LAKE PARK, Florida — Former AMG stalwart Hartmut Feyhl's RENNtech figured there was plenty of untapped adrenaline under the hood of the Mercedes-Benz C63 AMG — nearly 100 horsepower, as it turns out.Once RENNtech was through fiddling with the car's 6.2-liter V8, output jumped from 451 to 548 hp while torque climbed from 443 to 510 pound-feet. The first step in the transformation was to upgrade the ECU. Then the tuning house added a set of stainless steel long-tube headers and performance-oriented tailpipes.Dig a little deeper under the sheetmetal, and you'll discover a fully adjustable sport suspension that enables the owner to dial in ride height and shock damping settings. The brakes have been upgraded as well.What this means to you: Even without additional modifications, the stock C63 AMG is a veritable bargain at $55,975. — Paul Lienert, Correspondent