A couple of years ago, the big V8 SUV was touted as the answer to active businessmen's ultimate driving needs. How quickly things changed.

Assembled here are three cars that have been selected to represent their genre rather than their brand. There will be one winner and one loser in the end, but this time it will not be the maker that wins or loses, but the technology that drives the car. And the result is a bit of a shock, if you would excuse the pun.

What this Cars in Action Green test is all about is to compare the three different powertrains currently available to the buyer of a premium sport utility vehicle. This is currently the only category of car where we currently find a compatible example of each and thus the choice of a trio of SUVs rather than say, three saloons or coupes?

The Audi represents the petrol engine ? at R675 000 the Q7 4.2 FSI V8 represents the cutting edge of petrol propulsion, its 257kW 440Nm 4.2-litre direct petrol injection V8 representing the acme of petrol engine deign.

Next up and twenty-odd grand less expensive is the BMW X5 3.0sd ? the all-new twin-turbo showcase of diesel technology. For just a 3.0-litre this one's quite impressive ? its 210kW and 580Nm multi-Engine of the Year credentials see it competing with V8 petrol and turbodiesel rivals 50 percent bigger in capacity and not only dealing with them in pure performance, but knocking them for a literal six when it comes to those ever increasingly important aspects of fuel consumption and emissions.

And then we get the joker in the pack: the brand new Lexus RX400h, the petrol-electric hybrid comprising a 3.3-litre V6 petrol engine aided and abetted by a pair of electric motors and a devilishly wicked system that charges its batteries by kinetic energy regeneration so that they're ready to help propel the car ? using no petrol at all in certain circumstances.

Surprisingly, the Lexus is the cheapest of this lot too. But, quite ominously, it's the least powerful despite relying on a literal gang of power plants' collective 200kW and 280Nm. Its fuel consumption however, is claimed to be better than both its rivals here.

The best way to look at this is to first consider the cars each in their own right, so let's start with that Audi.

Petrol - the classic SUV solution

Audi's first foray into the world of the sports utility vehicle arrived quite late considering the company's affinity with all-wheel drive through what it likes to call quattro. Looking at the car first before we get into the technical aspects, the Q7?s imposing nature is by design.

Audi reckons that its owners in this neck of the woods prefer a big, brutal car over something dainty like a TT, for instance, and thus this thing appears to be a bit more of a Merc GL rival then the ML rival it perhaps is.

Its styling divides opinion ? personally I like it but we have debated this one long and hard in the office and, to be quite honest, I doubt it's an argument that will ever be quite resolved. Yes Q7 is bold, big and imposing ? and it's selling by the dozen so it must be popular?

It's sumptuously equipped the Q7 but be warned, you will pay handsomely for a fully loaded one. Not everything you see on the test car is necessarily standard and that options list quickly hikes the price.

Under the skin, although the Audi shares its underpinnings with the Porsche Cayenne and Volkswagen Touareg, Ingolstadt sees Q7 as more of a road car than a Jeep and it lacks the transfer box and mud plugging 4x4 devices of its platform-sharing siblings, while its chassis is also tuned more toward road use than challenging the Caprivi.

But remember that the only reason the Audi is here is to represent the spark ignited internal combustion engine and our arguments henceforth will be based solely on that aspect of this car. Remember the Q7 also comes in the choice of two turbodiesels and a V6 petrol engine and there will also be a hybrid version of this car in the not too distant future. So do us a favour from hereon in and consider this as the petrol car rather than the Audi, OK?

So, let's look at that V8 then. Basically a detuned version of the brilliant 8000rpm unit found in the RS4 that revs a little less, this one's also shared with the A6 4.2 FSI we enjoyed a memorable long term test with a year or so ago. The normally-aspirated 4163cc unit is not very different from Audi's multi Le Mans winning FSI V8 either ? it has double-overhead camshafts per bank and four valves per cylinder while its party trick is its Audi FSI direct petrol injection.

This 84.5 x 92.8mm bore and stroke unit has a lofty 12.5:1 compression ratio, produces its 257kW at 6800rpm and a healthy 440Nm torque at a low enough 3500rpm. Audi claims the Q7 4.2 FSI will rush to 100km/h in 7.4 seconds and on to a governed 250km/h top whack and our Gauteng altitude tests caught it getting to 100km/h in 8.6 seconds to verify that claim.

Our tests additionally confirmed that the big Audi accelerates from 80 to 120km/h in 11.2 seconds and from 120 to 160km/h in 8.2 seconds. The Q7 runs a 16.6 second quarter mile at 143km/h. Audi's claims again reckon the Q7 can manage an average fuel consumption of 13.6l/100km and therefore produces 326 grams of carbon dioxide per kilometre.

Compared to other V8s of similar ilk, the Q7 offers similar performance to the albeit larger capacity BMW X5 4.8i and Merc ML500.

On the road, the Q7 is lively and interesting to drive and although it may not be quite as sharp as the driver-centric X5 here, it matches the Lexus well on the road and certainly does the job it's designed to do very well,

Diesel ? cleaner, leaner, faster

The second-generation X5 has refined what BMW calls its sport activity vehicle to a point of perfection. BMW likes to consider its cars as utterly driveable and this car is no exception. Dynamically ? in terms of driver feedback, involvement and enjoyment ? there still is only one SUV, sorry SAV, worth considering.

X5 makes a mockery of its bulk on the road and while it's by no means M5 wieldy, it's streets ahead among its peers. And for once this is a BMW that one can actually look at without cringing, its looks complemented by a finely balanced and high quality cabin and trim.

Like the Audi, though, you need to pile on the options to be happy, so while the vehicle in the pictures may offer basic spec, to have your cake and eat it adds a good 15-20 percent to the bottom line.

But under the skin this X5 is a masterpiece. While it lacks some of the very latest drive line trickery of the new X6 with its Xdrive and clever differential, it still has a fine chassis. But it's this car's brilliant diesel powerplant that really has us tickled.

Producing 210kW at 4400rpm and able to turn at a stunning-for-a-diesel 5000rpm, this 3.0-litre produces 580Nm at a most handy 2000rpm. The cherry on top here is sequential twin-turbocharging with a smaller snail taking care of the lower rev ranges before seamlessly switching over to a bigger, higher pressure turbine to look after the volume-hungry upper rev range.

We reckon this is the finest bit of turbodiesel tech out there right now and because it's still only available in X5, we chose it as the diesel representative for our experiment, rather than as a BMW.

The X5 also comes in the choice of a regular single-turbo diesel, a petrol six and a V8 and there is a hybrid and a powerhouse X5M in the pipeline, too.

Looked at in greater detail, this twin turbocharged and intercooled 3.0-litre inline-six oil burner is a state of the art twin-cam 24-valve unit with an alloy head and iron block. It has a bore and stroke of 84x90mm and a 16.5:1 compression ratio to help it achieve dizzying specific power and torque ratios to exceed even those of the BMW M5's petrol V10.

The Variable Twin Turbo mill furthermore employs variable vane geometry in both turbochargers and benefits second-generation Common Rail technology, specially adapted injector nozzles and specifically reinforced crankcase construction with particular attention paid to the crank bearing area to cater for its exceptional outputs.

BMW reckons sd can shift its two tons to 100km/h in just seven seconds and our Jo'burg test saw it achieve that in 8.6 seconds to match the V8 petrol car here. But that turbodiesel shove saw to it that the Beemer managed a substantially quicker 6.1 second pull from 80 to 120km/h and took 8.9 seconds to get from 120 to 160km/h. The top-drawer turbodiesel also shaded its high-tech petrol V8 rival to the quarter mile by a couple of tenths of a second albeit that the V8 was 1km/h faster at that point.

But the big difference - and especially in this Green Edition Shootout - the BMW uses more than a third less fuel - and produces a third less emissions - to do the same job that the more expensive petrol V8 does?

As noted above, X5 is a pretty sharp driving tool and this is one of very few cars these days that still has a waiting list on it. And its premier turbodiesel driving experience is quite a hoot, let alone a most gratifying experience?

Hybrid - the best of both words

Lexus? RX is a little long in the tooth. You wouldn?t say so looking at it alongside its two newfangled rivals here, but check a little closer and climb inside and that fact quickly becomes quite apparent. RX is to be replaced as a platform next year, so those little last generation Japanesey traits should be banished to the history books by then if the more recent GS is anything to go by.

The Lexus also comes fully loaded and there?s no need to be overly concerned by how much some or other options list is going to affect your deal.

Under the skin though, RX400h is a bit of a revolution. We go into greater detail on how the new Lexus Performance Hybrid system works elsewhere this issue so we won?t get too into all that again here bar to mention that in this application, the hybrid system has a 123kW 333Nm electric motor on the front axle and another 50kW 123Nm motor on the rear axle to fit in with its all wheel drive system. Naturally the system includes the 155kW 288Nm 3.3-litre quad-cam 24-valve petrol V6 mill that drives a continuously variable transmission on its own or in tandem with one or both of those electric motors.