Rob Dahm's Billet Four-Rotor 26B Wankel Engine Is a Flame-Spitting One-Off

This high-power build is the first of its kind, and the engineering behind it is immense.

Rob Dahm Four Rotor Billet Wankel Build Oct 2019
YouTube - Rob Dahm

Let’s talk rotary engines. Also known as Wankel engines, these unique power plants can be finicky at best, but when they work, they are absolutely wondrous. Well-known car builder Rob Dahm has been documenting his quest to build the world’s first Billet four-rotor Wankel and after a bit of sorting with the engine’s control units, he started it up for the first time in history, and it sounds otherworldly.

This is a particularly big deal because most Wankel motors consist of only two or three rotors at most. Additionally, while there are several custom shops out there that specially build four-rotor engines, supposedly no one has ever built one with Billet alloy crankcase blocks. When it comes to these engines, Billet Rotary out of Australia is the go-to manufacturer for incredibly durable blocks as they have a reputation for powering some of the fastest rotary-powered drag cars in the world.

Although Wankel engines are common in a variety of applications, from aviation to marine and motorcycles, they’ve only shown up in a few cars. The most notable instances were in Mazda’s renowned RX sports cars, although their engines only consisted of two rotors. The number of rotors is similar to a reciprocating internal combustion engine’s piston and cylinder count.

The most famous case of a four-rotor Wankel-powered car was in Mazda’s legendary 787B Le Mans racer, using what was known colloquially as the “26B” motor. Since then, no other automaker has applied such a high-displacement, high-strung power unit because building a reliable example is near impossible.

Typically, a two-rotor design is the most ideal and optimal arrangement for usable everyday power. It should also be noted that engineering a four-rotor Wankel engine takes more than just conjoining two twin-rotor engines together at the eccentric shaft.

The challenge with adding more rotors is that it requires more engineering to make the engine work reliably before it begins to tear itself apart from instability. Such engineering means completely altering the firing order and redesigning the crankcase to withstand the different tolerances of the active combustion cycle.

Dahm has built a four-rotor engine in the past, which found its home in his all-wheel-drive RX-7 build. But never has he, or anyone, built one using Billet Rotor assemblies. Therefore, this is an exciting moment as this could be the world’s most durable 26B Wankel tribute and the first of its kind in North America.

Check out his progress below and expect to see the complete build at this year's SEMA show in Las Vegas.