The 1991 season marked the introduction of the FIA’s new, and controversial, 3.5 litre formula which replaced the highly successful Group C category that had been used in the World Sportscar Championship since 1982, though due to a small number of entries for the 3.5 litre formula heavily penalised Group C cars (which were subject to weight penalties and started behind the new-style C1 entries on the grid) were allowed participate in the season's C2 category.
To meet the new regulations Mercedes-Benz came up with an all-new car; the C291 which was designed by its racing partner Sauber.
One survived and is on display in the Carl Benz Museum in Ladenburg, Germany.
The primary feature of the new regulations was the use of a 3.5 litre naturally aspirated engine. This made it impossible for Mercedes-Benz to use the engines from its previous Group C cars. Also, to produce similar power to the Group C cars a 3.5 litre naturally aspirated engine had to be very high-revving and be constructed from different materials in order to rev highly.
Unlike Jaguar’s XJR-14 who had the readily available and proven Ford HB V8 engine from the Benetton B190B Formula One car (the engine regulations for the new 3.5 litre formula were identical to Formula One), Mercedes-Benz had to design an all-new purpose-built racing engine and its M-291 3.5L Flat-12 unit was the result. The engine produced about 550–600 brake horsepower (410–450 kW) compared to about 730 brake horsepower (540 kW) produced by 5.0 litre V8 twin turbo found in the C291’s predecessor, the Mercedes-Benz C11.