Back in the 1970s, Wankel engines were the future. Lots of companies—Mazda, Mercedes-Benz, and GM among them—invested in rotary research, and even Rolls-Royce got in on the fun. Yes, the world's most luxurious automaker once developed a Wankel—a four-rotor, diesel-powered unit designed for military use.

Jason Fenske of Engineering Explained made a video on this unusual engine after seeing a Jalopnik article about it, going into what made this Wankel work. Rolls-Royce was attracted to the Wankel for its compact dimensions, but wanted to pursue a diesel-powered version for fuel efficiency. Unfortunately, it's tough to build a rotary with the high compression necessary for diesel.



Rolls-Royce had an interesting solution. The design uses a large rotor to feed unburned air-fuel mix into a smaller rotor, effectively using the twin-rotor engine to supercharge itself. The 3250-cc larger rotor multiplied the smaller 1265-cc rotor's compression ratio 2.57 times.

The result was 350 hp, comparable to a contemporary V8 diesel, in a much smaller, lighter package. Jalopnik reports that at least four prototypes were built, though the project was killed not long after.

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