A spark ignited internal combustion engine comprising a plurality of cylinders, the engine including, for each cylinder: a combustion chamber within the cylinder head, said chamber being spaced from its respective cylinder; a transfer orifice providing communication between the respective cylinder and the combustion chamber; a fuel injector arranged to deliver, in use, liquid fuel spray into the chamber; a spark igniter located within the combustion chamber; the engine including: a cylinder head to close each and all of the cylinders at one end; an exhaust valve for each cylinder located in the cylinder head, leading to an exhaust duct or exhaust manifold; a piston located in each cylinder for reciprocating movements therein; characterised in that: at least one cylinder being made, in use, to operate on a two stroke cycle and at least one cylinder being made to operate on a four stroke cycle; the engine defining one or more air inlet ports for the or each of the two stroke cylinders, which permit air inflow into the cylinders when the respective piston reaches the end of its expansion stroke; the engine including: an air inlet valve for the or each of the four stroke cylinders situated in the cylinder head and communicating with such cylinders; a device to activate all valves situated in the cylinder heads of all cylinders such as a cam shaft or a rotary valve; a turbocharger including a compressor impeller which communicates with the air inlet ports of the two stroke cylinders and a turbine which communicates with the exhaust valve(s) of the four stroke cylinder(s); wherein at least one cylinder of the engine which operates on the four stroke cycle supplies exhaust gas to the turbocharger turbine impeller whose compressor impeller supplies air to the air inlet ports of the or each of the two stroke cylinders. a combustion chamber within the cylinder head, said chamber being spaced from its respective cylinder; a transfer orifice providing communication between the respective cylinder and the combustion chamber; a fuel injector arranged to deliver, in use, liquid fuel spray into the chamber; a spark igniter located within the combustion chamber; a cylinder head to close each and all of the cylinders at one end; an exhaust valve for each cylinder located in the cylinder head, leading to an exhaust duct or exhaust manifold; a piston located in each cylinder for reciprocating movements therein; at least one cylinder being made, in use, to operate on a two stroke cycle and at least one cylinder being made to operate on a four stroke cycle; the engine defining one or more air inlet ports for the or each of the two stroke cylinders, which permit air inflow into the cylinders when the respective piston reaches the end of its expansion stroke; the engine including: an air inlet valve for the or each of the four stroke cylinders situated in the cylinder head and communicating with such cylinders; a device to activate all valves situated in the cylinder heads of all cylinders such as a cam shaft or a rotary valve; a turbocharger including a compressor impeller which communicates with the air inlet ports of the two stroke cylinders and a turbine which communicates with the exhaust valve(s) of the four stroke cylinder(s); an air inlet valve for the or each of the four stroke cylinders situated in the cylinder head and communicating with such cylinders; a device to activate all valves situated in the cylinder heads of all cylinders such as a cam shaft or a rotary valve; a turbocharger including a compressor impeller which communicates with the air inlet ports of the two stroke cylinders and a turbine which communicates with the exhaust valve(s) of the four stroke cylinder(s); wherein at least one cylinder of the engine which operates on the four stroke cycle supplies exhaust gas to the turbocharger turbine impeller whose compressor impeller supplies air to the air inlet ports of the or each of the two stroke cylinders.