The compact engine, which Liquid Piston says is ready for series production, may not revolutionise the car industry, but it could be used in aviation for small unmanned drones and in stationary applications.
The gains come late for the Wankel motor, which has been around for nearly 100 years, but has failed to catch on in a big way.
Most recently Mazda fitted a small plug-in Wankel motor as a range extender in its electric MX-30 model.
Amid the march towards electrification, the revamped Wankel is one of several fresh ideas aimed at saving the ICE engine from extinction.
Others include the Atkinson engine, first produced in 1876, which provides variable stroke lengths and is still used mainly in gas-electric hybrids.
Liquid Piston said it has eliminated all the previous Wankel disadvantages such as seal bugbears and excessive fuel consumption.
The resulting XTS-210, two-stroke, supercharged, liquid-cooled rotary engine was developed as a "core engine" for the US Army. The engine is no larger than a basketball and produces a hefty 25 hp from a displacement of only 0.21 litres, says the company.
In the Mazda engines, a triangular piston rotates in a peanut-shaped housing, in the US version the piston is shaped like a peanut and rotates within three chambers.
