During the early development of the W140 S-Class, engineers at Mercedes-Benz in Stuttgart explored an ambitious concept: an 8.0-liter W18 engine internally designated the M216. The design used three banks of six cylinders arranged in a compact W configuration and was projected to deliver roughly 490 hp and 750 Nm, with even more powerful multi-valve variants considered on paper. The idea never progressed beyond the prototype stage, as the existing 6.0-liter V12 already provided the refinement and performance expected of the flagship—without the added complexity. Ultimately, the largest engine to reach production in the W140 came via Mercedes-AMG, in the form of the 7.3-liter V12 M297.