Here are the latest spy shots of a virtually undisguised next-generation Porsche 911 having itself a winter workout in the Scandinavian wilderness. Porsche is still hiding some of the rear details of the new model but our spy photos provide a general idea of what's in store for the new back-end design.The next 911 will be 4.49m long, 56mm more than the current model, with 10mm extra wheelbase. The car will also stand 11mm lower.Under the bonnet the 3.4-litre entry-level Boxer engine (down from the 3.6-litre unit) has an output of 257kW and, with a top speed of 289km/h, is capable of completing the 0-100km/h sprint in 4.8 seconds. The smaller, more-efficient unit will reduce fuel consumption by 13% to 8.5 litres/100km.The Carrera S will receive a revised 3.8-litre unit capable of 294kW. The revised engine will enable the Carrera S to rocket from 0-100km/h in 4.5 seconds and produce a top speed of 302km/h.Fuel consumption will decrease by 14%, Porsche says, to 9.1 litres/100 km.