Expect a limited production run.

The Porsche 911 comes in a variety of flavours, sometimes making it difficult to identify a nondescript prototype. A new batch of spy shots shows us a familiar-looking test vehicle – this isn't the first 911 with a ducktail spoiler we've spotted – but this new one has several distinct differences.

Previous 911 spy shots captured a ducktail-equipped test vehicle sporting a Turbo model's rear haunches, with gaping air intakes puncturing the rear quarter panels. However, the new test vehicle in the latest batch of pics doesn't have those. The wheel arches are smooth, lacking the intakes, but that's not the only difference. A close inspection of the new prototype reveals it sports a double-bubble roof, which isn't present on the other 911 Turbo-like one.

Gallery: Porsche 911 Sport Classic Spy Photos

The front and rear bumpers are also different, with the new test vehicle sporting fascias borrowed from the Turbo S. It also sports centre-lock wheels. Previous rumours suggested that the Turbo test vehicle was a new Sport Classic model, though this new non-Turbo 911 seems like a far better candidate. The previous 911 Sport Classic arrived with a naturally aspirated 3.8-litre flat-six that produced 408 bhp (304 kilowatts) and 310 pound-feet (420 Newton-metres) of torque.

It's unclear what the new test vehicle is sporting for a powertrain, though one likely candidate could be the one that'll power the upcoming 911 GTS model. That car is rumoured to produce around 470 bhp (350 kilowatts) when it arrives, which should be ample oomph for the new Sport Classic.

The new shy shots do leave us wondering what Porsche is doing with the Turbo ducktail model. Porsche has no shortage of 911 variants, so there are several possibilities. If Porsche is developing a new 911 Sport Classic, we expect it to have a limited production run, just like the 2010 model. Porsche limited it to 250 models. We don't expect Porsche to reveal the new model until late this year or early next year.