30 years of 4WD: Power to the four
Power to four or two wheels is a debate that’s gone on for 30 years now. That’s 30 years with the 911, anyway, since the 964 arrived in 1988 when ‘Carrera’ accompanied by a ‘4’ entered the lexicon of Porsche speak. Porsche is celebrating that 30 years of four-wheel drive using that 964 C4’s introduction as a useful line in the sand, snow or any other traction-limiting surface of choice to hang an anniversary off.
We all know that Porsche’s four-wheel drive didn’t start with the 964. Indeed, the Lohner-Porsche electric car of 1900 drove all four wheels via hub-mounted electric motors. Then, in 1947, Ferdinand Porsche built the Lohner-Porsche Type 360 Cisitalia Grand Prix racing car, its 12-cylinder supercharged engine able to drive all its wheels via an all-wheel drive system.
It would be motorsport again – specifically the Group B rulebook – which would see Porsche embrace four-wheel drive. The effectively open rules saw Porsche’s CEO Peter Schutz and head of research and development Professor Helmuth Bott throw every available technology and more at its revolutionary 959 hypercar. That it was four-wheel drive is no surprise, with Audi’s Quattro having already demonstrated the effectiveness of four-wheel drive on the world’s rally stages. Porsche’s new super 911 had to feature it.
Prototype testing underlined the effectiveness of driving all four wheels, Porsche developing the 953 for the 1984 Paris-Dakar rally. This heavily modified 911 ran a mechanically controlled 4×4 system and during three weeks and over 13,000km it dominated, René Metge and co-driver Dominique Lemoyne winning the famous race.
That 953 was the evolutionary step to the 959, which was first shown in concept ‘Group B Studie’ form at the 1983 Frankfurt Motor Show. The 959 would take the development of four-wheel drive to another level altogether. It remains a hugely complex and sophisticated system to this day, featuring what’s referred to as PSK (Porsche-Steuer Kupplung – roughly translated as Porsche control coupling) four-wheel drive system. It is unusual as it allows instant torque splits while driving, either automatically through its computer control or manually selected for various conditions.
Using an output shaft from the front of the gearbox, drive was pushed to the front axle via a prop shaft to a front differential via a multi-plate clutch. It is the 959’s multi-clutch arrangement that is unusual, it replacing a more common centre differential. Featuring six pairs of frictional plates, each controlled by hydraulic pressure and managed by the 959’s electronics, the system needed the wheels to run at differing speeds to work in normal conditions. Thus the 959’s front tyres have a rolling radius around one per cent larger than those at the rear. Should slip be detected at the rear wheels, or differing wheel speeds in corners, the clutches would engage accordingly, transmitting torque to the front axle.
For the full article, pick up your copy of Total 911 issue 164 in shops now or get it delivered to your door via here.