The Rotary Engine: Mazda's Unconventional Bet That Won Le Mans

The internal combustion engine in virtually every car uses pistons that move up and down in cylinders. It is a reciprocating motion -- linear movement converted to rotational output via the crankshaft. The mechanism works, but it carries inherent compromises: back-and-forth mass, vibration to manage, and mechanical complexity just to convert one type of motion into another.

The Wankel rotary engine, named after its inventor Felix Wankel, discards all of that.

How It Works

Instead of pistons, a rotary engine uses a triangular rotor -- a rounded triangle with slightly curved sides -- that orbits inside a housing shaped like an epitrochoid (an oval figure-eight). As the rotor turns, each of its three faces traces a path around the housing, creating three separate chambers that continuously change volume.

These volume changes drive the four strokes of the combustion cycle -- intake, compression, combustion, exhaust -- but they happen simultaneously in different sections of the housing rather than sequentially in one cylinder. The result is a power stroke every 270 degrees of rotor rotation, compared to every 720 degrees in a four-cylinder piston engine.

Because the rotor moves in one continuous direction rather than reversing, a rotary engine has almost no reciprocating mass. Vibration is dramatically reduced. The engine can rev higher. Power-to-weight ratio for a given displacement is excellent.

The Challenges

The tips of the rotor -- the apex seals -- must maintain a gas-tight contact with the housing throughout the rotor's orbit. These seals are under significant stress, and their failure was historically the rotary engine's main weakness. Oil consumption is also higher because the design requires a small amount of oil injection for lubrication.

Emissions certification has become increasingly difficult as regulations have tightened. This is a primary reason Mazda discontinued the RX-8 in 2012 despite a loyal following.

The Racing Record

The rotary engine has one achievement no other engine architecture can claim: Mazda's 787B won the 24 Hours of Le Mans in 1991. It is the only rotary-powered car ever to take an overall win at Le Mans, and the only Japanese manufacturer win in the race's history.

The four-rotor engine produced approximately 700 hp and ran through the night without mechanical failure. The sound it produced -- a high-pitched scream distinct from any piston engine -- remains one of motorsport's most recognisable sonic signatures.