STUTTGART, Germany (AP) -- Porsches are known for the sound of their rippling horsepower under the hood, but the company's new gas-saving hybrid actually runs on batteries more than half the time -- leaving the driver with little more than the sound of the wheels on the road.
Using a parallel full hybrid design developed with Volkswagen and Audi engineers, the prototype Cayenne S Hybrid relies on a combination of internal combustion and electric power to reduce C02 emissions and boost mileage from 14 mpg in the city to 24 mpg.
That's still only half what the Toyota Prius hybrid gets, but then again, it's an SUV. The company wants to improve mileage further by the time the Cayenne S Hybrid hits the market in 2010.
While many other hybrids deliver their benefits primarily in city traffic, the Cayenne S Hybrid allows drivers to cruise at up to 86 mph (138 kph) on the highway using electric power alone. If that's a little slow for you, put the pedal down, the combustion engine comes alive again, and off you go.
That's key for the designers of the new Cayenne. While it's not the first hybrid -- or even the first hybrid SUV -- coming to the market, it's the first Porsche hybrid and the company has been very careful to retain the performance that its customers expect.
Porsche touts it as delivering the "power of a V8 and the efficiency of a four-cylinder."
"The Cayenne Hybrid is a special driving experience," said Michael Leiters, project manager of the Cayenne product line, after a recent test drive in and around Porsche's hometown of Stuttgart.
"It can be completely electric or use the engine at the same time to improve acceleration -- there is also what we call 'sailing,' or coasting with the engine off at speeds up to 86 mph, when the driver can only hear the wind."
It's not an idle boast: On a recent test drive for reporters, one passenger remarked on the hum of the electric motor as the Cayenne whizzed down the road, but the noise turned out to be coming from the radio, which wasn't properly turned in to a station. After it was shut off -- silence.
So far, fuel consumption is not as good as the more conventional diesel version of the Cayenne, making its debut at this week's Geneva Auto Show. But Porsche is working on the hybrid primarily for the U.S. market, where diesels are not as popular, said Klaus-Gerhard Wolpert, director of the Cayenne Product Line for Porsche.
"At the moment diesel is the European answer because of lower taxation and pro-diesel legislation, but the market in the U.S. for hybrids is better," Wolpert said.
Research anticipates overall hybrid sales in the U.S. more than doubling by 2014 to 743,000 vehicles per year, Wolpert said.
More stringent European Union C02 emissions standards coming into place by 2015, and new fuel consumption regulations for the U.S. by 2020 -- not to mention a likely increase in oil prices -- are also expected to help boost the hybrid market worldwide.
The Cayenne S Hybrid relies on a supercharged Audi 3.0-liter V6 engine, which produces 333 horsepower. It is paired with a 52 horsepower three-phase synchronous electric motor that also acts as an alternator, and both are joined to an eight-speed automatic transmission.
Top speed comes in sixth gear, while the two higher gears help reduce engine speed and enhance fuel economy.
It's in eighth that the driver can "coast" at 86 mph along the highway.
So far, city test drives have shown that the vehicle uses the gasoline engine 44 percent of the time. The rest of the time, the engine is boosted with the electric motor or is turned off entirely, relying only on electric power.
Sitting at a traffic light or in a jam? The combustion engine goes off.
As you brake, the kinetic energy is converted into electrical energy to help recharge the battery.
When the battery storage level is less than 18 percent, the combustion engine restarts so that the battery never runs out of power.
"Everyone was skeptical that we could do it -- that we could stop and restart the engine without the driver feeling it," Leiters said.
But the transition is smooth. Otherwise the design is the same as the gasoline version, with the nickel metal hydride battery tucked away under the luggage compartment.