PORSCHE is calling them the ultimate 911 models and when the new Turbo and Turbo S stablemates hit UK streets in January they will come with more power and a sharper design.

The dynamic duo make their public debut a couple of weeks earlier at the Detroit Motor Show and the German manufacturer says these everyday supercars will be even more user friendly than before.

Available in both Coupe and Convertible versions, the twin-turbocharged, 3.8-litre flat-six engine in the 911 Turbo now has an output of 540bhp while the Turbo S has been boosted to 580bhp.

And the engines now have what is known as a ‘dynamic boost function' to further raise engine response.

It works by maintaining the charge pressure during load changes, such as when the accelerator pedal is released briefly, by just interrupting the fuel injection, whereas the throttle valve remains open.

The upshot is that the engine reacts with practically no delay to a subsequent press of the accelerator pedal - with the effect more pronounced in Sport and Sport Plus modes.

As for performance the 911 Turbo S Coupe can blast from 0-62mph in a fleeting 2.9 seconds while its top speed of 205mph is 8mph higher than before.

In the case of the Turbo the figures are 0-62mph in 3.0 seconds with a top speed of 198mph - up by 3mph.

Nonetheess, the coupes only consume a Combined 31mpg and the convertibles 30.4mpg, a gain of approximately 2mpg for all versions.

Sport Chrono Package with Mode Switch and Sport Response button will now be a standard feature for both derivatives, as will the new GT sport steering wheel from the 918 Spyder.

It features a rotary mode switch for selecting one of the four modes - Normal, Sport, Sport Plus or Individual.

New options for all 911 Turbo models include the radar-based lane change assist and a lift system for the front axle that can be used to increase ground clearance by 40mm at the front spoiler lip at low speeds.

Prices see the 911 Turbo Coupe costing £126,925 (£135,766 Cabriolet) and £145,773 for the Turbo S Coupe (£154,614 Cabriolet).