspects that remain true include the huge wheels, 20 inches in front and 21 inches at the rear, and a signature swooping line that starts just behind each front wheel. The line continues rearward, opening up to intake scoops that supply radiators, one on each side, that cool the midmounted powertrain.
The 918 Spyder has removable roof panels, similar to those of past 911 Targa models. The roof's pronounced "double-bubble" contours draw straight into a similarly undulant rear cowling. The Geneva car's electric-lime exterior and interior accents survive. And by standing directly in back and staring, as an early critic observed, you can still see the face of Donald Duck.
Evolving to meet practical considerations like crashworthiness, the 918 Spyder has grown by six inches, to an overall length of roughly 183 inches. The gasoline engine has expanded, to 4.6 liters (580 horsepower) from the concept car's 3.4 liters. There are three electric motors, one at each front corner and a third integrated with the engine and transmission.
A 7-speed dual-clutch automatic transmission regulates all this might. To lower the car's center of gravity, the transmission has been flipped upside down, placing the weighty gear clusters closer to the road.
One notable change from the concept car is the deletion of exhaust pipes that emerged through the bodywork just ahead of each rear wheel. Hot gases now exit upward through the rear cowl, with the two pipes looking like ship's funnels.
"The temperature problem in back is very challenging," a powertrain engineer, Christian Hauck, said. "We decided to get the heat as soon as possible out of the back."
According to Mr. Walliser, the project is on target to meet its three main goals, which include delivering an evocative design, excelling at hotlaps around the Nürburgring and realizing a fuel economy equivalent of 70 m.p.g. when the car runs in electric mode. (As an E.V., it can go up to 15 miles on power from the 6.8-kilowatt-hour lithium-ion battery with a top speed of 90 m.p.h.)
Glancing through the windshield at the square-crowned fenders and the desert shrubs beyond, I buckled into the passenger seat as Mr. Walliser demonstrated the small knob on the steering wheel used to select the driving mode settings: electric, hybrid, sport and race. He took off forcefully with the car in its electric mode; aside from the lack of a clanging bell, it sounded and felt like an old-fashioned streetcar, grumpily urging us forward.
Hybrid mode wakes the gas engine for variable assist between the two systems. Sport mode, with added assistance from the electric drive, knocked off my hat as I shot backward against the headrest. Race-mode acceleration was something else entirely, with all the raucous sounds of a cattle drive compressed into three surf-guitar seconds -- about how long it takes to go from 0 to 60 m.p.h. Abrupt crests and random whoop-de-dos on the park road did not flummox the suspension.
But because of the dusty interior and the swarm of cables and electrical boxes, I kept thinking of the 918 Spyder prototype as a kit car instead of the state-of-the-art machine that will cost as much as four Bentley Continental GTs with enough left over to buy a Panamera S. Undoubtedly, this perception will recede as the 918 takes on its final polished form.
Putting aside these subjective responses, though, questions linger about Porsche's special sports car. Foremost is the daunting task of finishing development work in less than a year. Both prototypes balked at times, and the gray one was momentarily stilled at the side of the road during one ride-along. The second question is about the necessity of the hybrid electric drive system. Are the benefits really worth the cost and complication?
Once it's removed from the gaudy surroundings of the Las Vegas Strip, though, the 918 Spyder showed incomparable zing. Michael Hölscher, project manager for research at Porsche, said people had reacted generously throughout the team's journey.
"I've never had such positive feedback," Mr. Hölscher said. "Everybody's happy we made the car. I think we did the right thing."
This article originally appeared in The New York Times.