On the automotive spectrum, Porsche and Prius are poles apart. For decades, one was the definitive German high-performance sports car brand, renowned for its extreme engineering and screaming flat-six engines. The other is barely a decade old, the very image of the modern high-mileage hybrid.

Now the spectrum has warped, and the poles are coming closer. The Cayenne S Hybrid is about as far away from the earnest nerdiness of the Prius as any Porsche can get. Porsche had first discussed a hybrid Cayenne in 2005; the first functioning version appeared at the Los Angeles Auto Show in November 2007.

The 2011 Porsche Cayenne S Hybrid uses a direct-injected, supercharged Audi 3.0-liter V6 engine rated at 333 horsepower, paired with an eight-speed automatic transmission. Between the two is mounted a 38-kilowatt (52-hp) electric motor that puts out 221 lb-ft of torque, a full two-thirds as much as the engine itself does.

“Sailing on Electricity”

The system’s unique feature is a hydraulic clutch between the engine and motor that disengages the engine so it can shut down under light loads. The electric motor then takes up the load until the engine restarts. Porsche engineers call the result “sailing”—for the quiet sensation of speed using only electric power.

As in most hybrids, the electric motor also restarts the engine, and recharges the battery pack (believed to contain 1.2 kilowatt-hours of energy). Fitted into the former spare-tire well, the pack uses Sanyo nickel-metal-hydride cells (as do the Ford Escape Hybrid and Ford Fusion Hybrid). This is a simpler and less costly system than Toyota’s Hybrid Synergy Drive, but it comes with drawbacks, one being that the vehicle can’t use the engine to recharge the batteries while running on electric power at the same time.

Porsche’s hybrid system is tuned to give lots of electric assist at highway speeds. This makes sense, since the large, heavy, tall SUV isn’t an ideal urban car, and may spend less time in city traffic than other hybrids.

Illegal All-Electric Speed!

Porsche says the Cayenne S Hybrid runs up to 1.2 miles in all-electric mode. More remarkably, the company also says it can run on electricity at speeds up to 86 miles per hour—though that’s slightly deceptive, since it means the engine may shut down for a while at speeds that high, leaving the electric motor to propel the car. Still, traveling on battery power at speeds higher than any legal US limit is quite an accomplishment for a 5,000-pound SUV.

As for on-road performance, the company claims 0 to 62 mph in 6.8 seconds with both the electric motor and the boosted engine providing power. At the same time, the fuel economy ratings of 20 in the city and 23 on the highway are a big improvement over the 2010 Cayenne S figures of 13 city and 19 highway mpg (with a much larger 4.8-liter V8).

Porsche for Russia and China

First sold in 2003, the Cayenne gave Porsche an entry in the burgeoning luxury-SUV segment—as well as a vehicle to sell to the newly wealthy in countries like China and Russia, where substandard roads made driving its low-slung sports cars problematic. The Porsche truck shared a basic platform with the Volkswagen Touareg and Audi Q7, but used unique styling and heavily reworked powertrains and suspension.

Most Cayenne Hybrids are likely to be sold in North America, where hybrids take a greater share of sales than any other market. Mileage-minded Europeans are likely to opt for the 3.0-liter V6 diesel Cayenne that will debut at the Geneva Motor Show in March 2009. That vehicle, however, will not cross the ocean.

Porsche will use the same system in a hybrid version of its upcoming Panamera four-door sedan.

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