Turbocharged engine lifts Porsche 911 to new heights, while four-wheel drive gets the power on the road. 996 model now, 997 coming...
With 420 bhp and a top speed of 190 mph, the 911 Turbo is a very quick supercar, and unlike many that screech up to that speed, the Turbo gives you stacks of power at any speed. It takes just 4.2 seconds to get to 60 mph, not quite able to get into that elite sub 4.0 seconds group.
Last of the 996s with distinctive appearance
Still, you'll need to be driving a lot of different and very fast cars to notice. The Turbos are immediately recognised by the large rectangular air intakes beneath the headlamps and the small air intakes in the sides of the car just forward of the rear wheels. There are also a couple of air outlets at the sides of the rear skirt.
Otherwise, you get the looks of the 996 version of the 911 - the latest Carrera is the 997, and the more potent 997 models are soon to appear.
'Otherwise' is an understatement because those air intakes and outlets give the car a more potent look. You also get very fat tires. Despite these changes the aerodynamics are still good - the Turbo has a drag coefficient of just 0.31, and not much high speed lift.
It's a bit wider that the standard 911, so drag will be a little higher, though. The car is widest at the rear where the wheelarches have been widened to increase width by 2.5 inches (60 mm).
Based on the 3.6 liter flat-six twin ohc engine of the 911, the Turbo has twin turbochargers and intercoolers to get cool charged air into the cylinders. Full boost of 1.80 bar is reached right down at at approximately 2700rpm, which is why so much torque is available over such a wide speed range. Boost pressure is reduced slightly as engine speed increases, and is around 1.65 bar at maximum power.
For 2004, the VarioCam Plus variable valve timing system was adopted. Instead of just varying the opening point of the valves while maintain the same total opening, the VarioCam Plus is based on the use of two different cams for each valve - like the VTEC system pioneered by Honda. This system gives better performance than the type where the cam is rotated to alter the opening point.
Dual tappets
Honda uses rockers to actuate its system, but in the Porsche system the valves operate a pair of concentric tappets sitting on the valve stems. The outer tappet is operated by the low-lift cam at low speeds, and the high-lift long-opening cam operates at high speed. The result is plenty of low-speed torque and massive power.
Thanks mainly to the VarioCam Plus, fuel consumption and emissions are reduced, but you still get masses of power.
420 bhp from 3.6 liters
Porsche quotes 420 bhp at 6,000 rpm, with 413 lb ft (560 Nm) at 2,700 to 4,600 rpm - what a stunning spread of torque that is! Not enough power? Get the 991 Turbo S, which develops 450 bhp at 5,700 rpm, with 457 lb ft (620 Nm) at 3,500 to 4,400 rpm. Surprisingly, the extra 30 bhp don't do much for the performance, just shaving 0.1-0.2 seconds off some acceleration times, but nothing you'd measure for 0-60 mph. Still, it really gives you that shove-in-the-back feeling anywhere from about 3,000 rpm upward.
Six-speed manual or Tiptronic
Both cars come with a six-speed manual gearbox, but you can have a five-speed Tiptronic to smooth out power delivery if you prefer. In either case of course, you'll have four-wheel drive to improve traction and help reduce the tendency to unstoppable oversteer - a lot of understeer is built into the suspension set up.
Suspension is similar to other 911s, with struts at the front and multi-links at the rear, with five separate links; coil springs and telescopic dampers, of course.
Stability control as standard
New for 2004 was the PSM (Porsche Stability Management) - that's Porsche's stability control which is intended to make sure that should you get to the limit, the control will bring you back to safety. Certainly, on a car with this amount of power and a rear-mounted engine it is not a bad idea.
Good torque split
The four-wheel drive system is designed to send 40% of the torque to the 225/40 ZR 18 tires, ands 60% to the much wider 295/30 ZR 18 tires. To vary the torque according to the amount of slip in any wheel, a viscous coupling is used as the center diff - this is the simplest and probably the best center diff.
With more than 60% of the weight on the back tires, you can see that the four-wheel drive system is biased toward stability.
The cross drilled brakes are larger than before, and there are four-pot callipers. You can have the optional composite ceramic discs, which reduce unsprung weight by about 50%, and which don't suffer from brake fade even in very tough conditions.
Both the 911 Turbo and Turbo S are amazingly powerful supercars -you need to control you right foot when you drive one. On the other hand, as with all 911s, they're very practical 2+2s, but tamed somewhat by four-wheel drive.
Want the power without four-wheel drive? Take a look at the even more powerful GT2....
