Diesel engines modified to be fueled with gaseous fuels experience problems with knocking and pre-ignition, limiting the compression ratio and efficiency of the engine. A new combustion chamber for a gaseous fueled internal combustion engine, in which the combustion chamber is defined by a cylinder head, a bore in a cylinder block and a piston reciprocating in the bore, comprises a piston portion of the combustion chamber defined by a recessed shape in a piston crown; and a head portion of the combustion chamber defined by a recessed surface in the cylinder head. A ratio between the piston portion of combustion chamber volume and the head portion of combustion chamber volume is in a range of 0.7 to 1.3.