BMW has bolstered its 1 Series baby with the most economical model to wear the propeller badge in Australia.

The $46,790 120d Sport Hatch is also the first manual-transmission diesel-powered BMW the firm has ever offered over here.

It also debuts the auto idle/stop fuel-saving technology as part of BMW’s EfficientDynamics drive.

These, along with a number of other innovations, help the six-speed manual 120d to achieve 4.8 litres per 100 kilometres average fuel consumption, as well as a carbon dioxide emissions rating of 128g/km.

Under the bonnet is a common-rail injection 2.0-litre single turbo-diesel engine delivering 130kW of power at 4000rpm and 350Nm of torque at 1750rpm.

Also available with the ZF six-speed automatic Steptronic gearbox for $2200 extra, this is the third engine upgrade the hitherto automatic-only 120d has received since the diesel 1 Series was launched in Australia in May 2006 as a 115kW/330Nm model.

A 10kW/10Nm upgrade arrived with the E87 facelift from March 2007.

With a zero to 100km/h sprint-time of 7.6 seconds, the 120d manual is billed as the performance diesel hatch, since the 105kW/300Nm 118d that is arriving in November will be headline eco warrior of the range.

It may be 1.4 seconds slower than the 120d, but the $42,170 118d returns 0.3L/100km better economy and 9g/km less CO2 than its bigger brother, matching the considerably slower (though $3270 cheaper) 77kW/250Nm Audi A3 TDI e.

Furthermore, the $50,790 123d Sport Hatch will steal the 120d’s performance crown in November, with a 150kW/400Nm 2.0-litre twin-turbo engine that is capable of propelling the hatch to 100km/h in seven seconds flat, while offering 5.2L/100km on the EU cycle.

The latest EfficientDynamics measures found in the 120d (as well as the 118d and 123d) include air vents that automatically open and shut to reduce air resistance, electric power steering that does not labour the engine like the old hydraulic set-up, an optimum gearshift indicator that ‘teaches’ the driver the best times to change gears, and brake energy regeneration, which uses spare kinetic energy through deceleration or braking to charge the battery.

Most of these were implemented as running changes in the 1 Series from March 2009 production at the Leipzig plant in Germany, and build on the existing efficiency technologies found in some other BMWs such as high-precision injection, lightweight construction and advanced aerodynamics.

Standard features in the 120d Sport Hatch include ESC, rear parking radar, cruise control, automatic climate control, sports seats, 17-inch alloy wheels with runflat tyres and a leather-wrapped steering wheel with multifunction buttons.

It also is available with BMW’s M Sport Package, satellite navigation and adaptive Bi-Xenon HID High Intensity Discharge headlights, among a long list of other options.

Partly spurned by the federal government’s tax break for vehicles that achieve less than 7L/100km, the 120d manual will be joined by another 10 new EfficientDynamics diesel 1 Series hatch, Convertible and Coupe models by the end of the year, with more expected during 2010.

The company has also announced that it is increasing the number of 320d 3 Series models to include the Touring wagon, convertible and coupe, while the recently released 330d six-cylinder turbo-diesel sedan will receive a coupe and convertible stablemate by the end of the year.

BMW launched the E87 five-door hatch in Australia in October 2004, and it is closely related to the E90 3 Series that followed it from May 2005.