Mercedes C-Class

Controversially, the unit is a V6 diesel, and it is the first small-capacity V-formation oil-burner the firm has made. Set to power the forthcoming R-Class luxury MPV and S-Class, as well as future editions of the SL, SLK and E-Class, it's hard to imagine the consequences if the engine isn't up to scratch.

Replacing the impressive straight-six unit which we experienced in the E320 CDI last week (Issue 843), the V6 makes its debut in the new C320 CDI. Aimed at BMW's latest 3-Series and Audi's A4, the new machine promises to be the most powerful and economical car in its class.

Backing these claims is advanced technology which boosts muscle and fuel-sipping ability without harming emissions. The Merc delivers 224bhp and a massive 510Nm, and combined with the optional seven-speed auto box, it gives incredible acceleration.

Maximum torque is available at 1,600rpm, so overtaking requires only the lightest touch of the throttle. Flat-out, the car will hit 0-62mph in 6.9 seconds. Top speed is limited to 155mph, which underlines its sporting saloon credentials.

The performance does not come at the expense of refinement, though. At idle or when cruising, the engine is quiet and smooth. Even when extended, the diesel unit emits a pleasing thrum. Economy also impresses, with acombined figure of around 36mpg giving a competitive blend of performance and frugality.

The new diesel engine is a perfect partner for the Sport package. This gives the car an AMG bodykit as standard, including a discreet rear spoiler, which brings out the best features of the C-Class shape. Colour options are restricted to silver or black. The 17-inch alloy wheels wrapped in wider tyres look better and provide more grip - essential with the amount of torque available.

Sport editions also have a firmer suspension set-up, which improves body control without paying a significant comfort penalty. Despite the bigger wheels, the C-Class retains its good ride quality, but the Sport brings competitive handling.

The interior also benefits from the racy treatment. The three-spoke steering wheel is pleasant to hold, while the silver-faced dials boost the cabin's appeal. Standard sports seats provide good comfort as well as side support. The Sport edition is a welcome addition to the C-Class range, bringing extra equipment for a competitive price. The real star of the show, however, is the diesel engine. This new motor combines genuine performance with refinement and economy, which makes this Mercedes a fine all-rounder.