In 1991, a rotary-powered Mazda won the 24 Hours or Le Mans. By 1992, rotary engines were no longer allowed to race there. But for the 2021 season, 30 years after the fact, the organizers behind the biggest race in the world of sports cars have allowed rotaries back in.

This doesn’t come with a big announcement. Don’t look for news articles on the Le Mans or FIA websites heralding the return of the engine that goes hmmm. Don’t look for anything on Mazda’s site either. Nothing there.

But tucked away in a subsection of the recently released is a little line about rotaries. I didn’t notice it until race car tech super-knower off a linked article from :

NSU even gets a shout-out:

Rotaries were initially banned out of Le Mans as Group C in the 1980s transitioned into the 1990s to share the same engine regulations with Formula 1. That meant naturally-aspirated 3.5-liter piston engines.

Doing so .

Group C was one of the greatest eras in racing history, producing the fastest cars to ever run the…

Not the best.

But now rotaries are allowed in again. Here’s every line about them from the new regs:

The volume swept in the cylinders of the engine by the movement of the pistons. This volume shall be expressed in cubic centimetres. In calculating engine cubic capacity, the number Pi shall be 3.1416.

In the case of a rotary engine, the engine cubic capacity is the volume determined by the difference between the maximum and minimum capacities of the combustion chambers.

[…]

Engine of the type covered by the NSU Wankel patents.

[…]

• Variable geometry devices are not allowed except for rotary engines.

• Engine must not have more than two inlet and two exhaust valves per cylinder.

- Only reciprocating poppet valves with axial displacement are permitted.

- The sealing interface between the moving valve component and the stationary engine component must be circular.

- Electromagnetic and hydraulic valve actuation systems are forbidden.

The engine of the make is a series engine. that meets the following conditions:

• At least 25 identical engines identical to the ones destined for a series production car homologated

for road use equipped with this engine must have been produced;

At least 25 identical series production car

homologated for road use equipped with this engine are produced by the end of the year of the first season this engine is competing in.

At least 100 identical series production car homologated for road use equipped with this engine are produced by the end of the year of the second season this engine is competing in.

The series engine is homologated with FIA/ACO.

One complete engine is deposited with the

FIA/ACO.

[…]

5.8.1 No fuel injectors are permitted downstream of the exhaust valves or of the exhaust port inlet on a rotary engine.

[…]

5.9.1 With the exception of rotary engines, the ignition is only permitted by means of a single ignition coil and single spark plug per cylinder. No more than five sparks per cylinder per engine cycle are permitted.

The use of plasma, laser or other high frequency ignition techniques is forbidden.

[…]

5.14.1 Pistons must respect Article 5.13. Titanium alloys are not permitted. Rotor seals on rotary engines may be manufactured from a ceramic material.

Will Mazda actually come back? Who knows, but I do have my fingers crossed for NSU.