An electric threat to Caltex, page-3

There are movements in other areas as well

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).
Gizmag

Such a small engine would be perfect for a hybrid, ie use the engine to run a generator so as to alleviate the battery problem