Currently, Porsche builds two turbocharged 911s – the Turbo and the Turbo S (and their cabriolet counterparts). The rest of the 911 range, meanwhile, is motivated by either 3.4- or 3.8-liter flat-sixes of varying outputs. This clear separation could be set to change in the very near future, though, as rumors continue to swirl that Porsche's rear-engined range could switch exclusively to turbocharged power.
If there's ever been automotive case for constant evolution, it is the Porsche 911. It seems like every time a new version of the rear-engined sports car debuts, Porsche is already hard at work on a facelifted version of it that changes some subtle, barely noticeable aspect.