Written by Gerry Martselos
Introduction
The rotary engine has never been fully understood by the general public. What is not understood is generally not accepted, and as a result the rotary remained within a cult following for most of its existence. Those who do understand it tend to become fanatical — to the point of addiction. If the RX-7 has caught your eye, browse Mazda RX-7s currently for sale on JDMBUYSELL to see what's on the market.
The rotary is commonly used in aircraft, and as most car enthusiasts know, Mazda built rotary-powered sports cars for decades. The concept rests on a deceptively simple principle:
Use the rotational momentum of the engine instead of fighting against it.
How a Conventional Piston Engine Works
A typical internal combustion engine mixes air with fuel, compresses that mixture, and ignites it to produce an explosive force. That force is contained in a cylinder; during the combustion stroke, a piston transmits it to the crankshaft through a connecting rod. Add the valvetrain on top of that, and you have a design with hundreds of moving parts.
The stationary combustion chamber demands valves that open and close precisely — letting the air-fuel mixture in and exhaust out, then sealing tight during compression and combustion. It works, but it is complex by necessity.
A Better Way: The Wankel Rotary
If the goal is to compress air and fuel into a container and ignite it, there is a more elegant path. With a rotary engine, intake and exhaust "valves" are built directly into the engine's geometry — no valvetrain required.
As the triangular rotor sweeps around the epitrochoidal housing, its three faces pass across intake and exhaust ports cut into the housing walls. The rotor's position opens and closes those ports exactly when needed. The shape of the ports determines how long they stay open. It is a mechanical solution that replaces an entire sub-system with the rotation itself.
Inside the housing, combustion does not happen in a cylinder. As the rotor compresses the air-fuel mixture against the housing wall, two spark plugs ignite it. The expanding gases push against the rotor face, which applies force to the eccentric shaft — and that is how power is made.
Why the Rotary Can Rev So High
The rotary's reputation for high-revving capability comes down to one key geometric relationship: the output shaft rotates at three times the speed of the rotor, courtesy of the engine's cycloidal gearing.
There are no pistons being forced to accelerate and decelerate at extreme speeds, and no valvetrain to "float" open at high rpm. The rotor itself moves relatively slowly — when the output shaft is turning past 9,000 rpm (not recommended for street use), the rotor is only turning at a leisurely 3,000 rpm. The engine delivers high shaft speeds while keeping the internal moving mass at one-third that pace.
The Dual-Rotor Layout
The twin-rotor design used in the RX-7's 13B engine is optimal for balance. The two rotors are phased against each other so their power pulses counteract vibration, producing a notably smooth power delivery despite the engine's compact dimensions. Each rotor completes one power stroke per revolution, giving the 13B a power stroke every 120 degrees of eccentric shaft rotation — more frequently than a comparable four-cylinder piston engine.
A dedicated metered oil-injection system lubricates the apex seals (the rotary's equivalent of piston rings), which are the most wear-sensitive components in the engine.
Multi-Rotor Configurations
If more cylinders improve a piston engine, the same logic applies to rotors. Mazda experimented with three- and four-rotor engines throughout its motorsport program. The four-rotor architecture proved the concept's ultimate expression in competition.
The Rotary in Racing: Mazda 787B
Mazda built an impressive record of victories with rotary-powered race cars. The highlight came in 1991, when the four-rotor Mazda 787B became the first Japanese manufacturer ever to win the 24 Hours of Le Mans. The 787B's R26B engine — a naturally aspirated four-rotor producing around 700 hp — remains one of the most distinctive-sounding racing engines ever built.
That result demonstrated what the rotary's combination of compact size, light weight, and high power density could achieve at the highest level of endurance racing.
The Bottom Line
The Wankel rotary is not a curiosity — it is a legitimate alternative to the piston engine, one that trades the complexity of valve gear and reciprocating mass for a geometry that is inherently rotational. Its weaknesses (apex seal wear, fuel economy, emissions at cold start) are real, but so are its strengths: extraordinary power density, mechanical simplicity, and a rev ceiling that piston engines of comparable displacement simply cannot match.
For anyone who spent time with an FD3S RX-7, those strengths were always the point. If you're considering owning one, JDMBUYSELL's RX-7 model guide covers what to look for when buying, common issues with the 13B, and how importing to the USA works for vehicles like this.