The 2.2-litre HDi twin-turbo powerplant might be a touch down on power compared to the Citroen C6's six-cylinder engine options but because it keeps costs low and retains the model's core strengths of refinement and long distance comfort, it looks a sound choice.

There was a time when you'd have been laughed out of the golf club member's lounge if you owned up to anything less than a throbbing V6 under the bonnet of your executive wheels. Today, thanks to the nation's burgeoning environmental conscience and the best efforts of the taxman, things have changed. Citroen's C6 is nothing if not unconventional and without the macho pretensions its Germanic rivals are compelled to live up to, it should be well capable of carrying off a four-cylinder diesel. Especially a four pot like the 2.2-litre twin turbo HDi.

Car manufacturers tend to go one of two ways when deciding on the engines that a new model should be offered with from launch. Many will kick things off with the more middle-of-the-road, less exciting powerplants and add the headline-grabbing units over time to prolong interest. Alternatively, some will go all out with the big guns from the word go hoping to make the initial splash as large as possible. There are obviously issues surrounding the availability of different powerplants that are brought to bear on such decisions but in the case of Citroen's C6 - a premium executive saloon campaigning without a premium badge - the decision to hit the market with an all V6 engine range helped to push it up in the estimations of buyers. Once the car was into its stride, it was safe to bring in the 2.2-litre four cylinder petrol unit that arguably makes the big Citroen a more attractive proposition.

Having been touted as something of a thinking person's choice in the executive sector, the C6 looks a good match for the 2.2-litre HDi engine on paper. In no way is Citroen's flagship model the one to choose if you're in the mood to give your favourite section of B-road a good mauling. Instead, it's a car in which to take it easy and enjoy the impeccable ride quality served up by the Hydractive self-levelling suspension. The 2.2-litre engine uses twin turbochargers to help it gel with the reserved road manners of the C6. The parallel sequential dual turbo system, to give it its proper name, works to produce a smooth and progressive supply of torque from low in the engine range, eliminating the lag and lunge often associated with less sophisticated diesel installations.

"The C6 looks a good match for the 2.2-litre HDi engine on paper?."

Straight line speed is adequate, with the 2.2-litre HDi C6 taking 9.5s to complete the 0-62mph sprint and eventually easing its way up to a 135mph top whack. There's 173bhp to play with and maximum torque of 370Nm is produced at an ultra low 1,500rpm. It's a good deal less than the 208bhp and 441Nm of the 2.7 HDi engine that's also offered with the C6 but in a shoot-out with the BMW 520d (163bhp and 340Nm) or Audi's A6 2.0 TDI (138bhp and 320Nm), the C6 looks strong. Problems only arise for the Citroen when you realise the BMW is around £1,000 less and the Audi undercuts it by £2,500.

The C6 is a commendable piece of work on the part of Citroen's design team. The shape is resolutely modern but at the same time the proportioning, rather than the detailing, is reminiscent of classic Citroen shapes from the past. The elegant arc of the roofline and the long front overhang are redolent of the old DS and SM models, while the short rear overhang and low slung back end reprise some classic Citroen themes. The company claims that the target was to develop a car with the stance and presence of a limousine but with the chic silhouette of a coupe. They may just have succeeded.

A long wheelbase and low slung posture are quite unlike anything else on the road at the moment. Even one of Renault's wilder flights of fancy looks a little tame compared to the C6. The windowline across the curve of the roof arch is picked out with a subtle chrome strip - a clever asthetic trick that helps visually elongate the car. The frameless glass of the doors also helps here, removing the need for bulky door pillars that would otherwise break up the impact of the remarkable glasshouse.

The interior feels like that of a premium brand product, if not one of the real top dogs in terms of fit and finish. Without doubt, it gives us a different perspective on what Citroen can achieve in this regard. Space in the rear is extremely generous and there's a very nice detailing to keep passenger in the manner in which they are accustomed but the boot isn't quite as capacious when compared to other models in the class.

The 2.2-litre engine is offered with all three of the C6 trim levels so buyers get to select from standard, Lignage and Exclusive. Prices start at £28,395 for the standard model topping out at £34,695 for the Exclusive. The engine is only available with a manual gearbox which isn't quite in-keeping with the languid style of the C6.

Packed with technology, the C6 features a head-up display that projects speed and navigation instructions onto the windscreen. There's also a comprehensive driver's information system, electronic parking brake, the innovative lane departure warning system, directional Xenon headlamps and a speed limiter. Refreshingly, most of the headline-grabbing features appear even on the entry-level models.

The D word is a constant thorn in the side of any manufacturer that ventures in to the executive saloon sector without a respected premium badge to slap on the nose of its entry. As a result, the C6 depreciates like a snowmobile in the Sahara. It's an unfortunate fact of life that helps to make Citroen's flagship a stupendous used buy and the 2.2-litre engine about as sensible as the engine options get if you are going to buy new. By opting for the cheapest model, you're exposing as little of your cash as possible to the car's plunging residuals. You also get to save more cash on fuel with the 43mpg average economy (the larger 2.7 V6 HDi manages a rather disappointing 32mpg) and tax with the 175g/km CO2 emissions.

Performance isn't the point of the C6 so why not get the most affordable and economical engine so you can enjoy the car's best bits with the minimum impact on your own bottom line? The 2.2-litre HDi twin turbo unit does sterling work maintaining levels of refinement in the cabin and it rarely feels like it's lacking the power to keep the substantial C6 moving.

The V6 petrol and diesel engine options might appeal on the basis that you can't have a proper executive saloon without a six-cylinder engine but putting such outdated notions to one side, it makes sense on most other levels.

TOP 3 C6 DEALS

The results below show the top C6 deals on buyacar

	Citroen C6 2.2 HDi 16V 4dr Saloon
	ETR	Mthly £521	Saving £1,332	Price £27,093
	Citroen C6 2.2 HDi 16V Lignage 4dr Saloon
	ETR	Mthly £580	Saving £1,518	Price £30,007
	Citroen C6 2.2 HDi 16V Exclusive 4dr Saloon
	ETR	Mthly £646	Saving £1,710	Price £33,015

typical 9.83% APR

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