Porsche 911 Turbo

Business Jet Traveler » August 2008
In the car’s tail sits a 480-hp liquid-cooled 3.6-liter flat six embodying mo
Friday, August 1, 2008 - 5:00am

Aircraft and car builders over the years have mined the alphabet and assayed certain letters as precious metal-GT, R, S, X and Z come to mind-but one five-letter word still stands alone as the medal for power in a pint-size package.

Turbo.

It says that something with wings can leap tall mountains and run strong where the air is thin. Mounted on a suitably shapely and well-shod car (let's forget the badge ever adorned minivans and K cars), it says the boiler room is street-legal nuclear-something tempestuous, not to be messed with.



When it introduced the 911 Turbo in 1974 (1975 in the U.S.), Porsche flaunted the car's horsepower by giving it outrageously flared fenders and a whale-tail spoiler, beneath which it affixed that word. The first time I saw one was when squinting through goggles, astride my motorcycle in driving rain. As I came up on the menacing shape ahead, its wide, crouching tail slowly took form. I inched forward for a closer sighting but suddenly this rare creature was gone, lunging forward on massive back paws and disappearing into a cloud of spray, its exhaust bellow briefly piercing my helmet.

Even back then, the 911 Turbo's 260 hp and 256 lb-ft (only 234 hp and 246 lb-ft for the U.S. market) were modest by muscle-car standards, but they were a leap from the naturally aspirated 911's 157 hp and 166 lb-ft in the U.S. at the time.



One of the problems to be overcome with a turbocharged car is the throttle response lag and the abruptness and uncontrollability with which the boost kicks in once the turbocharger's exhaust-driven impeller gets up to speed and packs air into the cylinders. With its rear-mounted engine, the early 911 Turbo earned infamy for this trait when pointed in other than a straight line. Engineers addressed another drawback (the law of physics that raises the temperature of air as it is compressed) by adopting an induction-air intercooler that lowered the Celsius but raised the complexity along with the power. The 911 Turbo first got an intercooler in 1978, taking the U.S. model to 265 hp and 291 lb-ft.



Aircraft reciprocating engines peaked with the "turbo compound" radials that powered the last Constellations and DC-7s. They squeezed every last joule of energy from each droplet of 145-octane gasoline by not only boosting the induction air but by harnessing the remaining exhaust gas flow to turn "power recovery turbines" connected to the crankshaft. Mercifully for aviation progress, the jet engine rendered these complex and cantankerous engines obsolete by the late 1950s.



Mechanical Advances

A modern, well-engineered turbocharged car bears about as much resemblance to the early ones as a jet does to a radial. Suck-squeeze-bang-blow is about all they have in common. The 911 has benefited from some clever mechanical advances and electronic-stability-augmentation systems over the decades that separate the squirrelly early 911 Turbo from the one shown on these pages. The inverted bathtub shape is still there, but it has been in turn eroded smooth and embellished over the years.



The erosion bestowed flowing lines on the car into the 80s and 90s, but the embellishment process is nowhere more evident than on the current 911 Turbo, with its display of gills, scoops, louvers and eyeballs from snout to tail. Granted, the Turbo has always been obliged to look the part, but the options for distinctiveness have become scarcer as the more pedestrian Porsches have gradually adopted the visual exaggerations introduced by the first Turbo. In the eye of this beholder, the lowlier current 911s look purer Porsche than the Turbo.



But I had no quibble with the drivability of the new 911 Turbo. Some manufacturers have adopted twin turbochargers of differing size to introduce boost more controllably and address the issue of lag and surge. For its latest 911, Porsche has given variable geometry to the turbines of two similarly sized, small turbochargers.



The new 911 Turbo is the first to offer this variable turbine geometry, the first with actively controlled all-wheel drive and the first to reach 60 mph in less than four seconds. Its engine offers 480 hp at 6000 rpm, and 460 lb-ft of torque from 1950 rpm to 5000 rpm with no dropoff. Aluminum doors and trunk lid shave 11 pounds of weight, giving the Coupe a power loading of 7.28 lbs/hp and zero-to-60 mph time of 3.7 seconds, and the Cabriolet 7.6 lbs/hp and 3.8 seconds. (Both times are for the six-speed, three-pedal manual gearbox on the Cabriolet tested.) The Tiptronic S transmission shaves 0.3 seconds off each time, but I'll take the notably sweet-shifting manual every time, thank you.



At low engine speeds, the low mass of a small turbine allows it to accelerate more quickly; a large turbocharger excels at higher engine speeds by creating less backpressure, but it's slower to spin up initially, creating lag. By adjusting the turbine vanes inside each of the engine's twin turbochargers, the Porsche variable turbine geometry creates the optimal profile as engine speed rises or falls. The benefits include higher torque at low rpms, more top-end power and strong torque over a broader range of rpms.



The Cabriolet tested for this article came with plenty of options, including ceramic brakes and the Sport Chrono Package. In addition to a glareshield-mounted stopwatch, the latter option features an overboost function that provides up to 45 lb-ft of extra torque under acceleration and adjusts the electronic throttle map for more dynamic response to pedal inputs. Sport mode also raises the trigger threshold for stability management and activates a stiffer suspension mode for faster turn-in and better road contact.



Enduring Mystique

Other than briefly driving a friend's new 911 Coupe in California last year, my time with this 911 Turbo Cabriolet was my first chance to get to know what it is about a Porsche that has given the marque such an enduring mystique. In a word, I would say it is the car's "Germanness" that is so appealing. This is a terrific automobile for everyday life, at once fierce and docile. Everything functions with a precision and tautness bordering on perfection, from the light touch on the steering, brakes, clutch and stick to the quick and distinctly un-turbo-like throttle response that begins each intense shove in the back.



The engine lacks the passionate voice of an eight- or 12-cylinder Italian, but its six horizontally opposed pistons make sweet, sweet music. Anyone with time behind the Continental IO-550 of a Beech Bonanza will hear that familiar flat-six soundtrack, but in the Porsche it is a more complex harmony in a higher key, with a brassy but muted treble to contrast with the deeper airplane sounds. The noise of the engine mimics the precision that this classically Teutonic, obsessively crafted car exudes. You have to drive one to "get" what a Porsche is all about.



Now, 34 years after watching that 911 Turbo vanish into the spray on a wet country road, I know why I knew that guy was driving a particularly fine motor car.

 

 

PORSCHE 911 TURBO CABRIOLET

 

Engine: flat six, 3.6 liters, turbo-charged, 24 valves



Engine output: 480 hp @ 6000 rpm; 460 lb-ft @ 1950-5000 rpm



Transmission: six-speed manual (on test car) or Tiptronic S



Weight: curb, 3,649 lb



Power loading: 7.6 lb/hp



Drag cd: 0.31



Top speed: 193 mph



Zero to 60 mph: 3.8 sec (manual) 3.5 sec (Tiptronic S)



Fuel capacity: 17.7 gals



City/highway (EPA): 15/24 mpg



Test average: 16.7 mpg



Standard retail price (2008): $136,500



Price as tested (2008): $154,050

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