AMG's third high-performance small car has been spied undergoing testing at the Nurburgring. While the high-performance version of Mercedes' upcoming baby SUV isn't due out for another year or so, the GLA is rumored to be making an appearance in concept form at next week's Shanghai Auto Show before its formal reveal at the 2013 Frankfurt Motor Show in September. Powering the GLA45 AMG is the Affalterbach tuner's 2.0-liter turbo four that first debuted in the A45 AMG and later in the CLA45 AMG.

Utilizing direct injection, a twin-scroll turbocharger and the cooling system from the SLS AMG, the engine produces 360 horsepower and 332 lb-ft of torque to emerge as the most powerful production four-cylinder engine in the business. It shifts the A45 and CLA45 from 0-62 mph in 4.6 seconds, and while the taller GLA may slow that number slightly, it should be on a similar pace - and that's quite a rapid pace indeed.