Chassis
Strangely, Porsche 959 was built on a steel monocoque essentially the same as the 911's. Since all its less expensive rivals like Lamborghini Countach and Ferrari Testarossa were using the inherently lighter tubular space frame chassis, one can inevitably doubt the effort Porsche had spent on weight reduction. Perhaps Porsche thought any new chassis advancer than steel monocoque could hardly be applied economically to its future production models, so why should it spend money in this subject ?
Instead of developing a radical
chassis, Porsche pursued lightness by using lightweight materials for body
panels -
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| Front lid and doors | Aluminium alloy | Lighter than steel and much cheaper than Kelvar |
| Nose section (bumper) | Polyurethane plastic | Lighter than steel and easy to repair |
| The rest of enclosure | Fiberglass-reinforced Kelvar | Hi-tech material. Strong yet light. |
Most magazines, books and websites over-emphasised the sophistication of 959's body materials. In fact, with just a little bit knowledge about other supercars, you will be amazed how little carbon-fiber composite used in the Porsche supercar. For instance, the Ferrari F40 applied Kelvar even in doors, bonnet and interior, although it had already got a tubular space frame chassis.
Porsche claimed steel accounted for just 49 % of the dry weight, compared with an average of 72% of European passenger cars in 1985. But when compare with supercars, its 1350 kg kerb weight could hardly impress us. A Lamborghini Countach with a big V12 weighed just 100 kg more, while Ferrari F40 undercut it for some 200 kg !!
Styling and aerodynamic
In fact, 959 was never purposely-styled. Because the chassis came from 911, all the important dimensions and hard points were fixed - the wheelbase was exactly the same as 911, the width exceeded 911 Turbo by 2.5 inches, mostly for accommodating wider tyres. The exterior shape of the cockpit section was nearly identical to its cousin, in which the doors, windows, windscreen and roof even had exactly the same dimensions. No wonder many car tuners could easily modify a 911 into a fake 959 !
Initially, it was quite difficult for me to accept its styling - perhaps we were too used to 911's classical shape so that anything looks half-911 and half-others would be perceived as strange. Honestly speaking, even if we ignored the "911 effect", it still failed to deliver the pure beauty and emotion like any Ferraris. In terms of design philosophy, 959 has none, because it was styled by functional requirements rahter than artistic sense.
One of the functional requirements was aerodynamics. The big front air dam, huge rear spoiler and wide skirts were created step by step in wind tunnel. They contributed to the superb drag coefficient of 0.31 - the best among all supercars (only to be equalled by McLaren F1 and Lamborghini Diablo). This was very crucial to its record-breaking top speed.
Engineers could have reduced the drag further, but they did not want to sacrifice the zero aerodynamic lift they had already acheived. For a supercar running in excess of 300 km/h, any aerodynamic lift could cause serious problems in stability. Obviously 959's air dam and the fiberglass-Kelvar flat undertray contributed a lot to that.
However, 959 did not create any downforce either, unlike Ferrari F40 and today's 911 GT1. This explain why it was later discovered as lack of track-racing potential.
Engine
The 2849 c.c. flat-six shared virtually nothing with the 911, because it was derived from the racing unit that powered the 956 and 962 Group C racers. Unlike the famous air-cooled engine using by the contemporary 911, it was water-cooled because the excessive heat generated was impossible to be cooled by air. The basic structure was anything predictable: aluminium alloy head and block, aluminium forged pistons finished with polishing, titanium con-rods, 2 camshafts in each bank driving 4 valves per cylinder, dry sump lubrication .... all operation managed by Bosch's latest version of Motronic management system.
As
in 956 / 962's engines, it got a pair of small KKK turbochargers. However,
they were arranged to operate sequentially for the benefit of responsiveness
- below 4,000 rpm, since exhaust gas was not enough for driving both turbines
efficiently, all the exhaust gas was fed to a single turbo. This made the
turbo operated earlier than conventional turbochargers. Between 4,000 and
4,200 rpm, the second turbo "pre-spin", that is, prepared for engaging
very soon. Above 4,200 rpm, two turbos operated simultaneously to provide
full boost up to 0.9 bar (12.8 psi). At this moment, or 6,500 rpm, the
engine developed the maximum power of 450 hp, which was the highest record
for a road car if you do not believe the figure quoted by Lamborghini Countach
QV (455 hp).
In contrast, torque seemed to be a little bit disappointed. At 5,500 rpm you got only 369 lbft, well below the 425 lbft of Ferrari F40. Luckily, at least the delivery of torque was quite linear. Since the first turbo started operating hard at 2,500 rpm, no less than 296 lbft was available. It gradually increased until the second phase of boost started at 4,200 rpm, then jumped to the maximum in 5,500 rpm. In short, it had a very good manner for a turbocharged engine of this level of performance.
In order to compensate the lack of torque, as well as to cope with the near-200 mph top speed, Porsche developed a 6-speed gearbox with Borg-Warner.
PSK 4-wheel drive
This is the highlight of 959's technology breakthrough.While other supercar makers insisted to remain rear-wheel drive (mainly for cost and weight concern), Porsche demonstrated the superiority of 4WD with the 959. Those who have ever driven the 959, Bugatti EB110, Ferrari F40, F50, Jaguar XJ220 and McLaren F1 agreed that the first 2 provided much better "real world performance", that is, running on wet or slippery surfaces, or rough twisty roads. Undoubtedly, this is the inherent advantage of 4-wheel drive.
Porsche 959's PSK (Porsche-Steuer Kupplung) system was like no others. Even in today, it is still regarded as the most sophisticated 4WD system ever made. What made it so unique and so superior? Among all 4WD designs, PSK is the only one which could vary the front / rear torque split ratio under normal running condition, while other designs can only vary when tire slip occurs.
In most of the time, torque split between front and rear was 40 : 60, that is, the same as the car's weight distribution. This made the best use of traction.
In hard acceleration, PSK transferred up to 80% torque to the rear wheels. Why? Because hard acceleration leads to rearward weight transfer, which reduces traction at front wheels and increases traction at rear wheels. By transferring more torque to the rear wheels, the traction can be optimally used.
On slippery road, 50 : 50 torque slit was used. In any time, computer determined the most suitable torque split ratio by analysing parameters such as throttle position, steering angle, g force and even turbo boost. Therefore PSK system provided near perfect traction that was not comparable by other 4WD systems.
Mechanism
The
PSK 4WD system used a multi-plate clutch instead of center differential
to carry out the torque split. The clutch had 6 pairs of frictional plate,
each pair was independently controlled by computer and actuated by hydraulic
pressure. This was simply equal to 6 independent clutches.
To make this system work, the front and rear driveshafts must run at different speed in normal condition. (so 959 adopted a pair of front tyres with 1% larger diameter than the rear's) Because of the speed difference between front and rear driveshafts, the 2 frictional plates of each independent clutch were rotating relative to each other. When applied hydraulic pressure to the first clutch, a small amount of torque will transfer to the front axle. But note that the two driveshafts cannot be fully locked up unless all the 6 clutches are locked simultaneously.
Now, you can see how it worked: locked up 2 clutches, 3 clutches... and the torque to front wheels would be increased, subsequently, torque split could be 50:50 if all the clutches are fully locked up. Of course, all these action was controlled by computer.
This is only for "normal" condition. Like many other 4WD systems, when tyre slip occurred, most of the torque could be sent to either axle.
What about energy loss and wear due to the slipping clutches? As the speed difference was very small, Porsche claimed energy loss was no greater than 0.4% of the power developed by the engine. As for wear, the clutch was dimensioned that it was negligible and caused no problem during the whole life span.
Advantages
- Variable torque split even in normal condition. Best use of traction.
- Since computer monitored and controlled everything, theoretically it could cope with any normal or abnormal conditions without limited by the design of mechanical parts. The result was fast response and adaptive.
Disadvantages
- Heavy: with the complex multiplate clutch, PSK was heavier than ordinary 4WD.
- Expensive: it was so expensive that no other cars employed this design. In 1989, Porsche's 911 Carrera 4 tried a simplified version of this system, but without the most important variable torque split function. The second generation of Carrera 4 even dropped this and in favour of a much more conventional design.
Suspensions
The basic suspensions were nothing other than predictable: double wishbones in the front as well as the back. What amazed us were the adjustable ride height as well as the adjustable damping.The adjustable ride height function was designed to achieve high speed stability without hurting low speed ride. The driver could select a ride height of 12 cm, 15 cm or 18 cm according to need. For example, if the car was travelling off-road, he might need the largest ride height to prevent the car from bottom out or damaging by rocks. If he was just travelling at ease, he might also expect a comfortable ride which was only achievable by the longest suspension travel. However, if he was going to have a 300 km/h excitement in Autobahn highway, he must want the lowest ride height which lowered the center of gravity and stiffened the suspensions (by the shorter suspension travel as well as the adjustable damping) thus enhanced cornering stability.
The 3 ride height settings could be selected manually in the dashboard, or it could be done automatically by the computer. According to Porsche, FOR SAFETY REASON, no matter in what setting the computer would lower the ride height to at most 15 cm when speed exceeded 50 mph and further lowered to 12 cm when exceeding 100 mph. Well, it seemed that Porsche was either regarding its customers as ordinary drivers or it wanted to add another gimmick for advertising purpose. "Computer-controlled self-leveling suspension", isn't it sounds great ?
The adjustable damping also had 3 settings. Of course they varied the damping rate thus result in different stiffness.
To implement the adjustable damping and adjustable ride height, each wheel employed 2 dampers. One of which had an electric motor to vary the damper's valve system so to implement adjustable damping. Another damper, whose fluid was supplied by hydraulic pump from the engine, took care of the ride height adjustment.
Brakes
Porsche will never increase power without upgrading brakes, especially 959 was the heaviest member of the 911 family and was also by far the fastest. The ventilated discs (in Sport version, also cross-drilled) had diameters of 322 mm and 308 mm front and rear respectively, accompanied with a four-piston aluminium caliper which was yet to be matched then. The four-channel ABS, with sensors on all four wheels, was also the first ABS applied to supercars.
Tyres
Strange, very strange .... a German sports car used Japanese tyres as standard. Originally, Dunlop promised to development high performance tyres specially for 959, but technical difficulties delayed that until the 959 was already launched. Bridgestone, on the other hand, was eager to take part in this project and created the standard rubber earlier than Dunlop.Strange, very strange .... the rear tyres were just 255 mm wide. Ferrari Testarossa was 280 mm, F40 was 335 mm, Lamborghini Countach was even 345 mm !!
One of the reasons was: the PSK 4-wheel drive could optimally use the traction from narrow tyres. Another reason was: well, Porsche was actually too conservative. Remember the Bugatti EB110 which was also 4-wheel drive and was praised even more in terms of grip? This car had a pair of 325 mm rear rubber.