MERCEDES-BENZ has introduced its upgraded SLK roadster at the same time as its facelifted big brother, the SL.

The German luxury-car manufacturer claims it has changed 650 components as part of the facelift, with the most important upgrades being made to its four and six-cylinder engines.

The 3.5-litre V6 is the same as the one that serves in the new SL350, which means it runs a higher compression ratio, revised pistons and associated components as well as a new intake manifold to increase the rev limit to 7200rpm.

This boosts power by 24kW to a handy peak output of 224kW, while torque increases by 10Nm to 390Nm. That allows the new SLK350 to dash from 0-100km/h in just 5.4 seconds, which is 0.2 seconds faster than the previous model.

It does this even though it, and the SLK200 Kompressor, now feature a longer final drive ratio designed for fuel-economy gains.

Mercedes also says it has done a lot of work tuning the 3.5 V6 to produce a more emotive note. It is available with either a standard six-speed manual transmission or an optional seven-speed automatic.

Using the manual, the new SLK has a combined fuel-consumption figure of 9.5L/100km which is down by a massive 2.3L/100km. The SLK350 uses 9.2L/100km when fitted with the automatic, which is 1.9L/100km less than before.

The entry-level SLK200 Kompressor has also been given a boost and now produces 15kW more power for a total of 135kW, while torque increases by 10Nm to 250Nm.

Its fuel consumption has dropped by 1.2L/100km to 8.0L/100km.

Available with a six-speed manual transmission or a five speed automatic, the SLK 200 Kompressor manages the 0-100km/h dash in 7.6 seconds (manual).

Mercedes decided against upgrading the AMG SLK model. While most other Mercedes models now run the new 6.2-litre V8, the AMG SLK continues to run a 5.5-litre V8 that produces 265kW and 510Nm and is linked to a seven-speed automatic.

Even so, the SLK55 is still a quick machine, running from 0-100km/h in just 4.9 seconds. The new SLK runs a new ‘direct-steer’ system, created by Australian company Bishop Steering, which combines a variable steering ratio with speed-sensitive assistance which Mercedes says results in a more agile steering feel.

It also means there is a reduction in required steering angle at low speeds. Mercedes says the number of steering wheel turns from lock to lock is reduced by around 25 per cent with the new system.

Like its SL sibling, the SLK has also been given an external facelift, with a new front bumper and airdam that incorporates an aggressive V-shape in the bottom edge.

There are also new ventilation grilles and fog lights with chrome surrounds.

The revised SLK features a new rear diffuser, trapezoidal tailpipes and darkened tail-lights. There are larger exterior mirrors with LED indicators and a new range of light-alloy wheels.

Mercedes has upgraded the interior with a new three-spoke steering wheel and a new instrument cluster. A new “gullwing” red interior treatment is now available, while beige nappa leather is new, as are two woodgrain trims.

There is also a new NTG 2.5 audio system with hands-free phone connectivity and iPod compatibility, while Linguatronic voice control is now an option.

Mercedes has also included the Airscarf system, which blows hot air onto the necks of the occupants through the back of the seats, as standard on the SLK350 and SLK55 AMG.

It is available as an option on the SLK200 Kompressor.