PORSCHE is billing them as 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.

They are available in both coupe and convertible body styles with the twin-turbocharged, 3.8-litre engine in the 911 Turbo version now boasting 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. Basically, 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 subsequent pressure on the accelerator pedal – with the effect more pronounced in Sport and Sport Plus modes.

As for performance the 911 Turbo S Coupe can soar to 62mph from a standing start in just 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, an increase of 3mph.

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

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