What was the engine type of the 1991 winning Mazda 787B?

The 1991-winning Mazda 787B used a rotary engine.

Its powerplant was Mazda’s R26B, a naturally aspirated four-rotor Wankel engine. Unlike a conventional piston engine, the Wankel uses spinning triangular rotors inside specially shaped chambers to produce power. In the 787B, the engine was officially listed at roughly 2.6 litres under contemporary racing conventions and produced about 700 horsepower in race trim.

The rotary design helped Mazda pursue compactness, smooth power delivery and endurance reliability. The R26B also used peripheral intake ports, variable-length intake trumpets and three spark plugs per rotor. Those details improved breathing and combustion while keeping the engine suitable for a 24-hour race.

“Rotary” is the broad, canonical answer; “Wankel” or “four-rotor Wankel” is the more technical description. The engine did not have a V-shaped or inline piston-cylinder layout, so V8, V10 and inline-4 are all clearly wrong. The 787B remains the only car with a non-reciprocating engine to win Le Mans outright.