The significant growth of the IC engine efficiency can be achieved among others by the diminishing of the charge exchange work and as well by arranging of the energy recovery in the engine system. The issue of the 6-stroke (3-revolution) cycle and its implementation in the entire IC piston engine cycle should be considered as an important proposal in this field of research. Increase of the energy efficiency occurs especially meaningful within the range of part load of IC engine. The internal energy of the combustion products from the first stage is trapped in the system and next effective used in the second added stage of the modified cycle. The characteristic element of the 6-stroke cycle is the liquid water injection into the charge captured in the engine cylinder, but the point of the water injection should be very attentively determined. (C) 2014 Elsevier Ltd. All rights reserved.