M291

For 1991 the FIA scrapped Group C’s turbo formula in favor of 3.5-liter naturally aspirated engines built to Formula 1 rules. Jaguar lifted Ford’s Cosworth HB straight out of a Benetton; Mercedes-Benz had nothing that fitted and began on paper. Race engine director Hermann Hiereth laid out a 180° twelve — opposed rather than a true boxer, with two connecting rods on each crankpin — and took the drive from the center of the crankshaft to damp torsional vibration, which allowed the six-speed gearbox to sit transversely and high and leave the underfloor venturi clear. TAG supplied the management, and with it live telemetry to five screens in the pit garage.

It began at 550–600 hp against the 730 of the twin-turbo V8 in the C11 it replaced, weighed a stubborn 170 kg, and spent the season losing oil-scavenging arguments with itself. Twelve throttle butterflies in place of four, lighter internals and reworked pumps took it to roughly 640 hp at 13,200 rpm, and close to 690 by the end of the year. Michael Schumacher and Karl Wendlinger then won the season finale at Autopolis with it. Mercedes-Benz shut the sportscar program soon afterwards, and the flat-12 retired on that single victory.