Contents

• Highlights
• 911 Carrera 4 Setting a New Standard in Sporting Safety
• Technical Features Perfect Four-Wheel Drive for a Sports Car
• Engine Technology A Boxer with a Bright Future
• PSM Extra Driving Safety All-Round
• Market Position First Class Business Express
• History Almost 100 Years of Porsche Four-Wheel Drive
• Technical Details Specifications

Highlights

Permanent Four-Wheel Drive with Perfect Power Division

Benefitting from years of thorough experience with four-wheel drive systems, Porsche's engineers have found a particularly effective solution with the Carrera 4: Variable distribution of drive forces to the front axle via a viscous clutch in the front differential guarantees excellent traction and supreme driving safety on all kinds of roads and under all weather conditions.

Porsche Stability Management

The Carrera 4 is the first Porsche ever to feature PSM Porsche Stability Management, a highly sophisticated dynamic control concept serving to stabilise the car in an extreme situation by intervening in the engine management and brake system. Offering supreme stability in this way both in longitudinal and crosswise direction, PSM has been specially tuned to the typical requirements of a Porsche and the Porsche driver, ensuring that the sporting character of the car is not suppressed by premature intervention. The objective in this tuning process was therefore to offer brief but decisive driver support in conjunction with the four drive wheels whenever the car suddenly comes too close to the limits of physics.

Electronic Gas Pedal

A gas pedal incorporating a sensor to transmit electrical signals to the Motronic and an actuator operating the throttle butterfly are the essential features required for dynamic drive control with all the qualities of Porsche Stability Management. The use of such sophisticated electronics pays off not only in extreme situations, since E-Gas, as it is called, also improves the response of the engine to the accelerator and allows a further reduction of fuel consumption by adjusting the throttle butterfly perfectly to the engine control map. A further advantage is the reduction of exhaust emissions and last but not least E-Gas also provides even better cruise control.

Large-Volume Side Airbags Fitted as Standard

Apart from the full-size frontal airbags for the driver and front passenger, Porsche's new and highly progressive Side Impact Protection System (POSIP) comes as a standard feature. It consists of two side airbags fitted in the doors and additional door lining taking up impact energy. Offering extra-large volume of no less than 30 litres, the two side airbags ensure optimum efficiency throughout the entire seat adjustment range, POSIP thus protecting the driver and his front passenger in all areas around their head, chest, arms and hips, even with the roof down and the side windows fully retracted.

Another Porsche First: Four-Wheel Drive plus Automatic Transmission

The new Carrera 4 is the first-ever Porsche allowing the customer to combine four-wheel drive both with a six-speed manual gearbox and five-speed Tiptronic S.

Exclusive Aluminium Wheels for the Carrera 4

A clear sign of distinction characterising the Porsche 911 Carrera 4 at very first sight is provided by the 17-inch light-alloy wheels in unmistakable spoke design. Extending far inside to the hub, the spokes become wider towards the rim and merge into the base at the far outside, making the wheels look even more powerful and larger.

Discreet Signs of Distinction

Applying the principle of being "great to look at but even greater inside", the Carrera 4 does not in any way flaunt its wares. The Carrera 4 model designation stands out in titanium colour on the engine compartment lid and is also to be admired on the black wheel hub covers. Further visible signs of distinction are the special 17-inch wheels and titanium-coloured brake callipers. Like all Porsche 911s in the 1999 model year, the Carrera 4 comes furthermore with modified headlight units, the direction indicators in the headlights and the side indicators now coming in white, while in the rear light clusters they are whitish grey and no longer orange.

Superior Driving Safety, Outstanding Driving Qualities

The springs, anti-roll bars and dampers are all specially tuned and modified to reflect the dynamic driving qualities of the four-wheel-drive model. Consistent adjustment of axle geometry to four-wheel drive and re-tuned elasticity on the front axle ensure neutral behaviour all the way to extreme limits, allowing the driver to safely approach the highest possible speeds in a bend without losing control of his car.

Superior Crash Safety

Carefully defined deformation of the steel bodyshell keeps the loads acting on the car's occupants in an accident to an absolute minimum. Throughout the entire process of developing the new Carrera, passive safety was consistently enhanced to an ever-increasing standard, the results of numerous crash tests confirming the conviction of Porsche's engineers that they have created one of the safest high-performance sports cars in the world.

Air Drag and Lift Forces Reduced to a Minimum

The Porsche 911 offers a low drag coefficient compared with other sports cars. And at 0.58 m2, the product of drag coefficient and the frontal area of the car is also very low and therefore advantageous on the road. A further, particularly important factor is the minimisation of lift forces on the 911 Carrera, the Cfalift factor on the front axle being a mere 0.08, while rear axle lift, thanks to the spoiler automatically coming out at speed, is even lower at 0.05.

Water-Cooled Boxer Engine

An efficient cylinder charge ensured by four-valve technology and stable thermal conditions guaranteed by water cooling make Porsche's flat-six power unit a genuine performance machine. Displacing 3.4 litres, the engine of the 911 Carrera 4 develops maximum output of 300 bhp or 221 kW. Top speed is 280 km/h or 174 mph. A further point is that the horizontally-opposed engine, through its concept alone, offers decisive benefits in the construction of a sports car: Compensation of mass forces is perfect, dimensions are kept to a minimum, and the short, stiff crankshaft allows high engine speeds.

Aluminium Suspension

All track control arms on the suspension and the two axle subframes integrated in the body are made of light alloy. In its design and dynamic driving characteristics, the front axle has been modified in accordance with the car's four-wheel drive technology.

Four-Piston Monobloc Brake Callipers

Following positive experience in motor racing, the Porsche 911 Carrera 4, like all other Porsche models, comes with four-piston monobloc brake callipers made of light alloy. A particular advantage of this technology is the high standard of safety ensured at all times and minimum fading even under extreme conditions.

Litronic Headlights with Dynamic Range Control

The 911 Carrera 4 is available as an option with Litronic headlights, special gas-discharge units illuminating the road ahead far more brightly and thoroughly and thus significantly improving safety at night. A further contribution to your extra driving safety is the dynamic headlight range control considering not only the load the vehicle is carrying, but also any change in body angle (sway) due to dynamic driving conditions. The halogen bulbs (H7) for the high-beam headlights are surrounded by a particularly efficient free-space reflector. Whenever the driver activates the high beams, the low-beam headlights remain switched on and also move their own beam up by way of headlight range control in order to improve illumination of the road ahead. A further feature of the Litronic headlights, finally, is the headlight cleaning system.

Individual Sports Features

It almost goes without saying that the Carrera 4 can be enhanced to an even more sporting standard as an expression of the customer's personal taste. Features available individually are sports seats with reinforced side support, 18-inch turbo-look wheels measuring 225/40 ZR 18 at the front and 265/35 ZR 18 at the rear, and – as on the coupé – a sports suspension with even firmer and shorter springs, harder dampers and reinforced anti-roll bars.

The Four-Wheel-Drive Porsche 911

Setting a New Standard in Sporting Safety

The Carrera 4 continues the tradition of four-wheel-drive 911 models dating all the way back to the Porsche 959. Production of the new car will be starting in October 1998, the Carrera 4 being available from the start in both coupé and cabriolet guise either with a six-speed manual gearbox or, as an alternative, with five-speed Tiptronic S.

Permanent four-wheel drive with variable power feed to the front axle is provided by a viscous clutch taking the former system to an even higher level of development. Power is delivered to the front wheels on the new model no longer by the conventional transaxle system running in a separate tube, but rather by a low-weight drive shaft in the central tunnel. The viscous clutch, in turn, has been moved from the gearbox into the front differential housing for better weight distribution.

The Carrera 4 emphasizes its particularly high standard of technical excellence not only through permanent four-wheel drive, but also through PSM Porsche Stability Management featured in this car for the first time. The particular advantage of PSM is that it combines existing longitudinal control systems, such as anti-lock brakes, anti-spin control and the Automatic Brake Differential (ABD), with dynamic lateral control tailored specifically to four-wheel drive. Brake intervention and automatic engine power control without the driver having to intervene himself serve to keep the car stable also in bends. Oversteering is avoided by automatically applying the brake on the outer front wheel in a bend, understeering (with the car "pushing" the front wheels) is eliminated by applying the brake on the inner rear wheel.

Front Axle Modifications

In its body design, the Carrera 4 has been modified at the front to accommodate the additional drive units. Further modifications were required in the area of the front axle and on the redesigned fuel tank still offering almost exactly the same capacity as before. The emergency wheel is replaced by an even more compact folding wheel, the luggage compartment offering a capacity of no less than 100 litres or 3.5 cu ft, despite all the comprehensive modifications and changes mentioned.

Like the existing models, the new Carrera 4 is powered by Porsche's six-cylinder water-cooled boxer now entering its third year of production. Engine displacement of 3.4 litres, maximum output of 300 bhp (221 kW) at 6800 rpm, and maximum torque of 350 Nm (258 lb-ft) at 4600 rpm remain unchanged. Top speed of the coupé model is 280 km/h or 174 mph.

The most significant modification on the engine is the throttle butterfly now operated by an actuator, an electronic gas pedal instead of the conventional mechanical connection serving to give gas. Further advantages of this innovative technology are even better engine response, low exhaust emissions and a further reduction in fuel consumption.

Less Weight, Better Weight Distribution

Permanent four-wheel drive on the new Carrera 4 feeds most of the engine's drive power from the gearbox straight to the rear differential. The amount of drive power fed to the front axle, in turn, is a function of rear-wheel slip and is controlled by a viscous clutch. Accordingly, the share in engine power fed to the front wheels varies from 5-40 per cent.

Drive power to the front wheels no longer goes through a separate tube according to the transaxle principle, as on the former model, but rather flows through a drive shaft in the frame tunnel. The viscous clutch is now housed within the front axle differential, the advantages of these modifications being a reduction in weight, an improvement of weight distribution and the option to combine four-wheel drive with either a manual or Tiptronic gearbox without any significant modification of the main gearbox units.

With the entire concept of the Carrera 4 figuring into the development of Porsche's new model generation from an early point, only minor modifications to the suspension were required for the addition of four-wheel drive: The front axle features modified wheel bearings and the springs, dampers and anti-roll bars have all been adjusted to the dynamic driving qualities of the four-wheel-drive model.

The driving characteristics of the new Carrera 4 follow Porsche's proven concept, the car retaining the character of a genuine Porsche with its accurate and very agile steering behaviour in bends, despite four-wheel drive. The specific advantages of the more sophisticated drive system in everyday motoring are the even more stable directional stability at high speeds, reduced sensitivity to cross-winds, and far better traction at all times.

Substantial modifications were required at the front end of the car in order to provide space for the differential and drive shafts. One of these modifications is the change in tank design, while tank capacity remains virtually unchanged. And while the front luggage compartment complete with a folding wheel on the floor of the Carrera 4 has become a little smaller, it still offers 100 litres or 3.5 cu ft of luggage space.

New Wheel Design

Seen from outside, the new Carrera 4 bears only a few external signs of distinction. Like all models in the 1999 911 model range, it comes with white direction indicators at the front, side and rear (side indicators dropped on the US models). The Carrera 4 model designation and the brake callipers stand out clearly in titanium colour, but the most striking feature is the 17-inch wheels specially designed for the Carrera 4, which is incidentally also available with 18-inch wheels in turbo look.

Other sporting extras such as sports seats or – on the coupé – a sports suspension with shorter and firmer springs, reinforced anti-roll bars and firmer gas-pressure shock absorbers are of course available to the customer on individual order.

The wide range of additional features and special equipment already available for the two-wheel drive Porsche 911 is likewise available in full on the Carrera 4.

Technical Features of the New Model

Perfect Four-Wheel Drive for a Sports Car

The Carrera 4 continues the successful tradition of four-wheel-drive Porsche 911 models. Its drive technology is a further development of Porsche's proven and highly successful concept, the entire process of developing the new Carrara 4 once again confirming the experience that the best way to divide power between the two axles on a rear-engined sports car is with a viscous clutch.

A viscous clutch is a fully encapsulated multiple-plate unit filled with highly viscous silicon fluid. Part of this multiple-plate clutch unit is connected directly to the rear-wheel drive, the other section is connected with the front axle. Whenever wheel slip results in a difference in speed between the axles there is also slip between the plates within the viscous clutch. In that case, depending on the degree of slip, drive power is transmitted to the front axle by the viscous silicon fluid.

Short Propeller Shaft Within the Frame Tunnel

A number of fundamental modifications have been introduced between the gearbox and the front axle in the process of changing over to the new model:

The first point is that the drive shaft no longer runs through a rigid tube as with the transaxle principle. Instead, the new Carrera 4 features a short propeller shaft running freely within the frame tunnel. The first advantage is that this solution is about 4 kilos lighter, the second point is that it provides space for the coolant pipes now running through the tunnel for the water-cooled flat-six power unit.

Yet a further point is that the viscous clutch is no longer within the transmission itself, as it was in the past. Rather, it is now housed on the 911 Carrera 4 in the front differential casing moved far back to the rear of the car, a modification offering the big advantage that the larger differential housing and the viscous clutch apply a bit more weight on the front drive axle. This means even better front-to-rear weight distribution beneficial to the car's driving characteristics and traction.

Four-wheel drive on the new Carrera 4 ensures that a certain amount of torque is always able to flow to the front wheels at all times. This share of power conveyed to the front varies from 5-40 per cent, depending directly on drive slip on the rear wheels.

Driving Behaviour Even Better Than Before

The primary objective in this case is of course to perfect the characteristic driving behaviour and the superior driving safety of the Porsche 911, thus reaching a higher standard than ever before. Four-wheel drive conveys the supreme power of the engine to the road even more smoothly and steadily than one drive axle.

Installing four-wheel drive in the floor pan of the Porsche 911 required a number of modifications.

The first point is that various body components had to be modified in the region of the front axle in order to accommodate the front differential. This called for a new fuel tank shaped like a saddle and offering approximately the same volume as before. An inevitable result of the more sophisticated drive technology is a slight loss of space in the luggage compartment, which is however kept to a minimum by the folding wheel in flat arrangement on the floor. Luggage compartment capacity therefore remains adequate at 100 litres or 3.5 cu ft. And despite its more sophisticated technology the Carrera 4 remains a light and agile vehicle from the start, the coupé weighing in at 1375 kg or 3032 lb, which makes it only 55 kg or 121 lb heavier than its rear-wheel-drive Carrera counterpart.

Porsche Engine Technology

A Boxer with a Bright Future

The water-cooled six-cylinder power unit of the Porsche 911 Carrera 4 sets the standard in modern sports car engine technology.

"Our pledge to the six-cylinder boxer engine is more than just tradition", states Horst Marchart, Porsche's Member of the Board for Technical Development and the Managing Director of the Weissach Research and Development Centre. "Considering the sum total of its properties, the boxer engine is the ideal configuration for a six-cylinder sports car of the type we build."

Very low in design, the boxer engine is the ideal match for Porsche's two automobile concepts, the mid-engined Boxster and the rear-engined 911. With the pistons running in opposite directions, smoothness and refinement are enhanced to perfection. A six-cylinder horizontally-opposed power unit is entirely free of mass forces and mass momentum, the crankdrive is perfectly balanced. And this ensures not only top quality and behaviour in mechanical terms, but also allows a sports engine of this calibre to reach high engine speeds without the slightest problem.

Less Emissions

The changeover from air to water cooling was necessary in technical terms in order to master all the requirements of four-valve technology. Four valves per cylinder are indeed essential these days in order to combine superior power and performance with equally superior fuel economy and emission control.

Porsche's clear pledge to water cooling is also based on many years of practical experience. And this means not only the good features and qualities offered by Porsche's water-cooled production engines with both four and 8 cylinders. The TAG engine enabling McLaren to win the World Formula 1 Championship three times, for example, was a water-cooled V6 designed by Porsche. In GT racing, in turn, Porsche has been building water-cooled six-cylinder boxer engines ever since 1977, initiating an exemplary series of successes in motor racing that has continued throughout these 20 years to this very day. Engines of this kind are to be found in Porsche's Le Mans-winning cars and in the very latest 1998 911 GT1 which scored a one-two victory in this year's 24 Hours of Le Mans, marking Porsche's 16th triumph in this world-famous race.

The engine of the Carrera naturally differs significantly from these racing machines, reflecting Porsche's new principle of using shared parts: In their fundamental design and configuration, the power units of the Boxster and Carrera are basically identical. But in terms of size and output these two six-cylinders are clearly different, the Boxster displacing 2.5 litres and developing maximum output of 204 bhp (150 kW), while the 911 Carrera displaces 3.4 litres and develops maximum power of 300 bhp (221 kW).

Highlights in Technology

Through their configuration and the materials used, Porsche's new boxer engines stand out clearly as ultra-modern power units built for all the requirements of today and tomorrow. The two-piece crankcase separated down the middle is made of pressure-cast light-alloy. Offering very good surface quality, this material ensures perfect production of even very delicate parts and components, at the same time keeping the crankcase very light. And since this kind of pressure-casting is not suitable for the cylinders and their liners subject to the most demanding running conditions, the six cylinder liners are made of silicon alloy subsequently cast into the crankcase during the production process.

Built for Sporting Performance

A further speciality of the Porsche engine is the separate bearing bridge accommodating the crankshaft with its 7 main bearings as well as a layshaft. The aluminium block encompassing the central section of the crankdrive incorporates cast-steel support elements to give the bearings a strong and secure fit. On the Carrera engine revving up to a maximum speed of 7300 rpm, this component is reinforced to a far higher standard than on the Boxster engine where the speed limiter cuts in at 6700 rpm.

Featuring a large bore and short stroke, both engines are sporting and dynamic in their configuration, ensuring both superior refinement and the ability to run smoothly and reliably even at very high speeds. Bore on the engine of the Carrera 4 is 96 mm or 3.78", stroke measures 78 mm or 3.07".

The boxer engines of the Porsche Carrera models also differ from traditional design concepts in terms of their oil circuit. Taking up approximately 12 litres of oil, the "classic" dry sump lubrication on the engine of the 911 required a separate oil tank connected by pipes to the engine itself. Now the integrated dry sump lubrication keeps its oil reserve of approximately 10 litres in a chamber within the engine housing separated from the crankshaft area.

The next example of technical progress offered by the boxer engine is its cylinder heads: Each of the two cylinder heads houses two camshafts operating two inlet and two outlet valves per cylinder. This increase in the number of valves from two to four offers three advantages in particular:

• The overall cross-section opening of the four cylinders is obviously larger, facilitating the intake of fresh air and the expulsion of exhaust emissions. The positive results are an improved cylinder charge and an even more powerful, dynamic operating cycle.
• The individual valves are lighter in weight whenever four smaller valves replace two larger ones. The reduction in moving masses ensured in this way allows the four valves to open and close more precisely at high speeds.
• With the valves being arranged conveniently within the roof-shaped combustion chambers, there is ideal space for the spark plug right in the middle. And from here flame travel is the same in every direction. This, in turn, guarantees fast and thorough combustion, meaning lower fuel consumption and less harmful emissions.

Very Compact Design

The drive concept for the four camshafts introduced by Porsche adds yet another outstanding example to the Company's high standard of engine construction: From the crankshaft power first flows through a chain to the layshaft already mentioned. Featuring one pinion each at the front and rear end, the layshaft then drives two further chains leading to the outlet crankshafts. This displaced geometry saves space by using the displaced rows of cylinders left and right in order to accommodate the two chain boxes. It is indeed this particular design which, to a large extent, makes the water-cooled boxer 70 mm or 2.76" shorter than the air-cooled version on the previous model, even with the distance between cylinders remaining the same.

Featuring two camshafts and one camshaft adjuster, the current six-cylinder is able to vary intake valve timing by 25°. This is done via a hydraulic camshaft adjuster on the chain between the outlet and intake camshafts, this process of intervening in valve timing offering several advantages:

• The engine is able to idle more smoothly and consistently
• Torque and pulling force at low engine speeds are improved
• Both emissions and fuel consumption are further reduced to an even lower level
• As a particular feature each cylinder head comes with an oil extraction pump delivering reflow oil into the integrated dry sump

Thermal Reserves and Superior Efficiency

Whenever Porsche's engineers replace air cooling by water cooling, the new water cooling system must be a very good one. So to "refresh" the cylinders and combustion chambers they have chosen a principle otherwise to be found on racing engines: The flow of coolant is clearly separated on each side by the cylinder gasket. With the ducts being appropriately designed, this allows the temperature of the coolant to be adjusted perfectly to current requirements. The flow of coolant through the cylinder heads and along the cylinders themselves is not lengthwise, as is otherwise the case with production engines, but rather crosswise from the outlet to the intake side, again reflecting a technology well known from motor racing. Coolant then flows back through two separate longitudinal ducts, the big advantage of this system being that the cylinder heads and the cylinders themselves always receive the same, sufficient and consistent supply of coolant.

Water cooling ensures a good thermal balance also elsewhere, both the coolant itself and the engine oil flowing through a heat exchanger. With the coolant reaching its operating temperature relatively quickly, it is able to initially warm up the engine oil almost immediately after the engine has started. And then, with the oil becoming hotter than the coolant after some hard driving, the temperature balance works the opposite way, the coolant serving to cool down the oil. The same principle is incidentally also used to cool the automatic transmission fluid on models fitted with Tiptronic, in which case the 911 comes with three water coolers at the front.

Good Cylinder Charge, Clean Emissions

Made largely of extra-light fibre-reinforced plastic, the intake system, thanks to its good flow dynamics, its carefully matched ducts and their smooth surface, makes a significant contribution to the superior output and powerful torque of the two boxer engines. The six intake manifolds leading to the intake valves join to form units of three on the other side leading into an air collector. A special feature to be found here on the engine of the 911 is the butterfly between these two resonance chambers opening at 2720 rpm and closing again at 5120 rpm. Thanks to this solution the cylinder charge, torque and engine power are all optimised in one and the same process.

On the other side of the engine emissions flow through a stainless-steel emission system with two metal-based catalytic converters for thorough and efficient emission management.

A computer serves to mastermind the flow of sparks within the engine, with no less than 300 sparks per second whenever the six-cylinder is running at 6000 revolutions per minute. Thanks to anti-knock control the computer is able to determine the right ignition timing even when running on low-grade fuel with a quality level worse than premium plus. And the injection system with electronic management operates as reliably as ever, delivering 300 or more exactly metered bursts of fuel per second to the intake valves at exactly the right time.

Innovative technology of this calibre gives the water-cooled boxer engine of the Porsche 911 superior output of 300 bhp (221 kW) at 6800 rpm. Maximum torque, in turn, is 350 Newton metres or 258 lb-ft at 4600 rpm. But even this kind of progress, as clearly as it is described by these figures alone, cannot match the experience of actually driving the car.

The water-cooled flat-six power unit in the Porsche 911 really reveals its true qualities when required to run at high engine speeds, where it combines supreme torque with almost unlimited free-revving performance up to 7000 rpm and more.

The sound accompanying this new fortissimo of speed and performance naturally remains within the limits prescribed by law, but just as naturally retains that typical Porsche quality. So this certainly is the Porsche six-cylinder boxer with that throaty chortle so typical of the marque.

Porsche Stability Management (PSM)

Extra Driving Safety All-Round

The new 911 Carrera 4 is the first-ever Porsche to feature Porsche Stability Management (PSM), a combination of four-wheel drive designed consistently for sports motoring and electronic suspension control carefully geared to the character of the car. The result is not only a high standard of driving safety, but also that very special driving pleasure Porsche drivers have learnt to appreciate so much over the last 50 years.

This objective calls for control and suspension management features different from those to be found in other cars incorporating similar systems. For PSM is conceived and designed for a routined, committed style of motoring. A Porsche will retain its agile, sporting and dynamic driving behaviour all the way to the most extreme limit. And thanks to the high standard of safety reserves offered by the suspension, the driver only has to intervene in the car's behaviour on dry roads when driving under near-racing conditions. At the same time PSM discreetly and almost unnoticeably corrects any minor deviations in directional stability attributable to load change or application of the brakes in a bend.

Stopping Distances Even Shorter Than Before

Porsche's engineers allow PSM to intervene more energetically at an even earlier point on wet or slippery roads and, in particular, on road surfaces with varying frictional coefficients. And it is here, too, that PSM makes stopping distances much shorter while keeping the car stable and firmly on course when applying the brakes.

In its operation PSM follows two fundamental control strategies: First, it offers the well-known concept of longitudinal control with ABS anti-lock brakes, anti-spin control and the Automatic Brake Differential keeping the car smoothly on course when accelerating and applying the brakes on a straight or in bends.

Second, PSM also offers lateral or transverse control keeping the car reliably on course even when subject to substantial lateral forces in a bend. The corrections required for this purpose are provided by the specific, carefully controlled application of the brakes. Any tendency to oversteer with the rear end of the car swerving round is counteracted by the exact, perfectly metered application of the brake on the outer front wheel in a bend. Understeering, in turn, is prevented by applying the brake on the rear inner wheel. Lengthwise dynamic control also comes in here to provide a supportive effect, E-Gas technology in the Carrera 4 serving to adjust the position of the throttle butterfly according to specific requirements. On the road, this means much easier and smoother steering.

To ensure precise function at all times, PSM features a whole number of monitoring units. The wheel speed sensors introduced for the first time together with ABS not only provide information on the speed of the car, acceleration and deceleration, but are also able, by considering the difference in speed from left to right, to "detect" bends and their radius. Further units are the steering angle sensor, a lateral acceleration sensor and a yaw sensor serving to detect any drift inclination of the car.

PSM: Faster Than Even a Routined Driver

All data determined by the sensors are stored within the PSM computer, evaluated within fractions of a second and passed on as instructions to the E-Gas or brake system. As a result, PSM responds a lot faster in threatening situations than even the most routined driver.

Really enthusiastic drivers wishing to try out the "natural" dynamic behaviour of their Carrera 4 on the race track are able to temporarily deactivate the lateral dynamic control provided by Porsche Stability Management simply by flipping a switch on the instrument panel. And even then the risk involved when taking the car into a power slide is reasonably limited, since all the driver has to do when the angle of the car becomes excessive is to step on the brakes in order to reactivate the dynamic control function. So under circumstances like this PSM is able to slightly "bend", but of course never fully override, the laws of physics.

The Market Position of the New Carrera 4

First Class Business Express

In recent years about 30 per cent of all purchasers of a Porsche 911 have opted for the four-wheel-drive version. And now Porsche's marketing and sales experts believe that the new Carrera 4 will exceed even this large share in total sales.

Over and above four-wheel drive, the new Carrera 4 differs more than its predecessor from the "basic" model, both Porsche Stability Management and sidebags fitted as standard providing a significant increase in value. And the cabriolet, of course, comes as standard with the hardtop as well as rollbars extending up automatically in a dangerous situation. So in all, the two versions of the Carrera 4 offer the customer a genuine price benefit compared with their predecessors.

New: Four-Wheel Drive with Tiptronic

The considerable improvement of driving safety ensured by four-wheel drive and PSM, particularly under difficult driving conditions, again makes the Carrera 4 appeal to an even larger group of prospects. And the combination of four-wheel drive with Tiptronic S now available for the first time makes the Carrera 4 an even more attractive car for the aficionado of automatic transmission motoring.

Boasting features of this kind, the Carrera 4 appeals to purchasers in the business car market even more than before.

In a nutshell, therefore, the four-wheel-drive model significantly upgrades the everyday driving qualities which have always set the Porsche 911 aside from other sports cars in this category, thus achieving an even higher, unprecedented level. And a further important point is that not only the Carrera 4 coupé, but also the cabriolet with its hardtop fitted as standard and its low noise level, is the perfect car for fast long-distance motoring in comfort and style.

From the Lohner-Porsche All the Way to the New Carrera 4

Almost 100 Years of Porsche Four-Wheel Drive

Professor Ferdinand Porsche first had the logical idea to drive all four wheels of a car back in the year 1900. At the time he was developing automobile concepts for Lohner, a motor carriage factory in Vienna, where he used electric hub motors to provide the necessary power. On the first prototypes only the front wheels were driven, but in September 1900 a Lohner-Porsche with hub motors on all four wheels went to E W Hart, a customer in Britain.

Ferdinand Porsche then chose the same solution again in 1912 for the Austrian army's Landwehr-Train, a petrol engine driving an alternator serving to feed electric power to the hub motors in the various trailers forming this off-road "load train".

In his position as Technical Director of Austro-Daimler, Porsche was of course also interested in mechanical four-wheel drive. Accordingly, he started developing trucks for Austro-Daimler as of 1906, where not only the rear wheels, but also the front wheels were driven by shafts and bevel gears.

The problem of finding the right drive joints for front-axle drive, which remained unsolved in the early years of the automobile, also forced Porsche to take a long break in following up his idea. Indeed, he was required to circumvent this difficulty also with his next four-wheel-drive vehicle, the Mercedes-Benz T80 speed record car completed in 1939 featuring three axles of which only the rear two, as on a truck, served to convey the power of the engine to the road.

Beetle Chassis with Four-Wheel Drive

As early as in 1934 the Porsche Design Office initiated fundamental studies to develop "genuine" four-wheel drive in the process of developing the Volkswagen. Indeed, it was in this year that Senior Engineer Karl Rabe designed a Beetle chassis with four-wheel drive, creating a concept later to become popular above all for military purposes.

Following World War II Ferry Porsche, the son of Professor Porsche, continued this tradition of four-wheel drive, building a Grand Prix racing car for Italian manufacturer Cisitalia with a 1.5-litre 12-cylinder in mid-engine arrangement. Boosted by a compressor to maximum output of approximately 420 bhp (309 kW), the power of this outstanding engine was transmitted to all four wheels. Unfortunately the car never saw the race track, since Cisitalia went bankrupt before the first race.

The next step taken by the Company was to build a four-wheel-drive vehicle for the Porsche brand itself. This was Porsche's version of the classic Kübelwagen built in Zuffenhausen in the early '50s when the German Bundeswehr asked car manufacturers for their tenders for a light off-roader. On this special design the driver was able to activate additional front-wheel drive, feeding the power of the air-cooled four-cylinder (1.6 litres; 60 bhp/44 kW) to the front axle. Porsche's Jagdwagen or hunting car was indeed built in small numbers and sold to private enthusiasts, while it was not able to hold its own as a military vehicle due to low-priced competitors.

Weissach was Ahead of Its Time

Porsche four-wheel drive then took a creative break until the '70s when the engineers at the Weissach Research and Development Centre started to take a closer look at front-wheel-drive vehicles with additional activation of rear-wheel drive offering a substantial improvement of traction through relatively simple and straightforward technology. The result of these studies was the prototype of a VW Passat Variant with four-wheel drive.

It was also at this time that the engineers in Weissach were finishing their first customer developments with four-wheel drive. And the first sign of the future featuring this technology made its appearance at the 1981 Frankfurt Motor Show in the guise of a 911 cabriolet incorporating four drive wheels. This four-wheel-drive concept based on the 911 was of interest above all to Porsche's Racing Division, where the specialists saw the opportunity to build a really superior competition car.

This first version of the Porsche 959 made its debut at the Frankfurt Motor Show in 1983, the new project proving its qualities convincingly only a few months later when a prototype of the 959 became the first-ever sports car in January 1984 to beat the tough off-road competition in the gruelling Paris-Dakar Rally. And in autumn of the same year the 959 brought home victory in the Pharaoh Rally in Egypt.

The Porsche 959 production car made its debut at the 1985 Frankfurt Motor Show, although it was now no longer what it was originally intended to be. With manufacturers making their racing cars increasingly sophisticated and complicated, the Group B rules and regulations applicable at the time were changed to the benefit of models closely related to their production counterparts. So Porsche's supercar had to switch over from the role of a racing car to that of a spearhead in technology. And it was indeed in this role that it impressively defined the state of the art. Boosted by two turbochargers operating in series, the six-cylinder boxer engine featuring air-cooled cylinders and water-cooled four-valve cylinder heads developed a massive 450 bhp (331 kW) maximum output plus 500 Newton metres (369 lb-ft) of torque from 2.85 litres. This kind of power was transmitted smoothly to the road by four-wheel drive using computers to monitor and control the distribution of engine power. A hydraulically operated multiple-plate clutch controlled the flow of power to the front axle and the differentials also featured fully controlled multiple-plate lock-up clutches.

In 1989 this concept of four-wheel drive made its logical move into larger production volumes in the new version of the Porsche 911 now code-numbered the 964, which featured 959 four-wheel-drive technology in somewhat simpler form. The flow of power to the front axle was controlled as before by a hydraulically operated multiple-disc clutch, the rear axle was equipped with a variable differential lock.

Optimum Traction and Agile Driving Behaviour

Ongoing development of four-wheel-drive concepts both for customers and internal, in-house projects allowed Porsche's engineers to develop simpler and even more effective solutions in the course of time. Accordingly, the next generation of the 911, the 993 introduced in 1993, featured a new system of four-wheel drive using a viscous clutch to distribute power between the two axles – without a computer or any kind of hydraulic technology. Similarly, there was no hydraulic support for the limited-slip differential on the rear axle.

This new solution quickly gained great popularity through its ideal combination of excellent traction and agile driving behaviour typical of the Porsche 911. And since 1995 it has even proven its qualities in the ultra-powerful Porsche Turbo entering the market with maximum output of 408 bhp (300 kW) and finally achieving peak power of 450 bhp (331 kW) plus maximum torque of 550 Newton metres (405 lb-ft).

Now the new Carrera 4 is the next logical step along these lines. Again, it incorporates a viscous clutch to adjust the flow of power to the front axle. But the big step into the future is taken by the car's electronic system incorporating Porsche Stability Management to control the car's driving behaviour especially when pushed to the limit.

Technical Data