MAZDA'S important mid-size competitor, the Six, has been refreshed in the face of sizzling competition in a booming segment that is eclipsing the large-car market.

The Japanese company claims to have made more than 750 engineering changes to the car, concentrating on improving refinement, lowering noise, vibration and harshness levels as well as improving fuel consumption.

The smooth 122kW/207Nm 2.3-litre four-cylinder carries over but now boasts an electronic throttle and lower exhaust emissions that make the car Euro IV-compliant.

The engine revisions and adoption of a six-speed manual or five-speed sequential "Activematic" auto have resulted in modest fuel economy gains.

As a result, prices have risen slightly, between $550 (for the Limited sedan) and $1110 (for the Luxury Sports). The volume-selling Classic model is $590 more expensive.

The five-speed automatic is a $2000 option on Limited, Classic and Luxury Sports models and standard on the Luxury and Classic wagon.

Visually, the car gains some external tweaks to bumpers, the grille, tail-lights, along with new alloys. Some modest interior trim changes are included as well.

The basic suspension configuration carries over, comprising a double wishbone front-end and multi-link rear. New bushings and retuned spring and damper rates are designed to offer better balance between handling and ride comfort.

Mazda claims the body is stiffer, and therefore safer, through extra reinforcing around the body, B-pillars and floor. The extra beef has added between 3-4kg to overall weight.

Customer feedback on interior noise levels has also resulted in better sound insulation in a claimed 18 areas around the cabin.

Standard equipment levels have also improved.

The entry six-speed manual Limited sedan offers air-conditioning, a four-speaker CD stereo, remote central locking, electric windows/mirrors, driver's seat height adjustment, 15-inch steel wheels, reach and height-adjustable steering and an outside temperature gauge.

The Classic sedan and hatch add climate-control air-conditioning, 16-inch alloys, a leather-clad steering wheel, trip computer, foglights, six-stack six-speaker CD stereo, steering wheel-mounted audio and cruise control, and more lavish interior trim.

The Luxury sedan and hatch ups the ante further with 17-inch alloys, standard auto, sunroof, leather seats, seven-speaker Bose sound system and an electric driver's seat with memory.

For another $1010, the Luxury Sports hatch offers a bodykit, straight-through twin exhausts and alloy pedals.

All Mazda6 models feature six airbags and anti-lock brakes with electronic brake-force distribution. Other safety items include a breakaway brake pedal and anti-whiplash front head restraints.

Mazda Australia managing director, Doug Dickson, said the Six had the credentials to maintain its lead against other mid-size contenders like the Euro-inspired Hyundai Sonata V6, Honda Accord Euro, Holden Vectra and Subaru Liberty.

Since its launch three years ago, Mazda Australia has sold 34,000 Sixes - "four times what we sold with the previous model," according to Mr Dickson.

It has maintained a sales rate around 1100 a month, 83 per cent more than Mazda's initial forecast of 600 sales a month.

In the medium-car segment, it trails Toyota's market-leading Camry four-cylinder by 16.7 percentage points, but is well entrenched in second place.

Since its launch sales have been split nine per cent Limited, 54 per cent Classic, nine per cent Luxury and an impressive 28 per cent Luxury Sports.

Mr Dickson said he was surprised by the success of the most expensive model, which he believes was a preference for many user-choosers who would have previously opted for a Volkswagen Passat or Peugeot 407.

Overall, the hatch has been the most popular model, representing 52 per cent of sales with most buyers opting for the five-speed automatic.

Mazda is forecasting sales of 1150 a month.

The new turbo-charged, all-wheel drive Mazda6 MPS arrives in October, a month later than expected. Mazda says dealers are already holding a strong order-bank for the $50,000 sports sedan but expected supplies to be limited. The company is expecting to sell about 100 a month, with the luxury pack version costing $55,000.