Video: LiquidPiston’s 70cc Rotary Engine Spins to 10,000 RPM


Yes, what you’re looking at is a real rotary engine that is just a little bit bigger than an iPhone. This innovative little 4-stroke motor can produce 5 horsepower at 10,000 rpm and do so with only two moving parts. Officially unveiled by LiquidPiston during November’s SAE International/JSAE 2014 Small Engine Technology Conference in Italy, the “X Mini” is the successor to the company’s initial four-pound prototype that expelled 3.5 horsepower at 10,000 rpm.

Unlike its predecessor, Liquid Piston says that once finalized, X Mini could spin 15,000 rpm making more than five horsepower while weighing only three pounds. “The X Mini is an incredible breakthrough, and we expect to further optimize the engine for increased power (greater than 5 horsepower) and efficiency, and even lower operational noise,” says Dr. Alexander Shkolnik, president and co-founder of LiquidPiston.

Shkolnik sites LiquidPiston’s patented thermodynamic cycle and engine architecture as its greatest asset. Although previous larger displacement engines from the company produced 40 and 70 horsepower, the X Mini employs a High Efficiency Hybrid Cycle (HEHC) that allows the engine to be equally effective as it is condense, making it ideal for small displacement markets like “lawn and garden equipment, small motorcycles, robotics, range extenders for hybrids, auxiliary power units and even unmanned aerial vehicles,” according to a report by EngineLabs.

It continues, “The HEHC technology is said to optimize fuel efficiency by combining the best features of four current automotive engine cycles: high compression ratio in diesel; constant volume combustion in Otto; over-expansion to atmospheric pressure in Atkinson; and internal cooling with air or water in Rankine.”

Although similar to a Wankel or rotary engine with three separate combustion chambers to create three power strokes per revolution, LiquidPiston stresses that the engine doesn’t operate identical to the aforementioned engines. A closer study of the video below shows how the design is distinguished from other rotaries. Of course, the X Mini doesn’t offer itself for major applications in the PWC market, but a larger 70-horsepower unit using the same advanced technology could prove very useful for aftermarket standup ski builders.

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Kevin Shaw

Kevin Shaw

Editor-in-Chief – Kevin Shaw is a decade-long powersports and automotive journalist whose love for things that go too fast has led him to launching The Watercraft Journal. Almost always found with stained hands and dirt under his fingernails, Kevin has an eye for the technical while keeping a eye out for beautiful photography and a great story.

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