When the 911 Carrera isn't hot enough, the Turbo turns up the heat.

Development of the Porsche 911 Turbo continues at the Nürburgring. This video catches a camouflaged test prototype for 10 minutes as it laps the Nordschleife and stops by a nearby petrol station. The clip provides a great chance to see the new coupe's performance capability and offers an up-close look at the exterior design details.

The new 992 generation of the 911 Turbo reportedly uses an updated version of the existing model's twin-turbo 3.8-litre flat-six engine. The tweaks allegedly mean that the standard model makes around 600 horsepower, and the hotter S variant possibly packs upwards of 640 bhp. Instead of the current seven-speed dual-clutch gearbox, the new Turbo might use an eight-speed DCT like the standard 911 Carrera. The output would still run through an all-wheel-drive system to make the job of handling the power a little easier for drivers

Aesthetically, the biggest differences for the new 911 Turbo versus the standard 911 Carrera are mostly at the back. There are air intake inlets in the rear wheel arches and there's a more traditional looking active rear wing rather than the panel that tilts upward on the lesser model.

We expect the 911 Turbo to debut before the end of the year. In all likelihood, look for the model to be on display at the Frankfurt Motor Show in September. An online debut could arrive even sooner, though. Later, spy shots tell us that a convertible variant is on the way, but expect its arrival to be several months after the hardtop.