Cartella Produzione Porsche

Model Year 1995 "911 (993) Carrera 4" UK (25/08/1994)

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The new Porsche 911 Carrera 4 - New design, new approach, new performance.



Four-Wheel Drive for Superior Driving Dynamics and Maximum Traction

October 1994 at the International Birmingham Motor Show, will see the launch of the new 911 Carrera 4. Limited numbers of the Coupe and Cabriolet version are destined for the UK, and upon it's introduction in October it is expected to further enhance the sales performance of Porsche in the UK - currently 34% up on this time last year. Also, as a direct result of Porsche's production design improvement strategy which has increased efficiency at the Stuttgart factory, the price differentiation between the 2WD and 4WD versions of the 911 are closer than ever.

Lighter, faster and more dynamic than it's predecessor, the new Carrera 4 is the quickest Porsche from A to B currently available.



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The new Carrera 4 is a result of an extensive development programme, run in parallel with the 911 Carrera, and with the technology packed Porsche 959 as a bench mark, only a meticulously "fine-tuned" high-technology solution was able to fulfil the requirements. The new 911 Carrera 4 drive system combines the agility and driving pleasure of the rearwheel- drive 911 Carrera with the superiority of four-wheel drive. This Porsche four-wheeldrive system is one of the lightest systems on the market, and this fact is made even more significant when you consider that the new system weighs only half that of it's predecessor, and moreover, the friction losses have been reduced by 50%. The Porsche four-wheel drive system uses a viscous clutch and a transaxle shaft to the front axle, combined with a mechanical differential lock for the rear axle incorporating the Porsche 'Active Brake Differential' (ABD).
The low weight of the complete four-wheel-drive system in the new Porsche 911 Carrera 4 is remarkable - it is one of the lightest systems on the market. This becomes especially plain when it is compared to its predecessor. Until now, the extra weight totalled 100 kilograms, but the new system is just an exemplary 50 kilograms. This weight saving is the result of intelligent lightweight design and has a positive effect both on fuel consumption and driving dynamics. This effect is intensified by the fact that the mechanical friction losses in the power train have also been reduced by 50 per cent compared with those of the old system.

The main parts of the new Porsche four-wheel-drive system are:
- Four-wheel drive via a shaft with a central tube (transaxle) and a viscous clutch between the front and rear axles.
- A dynamic driving differential system for the rear axle. - The Active Brake Differential (ABD).

When a rear wheel slips, the viscous clutch automatically distributes drive torque between the axles. It always supplies the ideal amount of drive torque to the front axle. At the same time, it compensates for the difference in rotation speeds between the front and rear wheels when cornering.

The asymmetrical rear - axle differential lock applies a 25% locking effect when under power from the engine, and 40% when on over - run. This means that during engine braking, the lock creates a yaw force with almost twice as much tendency to understeer as when under power, which in the case of a load - change (ie abrupt closing of the throttle) in mid - bend has a stabilizing effect which keeps the car more precisely on course. Under acceleration however, the new Porsche 911 Carrera 4 exhibits the same agile, corner - hugging handling which has always been one of the most exciting features of the 911 - This new 4WD system further enhances the 911's legendary ability.

The Active Brake Differential (ABD) uses the data from the ABS sensors to determine loss of traction at individual wheels. The control unit then ensures that momentary braking force is applied to the wheel concerned, thus transferring drive to the wheel with grip, so as to restore optimum power transmission to the road. This function is active up to 70km / h. The complete system comprising four - wheel drive, viscous clutch, asymmetrical rear - axle differential lock and ABD, automatically provides maximum traction in any road conditions.

The new Porsche 911 Carrera 4 has retained the character of the rear - wheel - drive 911 Carrera, at the same time the smooth delivery and distribution of torque, without the driver having to intervene, makes for greater performance and directional stability in all circumstances. Above and beyond this, the 911 Carrera 4 automatically offers maximum traction on wet and icy roads. The combination of drive components and it's lightweight and efficient design, reflect the latest in engineering and sets new technological standards.

The new 911 Carrera 4 returns performance and fuel consumption figures that are practically identical to those of the rear - wheel - drive version. The fuel consumption of both models in accordance with the 'Euromix' formula amounts to 24.7 mpg (11.4 liters per 100 km). The Porsche four - wheel - drive system was equally gratifying in a comparison of performance figures too. The new Carrera 4 is quicker than the 2WD 911 Carrera: Top speed of 168 mph in both cases, acceleration 0-60 mph in 5.4 seconds (911 Carrera) and 5.3 seconds (911 Carrera 4). In dimensions, equipment and engineering the 911 Carrera 4 is the same as the rear - wheel - drive version, except for the drive system. Even the luggage compartment dimensions at the front remained unaltered due to the compact design of the front axle differential.

Despite the advances in technology, ability and performance, the price differentiation between the 2WD and 4WD versions of the 911 are closer than ever, with the new Carrera 4 priced from £ 58,245 for the Coupe and £ 63,245 for the Cabriolet version.

The features which distinguish the 911 Carrera 4 from the rear - wheel - drive 911 Carrera in engineering and appearance are as follows:

Engineering:
- Hydraulic brake booster and ABS
- 5 matched to 4WD system Viscous clutch and transaxle shaft to front axle
- Dynamic driving differential lock from the rear axle (25% / 40%)
- Active Brake Differential (ABD).

Appearance:
- Titanium - colored "Carrera 4" logo
- Tail - lamp units all in red
- Front direction indicator units in white
- Titanium - colored brake callipers
- Hub - caps with "Carrera 4" logo
- Titanium - colored gear lever inlay

The new Porsche Carrera 4 four-wheel-drive system in detail



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The viscous clutch is located at the transmission output, in front of the rear axl e, and is responsible for automatically distributing drive torque between the axles, as a result of wheel slip. It is connected to the compact, weight-optimized front axle differential via a hollow shaft. Because of the interplay between the multiple disc sets and the silicone oil charge, the maintenance-free viscous clutch operates in accordance with power output, rotation speed and temperature. At the same time the viscous clutch compensates for the difference in rotation speeds between the front and rear wheels when cornering. If the rear wheels show a tendency to spin, the viscous clutch reacts in fractions of a second by increasing the drive torque at the front axle. Because its performance parameters are matched to a specific vehicle, the viscous clutch always apportions the ideal amount of drive torque to the front axle and ensure driving stability under all conditions.

The dynamic driving differential system is designed to work asymmetrically. This means that under tractive force (drive force from the engine) the locking effect between the rear wheels is 25%, while on the overrun (deceleration) a 40% lock is applied. In engine braking mode, therefore, the lock creates a yaw force with almost twice as much tendency to understeer as in engine power mode. In the case of a load change (abrupt closing of the throttle) in bends, this then has a stabilizing effect which keeps the car more precisely on the desired curvature track. Under acceleration, however, and this was the development aim, and result, of a meticulous system matching, the new Porsche 911 Carrera 4 exhibits that agile, corner - hugging handling which is one of the most exciting features of the 911 and which has always been valued so highly.

The Active Brake Differential or ABD, which is standard (optional on the rear - wheel - drive 911 Carrera) ideally complements the action and effect of the viscous - clutch four - wheel drive system and the rear - axle differential lock. ABD uses the data from the ABS sensors to determine the drive slip at the individual wheels: the control unit then ensures that the appropriate braking force is applied to the wheel concerned, so as to restore transfer of power to the road.

If a difference in the friction coefficients between the left and right wheels occurs, the rear axle differential lock intervenes first, transmitting the drive torque smoothly to the wheel with the better grip. If this is not sufficient, and the amount of slip at one of the rear wheels is still to high, then the ABD control applies braking torque on the wheel opposite. This function is actuated at speeds up to 70 km / h and is of particular help when the weather conditions make starting off a problem. All in all therefore, the complete system comprising four - wheel drive, viscous clutch, rear - axle differential lock and ABD automatically provides maximum traction no matter what the state of the road.

The new Porsche 911 Carrera 4 has a four - wheel - drive system which is in keeping with the high standards of this powerful sports car and has thus been designed and tuned for optimum driving dynamics. The character of the rear - wheel - drive 911 Carrera has been deliberately retained unchanged. The smooth, slip - dependent distribution of torque, without the driving having to intervene, makes for greater directional stability in all circumstances. Moreover, the 911 Carrera 4 offers maximum traction on wet and icy roads.

The way the drive elements have been ideally combined, including the system's extensive use of lightweight design and its high efficiency, reflect the latest in engineering and set new standards. Above all, however, the result is a vehicle which returns performance and fuel consumption figures that are practically identical to those of the two - wheel - drive version a truly remarkable achievement, as a comparison of other four - wheel - drive cars with their corresponding two - wheel - drive models reveals.

The Porsche four - wheel - drive system was equally gratifying in a comparison of performance figures:

  911 Carrera 911 Carrera 4
Max. Speed 168 mph 168 mph
Accel. 0 - 60mph 5.4 sec 5.3 sec
0-1000 m 25.1 sec 25.3 sec

The curb weight of the 911 Carrera 4, at 1420 kilograms, is only 50 kilograms higher than that of the rear - wheel - drive version, which means that it is still 30 kilograms lighter than the former Carrera 4.

In terms of dimensions, equipment and engineering the 911 Carrera 4 is the same as the rear - wheel - drive version, except for the drive concept. Even the luggage compartment dimensions at the front remained unaltered due to the compact design of the front axle differential. The powerful six - cylinder horizontally opposed engine in the rear delivers a pleasing 272 BHP from a swept volume of 3.6 liters. Power is transferred via a six - speed gearbox. The safety - enhancing, yet comfortable chassis, with the sophisticated LSA multi link rear axle, was adopted from the Carrera. The brake system with a hydraulic booster and the ABS system were specially adapted to the four - wheel - drive system.

Even with four - wheel drive, the new Porsche 911 Carrera 4 exhibits exactly the same agile handling as the 2WD Carrera. In addition, however, it also offers superb driving dynamics, with exceptional traction dividends on wet and slippery roads. The automatically regulated, variable drive torque distribution ensures easily controlled handling. And the 4WD driver does not have to put up with less comfort in city traffic, either. Manouverability remains the same as in the two - wheel - drive version, as the drive system does not affect the steering.

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