TIPTRONIC AND FOUR-WHEEL DRIVE
A semi-automatic system, the reputation of Porsche's Tiptronic transmission has been given a beating over the years, chiefly because, as you'd expect, the newer PDK (second-generation 997 onward) is a slicker unit with more instantaneous shifting. Both the 996's sequential Tiptronic and the later PDK, however, allow manual override — leave the gearbox in drive and let the car take care of shifting for regular driving, then switch to manual controls and move up and down the cogs as you see fit for spirited B-road blasting or track action. To achieve this, you use the steering wheel-mounted buttons to change gear. Some owners have found the flappy paddles introduced for use with PDK more intuitive. If this sounds like something you'd prefer, rest assured there are many online guides illustrating how to introduce paddles to a Tiptronic-kitted 996 or 997.
As we've just mentioned, you can use the steering wheel controls to change the automatically selected gear. Automatic gear selection will then resume. If you're adamant you don't want any assistance (track use, for example) you can put the gearbox into manual mode, thereby preventing the transmission from intervening.
Most people who knock Tiptronic have no prior experience of the system, which is hugely powerful and results in a quicker Porsche than the equivalent manual. Spend time learning how to use the system properly and you'll find it very rewarding. Reassuringly, unless the host Porsche is driven flat-out on the redline and down a steep gradient, it is virtually impossible to over-rev a flat-six mated to Tiptronic.
The primary four-wheel drive hardware underpinning C4S variants of the 996 and early 997 is identical to that used by Carrera 4 machines of the same generations. The entirely mechanical arrangement acts as an addition to the rear-drive system used by all 996 and 997 Carreras — two and four-wheel drive variants — and uses a Cardan shaft to bring power forward into a ZF assembly driving the front wheels. The construction contains two major components: an open differential and a viscous coupling. It’s the latter of these which gives the fourby versions of the 996 and 997 their ability to vary the percentage of power sent to the front axle.
An entirely automatic process, these changes are brought about by any speed difference between the front and rear driveshafts, which are connected to a dense collection of vanes within the viscous coupling, rotating inside a bath of heat-sensitive fluid. As driveshaft speed increases, the liquid begins to warm, becoming increasingly firm and sending energy forward from the faster-spinning rear vanes to the front. The Porsche system always transfers a minimum of five percent power to the front wheels, but this slowly rises with speed, reaching thirty percent at 155mph and spiking to forty percent when the rear tyres lose traction.
The coupling’s front axle location is a change from the centre-mounted all-wheel drive systems used in 964 and 993 Carrera 4s. This alteration allows the 996 and 997 system to dovetail with both a six-speed manual and five-speed Tiptronic gearbox. Current values vary little between the two transmission types, showcasing the adaptability of the Carrera 4 and Carrera 4S platforms.
The Tiptronic gearbox has demonstrated itself to be very reliable, but the cooling pipes have a tendency to rust after a few years of being exposed to dirt and road salt. Thankfully, replacing these parts is a relatively inexpensive job.