In the pursuit of the ultimate workhorse, Nissan is treading where others have failed.

Its high-output turbo diesel Navara 550 ST-X is the fastest production one tonner in its class.

Explore the 2012 Nissan Navara Range

The hi-tech 3.0-litre V6 engine pumps out 170kW and 550Nm of torque, or 30kW and 100Nm more than the 2.5-litre four-cylinder turbo diesel version.

But it is also 150kg heavier at a paunchy 2117kg. Offsetting this is the V6's seven-speed automatic transmission, two more ratios than the 2.5.

It has a low first gear ratio to get it off the line, multiple middle ratios to keep it on the boil and a tall top gear. After a brief pause as the turbo spools up, step off is sharp, it pulls strongly in the middle range and lopes along on the open road with the engine ticking over at 1650rpm at 100km/h.

Nissan claims the 550 will sprint to 100km/h in 7.5 seconds, which puts it clearly at the top of the segment. But in general use it doesn't feel that much quicker than the 2.5.

The transmission is smooth and decisive enough but the calibrations have it holding on to gears longer than expected given the peak torque comes in at a low 1750rpm. This is presumably to help the transmission keep its cool when towing.

It can be coaxed into shifting up earlier by using the sequential shift, but that tends to defeat the purpose of an automatic. On the flip side it is eager to shift down on trailing throttle.

The engine is relatively quiet on idle but there is no doubt it's a diesel when moving. Fuel use on the combined cycle is 9.5l/100km compared with 9.0l/100km in the 2.5.

Price and equipment

The 550 ST-X costs $60,990 or $64,990 with a premium option pack. Apart from the engine and transmission, the additional features over the $50,990 2.5 ST-X include a hard tonneau cover linked to the central locking system, a black sports bar, fog lights, headlight washer, privacy glass, a tub liner and light, rear underseat storage, an engine immobiliser and 550 badges, mats and key ring.

The premium pack adds satellite navigation, leather seats, a reversing camera, a DVD player, Bose audio and powered and heated front seats.

Does it make sense to shell out the extra $10,000 over the 2.5 ST-X? Yes if you want the ultimate Navara. But if you want refinement as well as performance, then the 550 will leave you wanting.

So, can the 550 succeed where others have fallen? Toyota tried it with the TRD HiLux and it failed to generate enough interest to guarantee its survival, but then that was a petrol engine. The benefits of a diesel may just be enough for Nissan -- time will tell.

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