Two prototypes spied testing on the Nürburgring - one in red and one in black. SLK AMG model may debut in the fall.

More spy photos coming to us from testing on the Ring, this time of the 2012 Mercedes-Benz SLK AMG.

Caught here are two prototypes, one in black and one in red, with less camouflage than in previous spottings, given that the standard SLK model has already been debuted.

As for power plants expected, there are three possiblities: a normally-aspirated 422 bhp (315 kW / 428 PS) 5.5-liter V8, a 451 bhp (336 kW / 457 PS) 6.2-liter V8, or a detuned version of the 5.5-liter twin-turbo V8 that normally produces 537 hp (400 kW / 544 PS) and 800 Nm (590 lb-ft) of torque.

We'll just have to wait and see. The model may make a debut at the Frankfurt motor show in the fall.

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