As we've said before, Mercedes in-house speed shop AMG adopted a multitiered approach to tuning. At the second tier from the top Signature series, the Black Series includes uprated and spec'd out versions of AMG models. We've already seen the CLK63 Black Series, which sports a 500-horsepower version of the AMG 6.2-liter V8 (dubbed 6.3 for historical purposes). Now, a prototype of what looks to be the SL-Class AMG Black Series model was recently spotted in preparation for Nürburgring runs this week. The Black Series cars are lightened by way of carbon fiber replacement panels and made nimbler by way of an adjustable suspension with modified spring links, wheel carriers, thrust arms and camber and torque struts. The CLK63 can get from zero to 60 in a blazing 4.1 seconds. Any guesses on this track-day monster? [Winding Road]

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