Now the company is back with the 70 cc X Mini engine, which LiquidPiston's President and Co-Founder, Dr Alexander Shkolnik unveiled on Wednesday at the SAE International/JSAE 2014 Small Engine Technology Conference in Pisa, Italy.

In a telephone interview with Gizmag, Shkolnik tells us that the decision to concentrate on smaller engines was based on public feedback and that over the past two years, LiquidPiston has been improving this technology. He says that the power-dense rotary four-stroke engine prototype's basic architecture is pretty much the same as that of the X2, which shows the scalability of the engines.

The X Mini has a 4 lb (1.8 kg) core, is 30 percent smaller and lighter than a comparable engine, fits in a 6.6 in x 6.2 in x 5.4 in (16.7 x 15.7 x 13.7 cm) box, and has only two moving parts. According to Shkolnik, the X Mini is spark ignited because it suits a petrol engine of this size better than compression ignition used in the X2. Despite its size, the X Mini puts out 3.5 bhp and when fully developed could punch 5 bhp with a weight of only 3 lb (1.3 kg).