AMG's 469-hp M139 four-cylinder is the most powerful of its kind, but the C63 S E Performance failed commercially and is being replaced. For decades, Mercedes-AMG has built its reputation on thunderous V8 engines that transformed ordinary Mercedes-Benz models into tire-smoking autobahn missiles. That's a little ironic, though, because AMG has never been a V8-only brand. Over the years... [7915 chars]