26326402 A description various inventions related to internal combustion engines are disclosed in copending application ser nos 09 150 315 and 10 021 192 both of which are incorporated herein in their entirety by reference the basic design of barrel engines may be best understood by reference to these disclosures the present disclosure discusses only portions of a barrel engine design those of skill in the art will understand how these portions interact with the remainder of a functional engine the present invention provides for a method of creating boost air for the combustion process of a single ended style of barrel engine in order to improve its overall power density this is done by extending the piston assembly such that an air compressor piston head is included opposite of the power piston head giving an appearance similar to conventional barrel engine double ended pistons a schematic of the configuration is illustrated in fig1 referring to fig1 a reciprocating piston assembly 1 is assembled within two co axial cylinder bores a power cylinder 2 and an air compression cylinder 3 the piston assembly includes a combustion piston 20 in the power cylinder 2 and an air compression piston 21 in the air compression cylinder 3 the pistons are interconnected by a connecting rod 22 with the pistons connected to opposite ends of the connecting rod 22 the pistons 20 and 21 and the connecting rod 22 may be formed as a single piece or may be formed of multiple pieces the piston assembly 1 is connected to a rotating track or cam.