Although there's no numbers yet, they do have a working prototype installed on kart.
http://liquidpiston.com/
Looks promising. I'm hoping to see this one day at Le MansThe engine achieved highest power per unit of weight
This is the major advantage of this engine because physics defines how well an engine's going to work,. And, according to our calculations — it has been published and checked and rechecked a number of times — if the thermodynamic cycle holds true, then the engine will be the most efficient engine.
It's a fundamentally different thermodynamic cycle, architecture and operation; a compression-ignition HEHC (high-efficiency hybrid cycle. An improved thermodynamic cycle that helps enable max fuel efficiency. The engine's two basic moving parts, the shaft and the rotor, allow it to come in a compact size and operate with little vibration or noise, the company says.