► Mid-life update for the Porsche 991

► Spotted completely free from disguise

► Prototype features unusual central exhausts

Here’s our best look yet at the facelifted Porsche 911, spied testing without a spec of camouflage ahead of its September debut at the 2015 Frankfurt motor show.

Porsche 991.2: those styling updates in full

Unsurprisingly, there’s no radical departure from the established 991 script here. This is a subtle brush-up, with new headlight units incorporating thin bracket-shaped LED daytime running lights, and a similarly thin strip arrangement for the tail-light graphics.

There’s a little of the recently introduced Cayman GT4 in the outer grille treatment on the new front bumper and the engine cover’s now topped with a different, rather retro vent treatment. 'Spot the difference' champions might have clocked the altered door handles, too.

Though we can’t see much of it here, the interior will get a refresh too with a new steering wheel and updated infotainment system with improved connectivity.

A turbocharged future for the Porsche 911

Big news for 991.2 lies beneath those new engine vents. As CAR revealed in October 2014, the 911’s famous flat-sixes are about to shrink in size and grow turbochargers in an effort to curb fuel consumption and emissions while boosting power.

From launch there will be two models offered, both packing twin turbos: a 2.7-litre Carrera with 370bhp, and 3.0-litre Carrera S with 420bhp. Both will offer a big jump in torque and fuel economy savings tipped to be in double digits compared with their equivalent 991 forerunners. As for whether they’ll offer the same spine-tingling soundtrack and precise throttle response, we’ll have to wait and see.

This doesn’t mean total extinction for 911s without forced induction – the next-gen GT3 will stay naturally aspirated, initially using an evolution of its current 4.0-litre engine before being replaced by a lighter, more powerful MkII engine – which, crucially, is expected to remain without forced induction.

As for the 911 Turbo, it’ll stick with the current 3.8-litre unit, which will grow in power to 600bhp in the facelifted 911 Turbo S.

Could this particular prototype point towards a new back-to-basics model?

The blue car pictured here sports centrally mounted exhaust outlets, a point which has intrigued trackside observers. Rumours abound of a pared-back driver-focussed model in the pipeline, potentially to be named the 911 GT. This blue prototype is thought to be an early iteration of just such a model. The seats are thin leather buckets rather than the usual racing seats fitted to many track-bound prototypes. Don’t be misled by the rollcage – many prototypes subjected to hard track work are fitted with cages for safety.

The same central exhaust layout has been spotted on all three 911 body styles, coupe, convertible and Targa, though so far only this coupe has been spotted without camouflage.

Porsche 991.2 scheduled for Frankfurt show debut

Following its official reveal at the 2015 Frankfurt show in September, the 991 is scheduled to go on sale later in autumn 2015. It will remain in production until it's replaced by an all-new 911 scheduled for autumn 2018, based on a new chassis with components that will be shared across the wider Porsche/VW group.