How the elusive 4-rotor rotary engine works


As the old saying goes, there is no replacement for displacement. That's not the case when it comes to rotary engines, which typically have very small displacement. Instead of cubes, if you want a rotary to make more power you do two things: add more rotors and/or slap on a turbocharger or two.

Noted rotary aficionado Rob Dahm did both with his 1990s Mazda RX-7. He put together an engine with four rotors--something never done in a production car--and a big, honkin' turbo. Dahm showed the car a few weeks ago at the annual SEMA show, and Jason Fenske of Engineering Explained was on hand to check it out. The build got Fenske's inquisitive mind thinking about how those rotors spin in relation to one another.

CHECK OUT: Four reasons why the rotary engine is currently dead

The Mazda RX-7s and RX-8s we all know and love have two rotors. A few race cars have used three, and some individuals have built monster motors with four, six, and even 12 rotors.

When a 2-rotor engine runs, the rotors are spin in a 180-degree relation to one another. A 3-rotor engine places the rotors 120 degrees apart. And the 4-rotor? On the eccentric shaft, rotors 1 and 2 sit at a 180-degree angle to each other, and so do rotors 3 and 4, though 3 and 4 are rotated 90 degrees from rotors 1 and 2. The firing order is 1-3-2-4, and that means each rotor spins at a 90-degree relation to those before and after it.

There is a good reason for this and our host is here to make sense of it all. He even gives a basic primer on how rotary engines work. Watch the video above to see Jason break down complex engineering concepts, even for those of us who have never turned a wrench.

 
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