For a vehicle which was once regarded as a sign that Porsche had lost the plot, the Cayenne has been remarkably successful. Whether this is because Porsche owners want an SUV or SUV owners want a Porsche is irrelevant - the point is that the car has found a market, and contributed yet further to the company's status as the most profitable manufacturer in the world.
You could say that the Cayenne is not a "proper" Porsche, since it shares its platform with the Volkswagen Touareg and the Audi Q7. But, as we've found so often in the past, the same platform can be used to produce two or more quite different cars, and in this case there is no doubt which model has been developed by the company with the most robust sporting heritage.
Of the "new" Cayennes introduced for 2007, there is no doubt about which is the sportiest. The Turbo tested here benefits, like all the others, from a range of improvements, including a most welcome rethink of the previously rather alarming body design. Mechanically, its V8 petrol engine has been enlarged from 4.5 to 4.8 litres, with a corresponding increase in maximum power to 500bhp.
That's a chunky 50bhp up on what the old Turbo achieved, though it's still shy of the 521bhp provided by last year's Turbo S. But remember - say it after me, class - maximum power isn't everything. Despite the shortfall, the new car is pretty much as quick as the Turbo S was (well, slightly quicker, in fact, but by such a small margin that you'd hardly notice), and it's also marginally more economical than both that car and the previous Turbo. That's a good thing, as long as you're prepared to accept that combined fuel consumption of 19mpg is anything to be proud of.
If you find the idea of a 500bhp SUV alarming in a driving sense, there's nothing to be worried about. The Turbo is so docile in normal driving conditions that you might easily believe you had been given the wrong car. There is no fuss at all, largely because the accelerator pedal doesn't do much in the first few inches of its travel. You have to send it a lot closer to the carpet before the real action starts.
When you do this . . . oh, my. Those doubts that there is really a 500bhp engine under the bonnet vanish almost immediately. With a delicious roar (though not an intimidatingly loud one) the Cayenne heaves up like a racing powerboat getting into its high-speed position. Some cars feel like they are rushing towards the horizon, but this one feels like it has lassoed the horizon and is dragging it towards you.
Fortunately, the brakes have been uprated at the same time as the engine, so there's never much doubt that you can bring the Cayenne to a sharp halt if you need to. For those of you interested in the technicalities, the discs are larger than before (being now 368mm in diameter at the front and 358mm at the rear), the calipers are bigger too, there's more cooling than there used to be, and the system structure has been stiffened. One result of all this, Porsche claims, is that long-term brake performance has been improved by 10% compared with the old model.
The Turbo comes as standard with Porsche Active Suspension Management, which gives a choice of damper settings and ride heights (the latter allowing for greater clearance off-road, though the Turbo is probably the last Cayenne you would think of driving in those conditions).
There's also an Anti-Roll Stability feature which, through the use of automatically-adjusting rollbars, limits body lean in corners. A Porsche demonstration involving two cars going through a slalom confirmed that the new model does indeed lean far less than its predecessor, though there was also a noticeable increase in tyre squeal.
Pressing a Sports button switches the suspension to its firmest setting, and also makes the automatic transmission more willing to change down. Personally I found that the firm suspension was best for normal road use, at least as long as the tarmac is fairly smooth, but I could have done without the more frantic gearshifting - fortunately, it's possible to adjust them both separately.
The sporty suspension setting is also a Good Plan if you happen to take a Cayenne Turbo to a race track. You might wonder why anyone would think of doing this, and I was a bit surprised when Porsche offered me the opportunity of some quick lappery at Brands Hatch, but it turned out to be a very effective demonstration of what the Turbo can do.
With the exception of a Dodge Ram (long story), this is the tallest vehicle I have ever driven on a circuit, and it all felt very strange. It was like driving round a life-size map of Brands rather than the track itself, and Paddock Bend - a dizzyingly steep downhill right-hander even in a proper race car - was even more of a rollercoaster ride than usual.
On standard suspension, the Cayenne behaved like you would expect a well set-up but still hilariously inappropriate SUV to behave. In Sport mode, the difference was amazing. I thought the car suffered a little on the exit from Clearways on to the pit straight - a shade too much anti-roll thrown at the front axle when the system realised what was happening, and some consequent understeer to deal with - but apart from that the Cayenne handled with a poise that seemed ridiculous for something of this size.
A Porsche test driver told me later that his team had found the Turbo to be capable of lapping Brands quicker than a Cayman. That must be because of the Cayenne's enormous power advantage (it can reach 120mph past the pits before you have to brake for Paddock), and I'm sure the Cayman would have been a lot more fun in the corners. But still.
It's difficult to make a case for the Cayenne Turbo. This is hardly a car that anyone actually needs. But past experience shows that quite a number of people want it, and there's no doubt that the thing is extraordinarily capable, often in unexpected ways. I can't imagine owning one, but I can see the appeal nevertheless.
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