Test-Driving Porsche 911 Turbo Cabriolet: 480 Horsepower

Sept. 10 -- STUTTGART, Germany -- Dawn is breaking as I turn onto the autobahn south of Stuttgart behind the wheel of Porsche's new 911 Turbo Cabriolet, which has just gone on sale in the United States.

I hit the gas, and in less than four seconds, I've blasted from standstill to more than 62 mph -- something you'd normally need a sports motorcycle to do.

In about 13 seconds, I'm racing at over 125 mph -- and then I realize I'm only in fourth gear. A few seconds later, I'm briefly cruising at about 170 mph in fifth gear, with plenty of room to go before reaching the max speed of 192 mph. However, one emotion prevents me from taking the car up to the sixth and highest gear: fear.

I'm too scared to put the Porsche into top gear, even though I'm on a half-mile stretch of straight autobahn and in complete control of the car. But then again, I'm going as fast as a jet taking off from a runway.

As I grip the steering wheel, passing more cars than I'd expected to meet at daybreak, I'm concentrating too hard to think about the automated gadgetry that makes this high-thrill driving possible.

The new Cabriolet Turbo is not merely a convertible version of the 911 coupe, some hardtop with the roof sawed off. Added are electronic sensors and an aerodynamic design that couple better handling with power.

This reddish color might not be everybody's favorite, but the TomTom GPS (an after-market extra) would come in handy for most drivers.

As I steam along, the electronics are hard at work. The car feels as if it were gripped to the pavement by train tracks, giving me the freedom to choose the trajectory I want, when I want.

At 8:30 a.m., when traffic becomes too thick for (reasonably) safe high-speed driving, I slow down to 125 mph.

Its time to listen to some music. I wonder, though, how this will be possible at such a high speed. Already, its very loud, and with a passenger in tow, it's difficult to talk without shouting.

Somehow, though, I can hear the words of Rush’s Red Barchettaover the sound of the motor, as the wind blows my hair back like a horizontal buzz cut.

The Bose sound system makes this possible by piping the music through 12 loudspeakers and a seven-channel digital amplifier. Unlike the coupe version of the 911 in which the sounds come from the back, the speakers are positioned closer to the front, along the foot well.

To better gauge the 911’s electronic controls, I leave the autobahn for a smaller highway that winds through a forest. It has just rained, and the pavement is wet.

Accelerating out of a curve at 60 mph in second gear, I accidentally pop the clutch. A massive jolt blasts me forward. The acceleration is way faster than I expect.

Instantly, the Porsche's electronic stability-control system transparently takes over. But it's almost too fast. I instinctively start to countersteer to adjust for the sliding back end of the car, but the car has already righted the front-wheel traction to compensate for the lateral motion.

The 3.6-liter engine relies on a variable-geometry, turbocharged engine to crank up to 480 horsepower and a top speed of 192 mph, with an average Porsche-specified gas consumption of about 22 mpg.

To get you out of trouble, the Porsche's computer and sensor systems perform thousands of computing tasks in milliseconds.

The traction-management system prevents the tires from skidding. A stability-management system distributes torque between the all-wheel-drive Cabriolet’s front and rear axles. If the wheels in the back begin to lose traction on a wet surface, the system feeds more torque and power to the front axle.

For speed freaks who want to experience what Porsche calls the “lateral dynamics on the race track� – i.e., skidding -- the stability-control system can be deactivated with a button on the dashboard. However, even then, the traction control is reactivated as soon as the brake is stepped on.

But the engine’s power is the real attraction of this car. All told, the Cabriolet packs 480 horsepower at 6,000 rpm and 457 pound feet of torque. With the Sports Chrono Package Turbo, torque is further extended to 501 pound feet.

Like an overclocked PC, the 911 Turbo Cabriolet’s engine emits a huge amount of thermal energy in a confined space.

Temperatures inside the cabriolet’s variable-turbine geometry engine approach 1,000 degrees Celsius. For the engine to handle such extreme temperatures, Porsche says it has tweaked it material composites for enhanced heat resistance, while bolstering radiator cooling with a combination water- and air-cooling system. At speeds of 186 mph, the air-intake vents feed about 4,000 liters of air per second through the heat exchangers for the radiator. Engineers have housed a fan directly above the engine in the back for additional active cooling.

As a measure of Porsche’s engine-design progress, the first-generation 911 Turbo Cabriolet, released in 1987, had a 3.3-liter engine that achieved 300 horsepower, which was then considered a magic benchmark. It had a top speed of 161 mph; and stop-to-62 mph acceleration was 5.4 seconds.

Twenty years on, the new Cabriolet has a slightly larger 3.6-liter engine that can crank up to 480 horsepower, zooming the car at a top speed of 193-mph. According to Porsche, it gets about 22 miles to the gallon.

But for Porsche lovers that want even more power, the firm is on track to bring its fastest 911 yet, the GT2, to the United States early next year. The 911 GT2's 3.6-liter boxer engine will offer maximum output of 530 horsepower -- zero-to-60 mph acceleration in 3.6 seconds and a top track speed of 204 mph.

Of course, all this power has its cost. The 911 Turbo Cabriolet retails for $136,500, and the GT2 will cost a cool $191,700. Already, Porsche’s engineers are at work on the design of an even-more-powerful 911 for launch in the next few years.