As reported before, the next Z4 will feature a retractable hard top, but a cloth roof will continue to be offered on entry-level models. Motivation will come in several different flavors, beginning with naturally aspirated four- and six-cylinder powerplants. A diesel is also being considered – a first for the Z4 – and there's no doubt that the 3-series-based roadster will come packing the twin-turbocharged, 3.0-liter inline six that's proliferated throughout BMW's lineup. More importantly, rumors are beginning to swirl that the M version will be equipped with the 4.0-liter V8 currently found in the M3. If that happens, it's all but guaranteed that the twin-clutch gearbox will find a happy home in the transmission tunnel.