As good as the 3.0TDI diesel engine is, Audi's Q7 rather swamps it. What was needed was something bigger and brawnier to power this leviathan SUV and it's here in the shape of the 322bhp 4.2 V8 TDI. An economy figure of 25.4mpg and an ability to get from 0-60mph in 6.2 seconds speak volumes.

Start reviewing any vehicle the size of the Audi Q7 and the familiar theme of urban 4x4s soon raises its head. For once, let's put that argument to one side and just celebrate what is, by any standard, an incredible piece of engineering. The Audi Q7 4.2TDI features a diesel engine that can not only beat the fuel economy figures of many petrol-engined family saloons but also has the pace to keep a proper sports car honest. Prices start at around £50,000.

Revealed for the first time at the 2007 Geneva Auto Salon, this car's engine is the successor to the Volkswagen Group's incredible 5.0-litre V10 TDI unit - a powerplant that wouldn't comply with ever stricter emissions regulations. So it is that we get this smaller, cleaner but more powerful turbodiesel fitted to the flagship Audi 4x4. That might be what many would call working smarter, not harder.

The Q7 chassis will never be at the sportier end of the luxury 4x4 continuum but it's nevertheless a tidy handler. The car could use a little more steering feel but the standard fit adaptive air suspension allows the Q7 to be dropped into a 'Dynamic' low ride height mode when you want to hustle and hustle you will with this powerplant. Cranking out some 760Nm of torque, this engine is more muscular than many fully-fledged supercar units. Lamborghini Murcielago LP640, Ferrari 599GTB, Porsche Carrera GT, McLaren F1 - none of these can match the torque of the Audi.

The best part about this engine is that the vast reserves of torque allow it to run at low engine speeds while still generating all that muscle. In fact, you need barely exceed tickover as peak torque is available anywhere between 1,800 and 2,500rpm. Should you wish to extend it, the Q7 4.2TDI will bludgeon its way to a top speed of 146mph. The Q7 makes a superb motorway cruiser with its suspension set into cosseting 'Comfort' mode although the six-speed tiptronic gearbox is best locked into sixth gear on long journeys as it does seem rather keen to kick down a gear or two rather unnecessarily.

"This diesel is an incredible piece of engineering "

As good as the Q7 is on longer runs, get it in town or in tighter country lanes and you'll soon appreciate that it's a sizeable thing. You'll probably look at two or three parking spaces before finding one that the big Audi will fit into and that gets tiresome quickly. It runs on a stretched version of the Volkswagen Touareg chassis and features a seven seat configuration, making it ideal for bigger families. If you can get away from the rugged mud plugging mentality and instead think of it as a multi-purpose estate car on growth hormone, you'll bond with the Q7 a whole lot quicker. Even its styling seems to distance it from off-roaders.

The coupe-like dipping roofline isn't standard 4x4 fare, nor are the resolutely horizontal shoulders. Audi even offer contrasting body colours in a bid to emphasise the car's shapely profile. Audi claim 28 seating and loading configurations are available in the Q7 and the seats in the second row are adjustable for fore/aft movement. This allows Audi to not only lay claim to the most generous second row legroom in the class but also - with the second row slid forward and the rear folded - to also pinch first prize for luggage capacity, a huge 775 litres.

The Q7 4.2TDI comes stacked with equipment. Full leather trim is a standard fit, as are inlays in three different types of wood or aluminium. The front seats get electric heating as standard, a notable omission even on S-line variants of other Q7s. There's also an onboard coimputer, cruise control and multifunction steering wheel. Somewhat surprisingly, there's still nowhere to plug your iPod in. Adaptive cruise control and lane departure warning systems are optional. You can even specify 21-inch alloy wheels if you really want to destroy ride quality.

There are, nevertheless, some extremely thoughtful touches to the Q7. The ability to raise the tailgate from the keyfob is one that draws jealous glances from other 4x4 owners. Likewise, the ability to raise the car on its air suspension going from autoroute bullet to almost monster truck clearance in a matter of seconds is also something it's tough to get tired of. What really impresses about the Q7 though is just how accessible all of these systems are. Yes, there are manuals in the glove box that together total over 700 pages but you'll rarely need to consult them. Unlike in a rival BMW or Mercedes, there are very few times when the control systems flummox you.

Despite the fact that the Q7 4.2 TDI can manage a combined fuel economy figure of 25.4mpg, don't think for a minute that this will be an inexpensive car to run. Driving it in stop/start traffic will see that figure dip into the mid teens and it has the sort of parts prices you'd expect of a top end manufacturer. Ding one of those alloy wheels and you'll need deep pockets to replace one. Likewise, insurance is not a trifling matter and even a car as impressive as this is not immune to quite hefty depreciation, especially as the tide of public opinion may well swing against such vehicles.

If you need a spacious seven seat vehicle and can afford the Audi Q7 4.2TDI, there's very little reason why you shouldn't indulge yourself. What are the alternatives? You could opt for something like a top of the line Chrysler Grand Voyager or Renault Grand Espace but neither of these have the image of the Audi nor do they possess an engine as efficient. This leaves other 4x4s such as the new BMW X5 or the Volvo XC70. If you're a keen driver, the BMW might well edge the decision but there's something about the Q7 that's enormously appealing. Perhaps it's the accessibility of its functions or the fact that it's just so easy to drive. Only in confined areas do you feel its bulk. It's impossible to escape the sense of wonderment this engine generates though. It defines this vehicle and puts rivals in the shade. It's almost worth the price of admission alone.

TOP 2 Q7 DEALS

The results below show the top Q7 deals on buyacar

	Audi Q7 4.2 TDI Quattro S Line 5dr Tip Auto Estate
	ETR	Mthly £806	Saving £3,648	Price £47,042
	Audi Q7 4.2 TDI Quattro SE 5dr Tip Auto Estate
	ETR	Mthly £811	Saving £3,648	Price £47,042

typical 9.44% APR

PCP finance quote over 48 months,  10,000 miles pa,  deposit of £1000