A turbocharger cartridge and engine cylinder head assembly, comprising: a turbocharger cartridge forming a unit that comprises at least a center housing rotating assembly, the center housing rotating assembly comprising a center housing defining a bore therethrough, bearings housed in the bore, a shaft rotatably supported in the bearings, a compressor wheel affixed to one end of the shaft, and a turbine wheel affixed to an opposite end of the shaft; an engine cylinder head and housing member formed together as an integral one-piece casting, the housing member defining a generally cylindrical receptacle in which the turbocharger cartridge is inserted in an axial direction, a radially outer surface of the center housing confronting a radially inner surface of the receptacle, wherein the turbocharger cartridge defines a cartridge oil circuit including an oil supply passage and an oil drain each defined in the center housing, the oil supply passage extending from the radially outer surface of the center housing generally radially inwardly to the bore; wherein the housing member defines an engine oil circuit including an oil supply conduit and an oil drain conduit, the oil drain conduit mating up with the oil drain in the center housing, the oil supply conduit connecting with a socket defined in the housing member, the socket extending from an outer surface of the engine cylinder head generally radially inwardly and mating up with the oil supply passage in the center housing; and an oil circuit connector plug removably installed in the socket, the plug defining a connector passage (160, 162) that mates up with the oil supply conduit in the engine cylinder head and with the oil supply passage in the center housing such that oil is conducted from the oil supply conduit through the connector passage to the bore; characterised in that the housing member further defining a compressor volute for receiving air pressurized by the compressor wheel and a turbine volute for receiving exhaust gas from an engine; a turbocharger cartridge forming a unit that comprises at least a center housing rotating assembly, the center housing rotating assembly comprising a center housing defining a bore therethrough, bearings housed in the bore, a shaft rotatably supported in the bearings, a compressor wheel affixed to one end of the shaft, and a turbine wheel affixed to an opposite end of the shaft; an engine cylinder head and housing member formed together as an integral one-piece casting, the housing member defining a generally cylindrical receptacle in which the turbocharger cartridge is inserted in an axial direction, a radially outer surface of the center housing confronting a radially inner surface of the receptacle, wherein the turbocharger cartridge defines a cartridge oil circuit including an oil supply passage and an oil drain each defined in the center housing, the oil supply passage extending from the radially outer surface of the center housing generally radially inwardly to the bore; wherein the housing member defines an engine oil circuit including an oil supply conduit and an oil drain conduit, the oil drain conduit mating up with the oil drain in the center housing, the oil supply conduit connecting with a socket defined in the housing member, the socket extending from an outer surface of the engine cylinder head generally radially inwardly and mating up with the oil supply passage in the center housing; and an oil circuit connector plug removably installed in the socket, the plug defining a connector passage (160, 162) that mates up with the oil supply conduit in the engine cylinder head and with the oil supply passage in the center housing such that oil is conducted from the oil supply conduit through the connector passage to the bore; characterised in that the housing member further defining a compressor volute for receiving air pressurized by the compressor wheel and a turbine volute for receiving exhaust gas from an engine;