By JAMES STANFORD

BMW Australia has launched a higher performance twin-turbo six-cylinder version of its stylish drop-top that is just as fast in a straight line as its M3 poster car.

The awkwardly-named Z4 sDrive35is rolls into BMW dealerships with a recommended retail price of $129,900.

The hot Z4 is capable of blasting from 0-100km/h in just 4.8 seconds, the same time as the manual M3 coupe, but it isn’t an M car.

BMW’s performance arm created an M version of the last generation Z4, stuffing in the contemporary M3’s in-line six.

This time around BMW says it has no plans to produce an M version of the Z4, resisting the urge to try to fit the M3’s V8 under the roadster’s snout. It decided to massage the twin turbo six-cylinder version of the Z4 called the sDrive35i.

It tweaked that car’s 3.0-litre in-like six-cylinder, which runs direct injection and two small turbochargers for the new sDrive35is.

This engine has largely been phased out of the BMW range, replaced by a more advanced single turbo version on all other models.

BMW fiddled with the engine mapping to produce 25kW more power and 50Nm more torque than the sDrive35i, lifting engine performance to a healthy 250kW at 5900rpm and 450Nm of torque all the way from 1500rpm to 4500rpm. An overboost function allows for an extra 50Nm to be brought on stream for short bursts.

BMW says particular attention has been paid to the exhaust tune to ensure it sounds as fast as it is.

The engine is linked to BMW’s dual-clutch automatic transmission which has seven gears and has a launch control function, which helps to explain the super-fast sub five-second 0-100km/h sprint time.

The two-door roadster, which has a metal folding roof, tips the scales at 1525kg – lighter than the M3 coupe at 1600kg.

A more complex version of this transmission is a $7900 option in the case of the M3, but comes standard on the top-shelf Z4. Sadly for some enthusiasts, the manual transmission is not available as an option.

Its suspension architecture is the same as other Z4s, consisting of front struts and an advanced multi-link rear, but the fastest Z4 sits 10mm lower for improved handling and also to make more of an impression.

BMW has fitted it with Adaptive M suspension dampers, which changes the pressure of the fluid in each damper in response to three different settings, Normal, Sport and Sport Plus. It can also react to a bump that affects the front suspension and quickly alter the damping rate of the rear suspension to better deal with it.

Eighteen-inch light allow wheels are standard, as well as an M sport package that includes an aggressive body kit, chunky sports steering wheel, anthracite roof lining, custom aluminium highlights and, as BMW is proud to point out, floor mats with sDrive35is embroidered on them.

It also has the standard features of the next in line Z4 sDrive35i model which includes everything you expect from a luxury model at this price. This means standard leather-trimmed sport seats, leather trimmed dashboard and centre console, keyless entry and start, satellite navigation, adaptive xenon headlights, voice control for many of the features and a premium sound system.

While customers are more likely to care about performance than economy, the sDrive35is Z4 features fuel-saving measures to limit its impact at the pump and on the environment.

The official fuel economy figure is a reasonable 9 litres per 100km/h, which is the same as the less powerful sDrive35i. It has a CO2 emissions average of 210g/km.

BMW says the turbochargers are also as efficient as possible thanks to their resistance to super high temperatures (1000 degrees Celsius). This means there is no need to increase fuel flow to cool them.

The Z4 sDrive35is will go head to head with the 228kW Porsche Boxster S at $131,000, while it may also be shopped against the 224kW Mercedes-Benz SLK 350 at $118,000.

It comes at a premium of $13,001 over the next Z4 model in the range, the Z4 sDrive 35i. BMW Australia says it has been allocated 25 of the new more powerful Z4 sDrive35is models and expects to sell a similar amount next year.