BIG six-cylinder performance combined with small four-cylinder fuel economy and ‘best in segment’ dynamics are the touchstones of BMW’s latest diesel debutante. Priced from $56,700, the E90 320d is around $3300 more expensive than its petrol-powered equivalent.

It is also the first 3 Series, as well as the fifth BMW, to gain diesel power in Australia. From earliest to latest, the X5 3.0d, X3 3.0d, 530d and 120d preceded the 320d.

Like Mercedes’ $68,900 C220 CDI and Audi’s $56,990 A4 2.0 TDI, BMW is only offering the 3 Series in a four-door sedan bodystyle – for now.

As in the 120d, outputs from the longitudinally-mounted 1995cc twin-cam 16-valve four-cylinder common-rail direct-injection turbo-diesel engine are 115kW of power at 4000rpm and 330Nm of torque at 2000rpm.

In contrast, BMW’s 1995cc 2.0-litre four-cylinder petrol-engined 320i offers 110kW at 6200rpm and 200Nm at 3600rpm, while the Mercedes delivers 110kW and 340Nm and the Audi 103kW and 320Nm.

BMW’s own six-cylinder 190kW 330i manages ‘only’ 300Nm.

Drive in both 320s is relayed to the rear wheels via a ZF six-speed Steptronic sequential-shift automatic gearbox. No manual is available in the diesel.

The E90 sedan’s MacPherson strut aluminium double-joint front axle and MacPherson strut five-arm rear axle suspension set-up remains for the 320d, as does the rack-and-pinion steering system.

Sharing the same 84mm x 90mm bore and stroke as the petrol engine, the diesel unit has a compression ratio of 17:1, uses a second-generation common-rail injection with a 1600-bar pressure pump, and employs an exhaust gas turbocharger with variable turbine geometry.

Aided by a power-to-weight ratio of 12.6kg per kiloWatt, the 1445kg 320d sprints from standstill to 100km/h in 8.9 seconds - 0.6 seconds swifter than the 1390kg 320i auto. Also, at 216km/h, the diesel’s top speed is 1km/h faster.

Yet the 320d’s 6.7 litres per 100km fuel consumption average eclipses the 320i auto’s 7.9L/100km-result, while a 5.3L/100km highway figure translates to a 910km range from the 61-litre fuel tank. The city cycle shows 9.1L/100km.

Similarly, diesel outdoes petrol-auto by delivering less carbon dioxide emissions – 179g/km versus 190g/km. Both engines are Euro IV-pollution compliant.

However, the 320d’s fuel-consumption average cannot quite match the Mercedes (6.6L/100km) or Audi (6.4L/100km).

Like the 320i, BMW is offering the 320d in base and Executive models.

Both include stability control, anti-lock brakes and a trio of safety-related BMW acronyms (DBC: Dynamic Brake Control, CBC: Cornering Brake Control and ASC+T: Automatic Stability Control and Traction).

Six airbags, cruise control, climate control air-conditioning, Bluetooth mobile phone preparation, CD audio, rain-sensing wipers, auto-on/off headlights, remote central locking, a ‘multi-function’ steering wheel and DataDot technology are also standard.

As with every E90, runflat tyres (205/55 R16), with pressure indicators and a 250km range (at an 80km/h maximum speed) are incorporated, eliminating the need for a spare wheel and jack.

The 320d Executive adds more leather upholstery, alloy wheels, fog lights and an enhanced lighting package.

An extensive options list is available, including BMW’s controversial Active Steering system, bi-Xenon adaptive headlights, satellite-navigation, heated seats and automatic cruise control, along with a $5500 M Sport bodykit and cabin enhancement.

BMW Australia may be optimistic about the 320d’s chances of success, but it is being extremely conservative with numbers.

It expects to sell around 280 sedans first full year, accounting for around seven per cent of all 3 Series sales. Most are expected to be conquest sales from rival offerings, with more males than females settling for the diesel.

Interestingly, Volkswagen also forecast seven per cent for diesel when the Golf V range was introduced to Australia in 2004. Today one in two Golfs sold is diesel.

BMW Australia is also being coy about the appearance of a 320d Touring wagon. GoAuto believes such a variant is at least one year away, if at all. The Bavarian company is watching the Australian market’s reception for the sedan and 323i Touring very closely.

Abroad, critical reaction to the 320d has been extremely positive, with one publication calling it the best car in the world.