The new Porsche 911 is a supercar with a conscience as it improves fuel economy and lowers emissions.

While the power of the 3.6-litre engine grows by 20bhp and the 3.8-litre by 30bhp, both now use less fuel.

The 3.6-litre engine returns 1.60 km per litre, while the larger unit manages 1.65 km per litre, which are both improvements over the cars they replace.

For both engines, Porsche has reduces carbon dioxide emissions by 15%, even though top speed has now gone up to 186mph.

A new double-clutch gearbox will feature in the new 911 for the first time.

This seven-speed gearbox uses two clutches to give lightning quick manual changes without the need for a clutch pedal.

The driver uses paddles mounted behind the steering wheel to change gear, just like in a Formula One car.

Using this gearbox, the 911 sprints from 0-100 km per hour in 4.5 seconds, which is 0.2 seconds faster than the standard six-speed manual version.

Changes to the exterior are much more subtle and include new daytime running lights.

There's also the option of headlights that help the driver see further round corners.

The new 911 goes on sale later this month and prices will see small rises on all models.