NSU/Mazda Wankel (1967) — no pistons at all

1967·1–4 rotors, epitrochoid housing·2 per rotor·3× rotor speed·Le Mans 1991 (787B)

· THE STORY

The engine with no pistons

Felix Wankel’s engine threw away the piston entirely: a three-cornered rotor orbits inside a peanut-shaped housing, and its three faces wall off three chambers that inhale, squeeze, burn and exhale in turn. NSU put it in the 1967 Ro 80; Mazda made it work and made it sing, from the Cosmo to the RX-7. Tiny, smooth and gloriously revvy, it remains the only engine ever to win Le Mans without a single piston.

1–4 rotors, epitrochoid housingLayout2 per rotorMoving parts

· WHY IT MATTERED

Three faces, four strokes, one orbit

The housing is a mathematical curve — an epitrochoid — that the triangle’s corners ride exactly, at every angle. Each face runs the full four-stroke sequence once per rotor turn, staggered 120° apart, so all four strokes are happening somewhere in the engine at every instant. No valves, no springs, no reciprocating anything: the shaft just turns.

· WHY IT MATTERED

Tiny, smooth, revvy

Two moving parts where a piston four needs some forty. Nothing reverses direction, so there is almost nothing to shake and little to limit revs — a rotary the size of a biscuit tin gave sports-car power and turbine smoothness. The 787B’s four-rotor scream at Le Mans 1991 is still the loudest argument the layout ever made.

· WHY IT MATTERED

The corners killed it

The apex seals at the triangle’s tips scrub the housing at every angle through every temperature — the hardest sealing job in engines. And the long, thin, moving chamber burns its charge badly: thirst and emissions the layout never fully escaped. Mazda retired it in 2012; it returns today only as a small range-extender.

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· TRY IT

Watch the triangle work

The real geometry, live: pause it and scrub the rotor round to follow one face through intake, squeeze, bang and exhaust — and watch the yellow shaft tick turn three times for every turn of the triangle.

Readout

Face A: Intakechamber at 25% of its maximum volume

Moving parts2

Shaft : rotor speed3 : 1

Bangs per rotor turn3

No valves, no springs, nothing reciprocating — which is why it revs so freely and runs so smoothly. The price is at the corners: the apex seals scrub the housing at every angle, the flaw that finally beat the layout.

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