Mazda's RX Vision Concept, which the company promises will be rotary-powered. Mazda Mazda currently has more than 100 engineers working on its next-generation rotary engine, according to a company spokesman.

The engine, a strange, piston-less internal-combustion unit, has defined the brand — largely for a dedicated group of motor-heads — since its first production run in 1965 in the Mazda Cosmo.

Unable to overcome several disadvantages of the engine, including poor emissions, fuel economy, and torque output, the Japanese make ended its usage in 2012, when the RX-8 fell from the lineup.

Many car companies have defining characteristics — Volvos are safe, Toyotas are economical, Minis are, well, mini — but few have stuck to such a specific engineering concept for as long as Mazda. Rotary engines are simply an indelible part of the company.

Research, according to Mazda's Jeremy Barnes, has never stopped, and the company hopes for a breakthrough in the next couple of years.

"There's this incredible passion [for rotary engines] within the company," Barnes said.

And outside the company. Barnes calls their loyal fans "rotor-heads" — people who, like Mazda's engineers, are obsessed with the high-revving, almost vibration-less engines and eagerly wait for their return.

The company revealed the beautiful RX Vision concept car at the Tokyo motor show last year, expecting any future production run of the grand-tourer-style vehicle to be powered by a new rotary called the 16X.

But it's difficult to say when the engineering challenges that killed the previous 13B engine will be overcome.

Upping the displacement from 1.3 to 1.6 liters is one way they hope to add to torque output, but the emissions problem persists. Mazda engineers hope that they can apply years in development of fuel efficiency in piston engines, which they dubbed "SkyActiv" technology, to new rotaries.

But the largest efficiency problem persists because of the fundamental design of rotary engines. Unlike the piston engines found in today's cars, which keep oil out of the combustion chamber, rotaries must also burn oil, making emissions dirtier.

But the road isn't the only place devoid of the rotary.

After the howling, rotary-powered 787B won Le Mans in 1991 — making it the first and only Japanese-made car to do so — the rules were changed significantly, and while rotaries weren't banned outright from racing, regulations made the engines "almost immediately uncompetitive," Barnes said.

While Mazda never stopped racing, its signature engine has been sidelined. But what about a rotary-powered return to endurance racing?

"If we can make a significant breakthrough, it's possible," Barnes said.