A catalytic converter apparatus comprising: a catalytic converter; a flow path for directing exhaust gas through the catalytic converter; a cavity for housing the catalytic converter; and a cooling apparatus for cooling at least a part of an inner surface of the cavity; wherein when the catalytic converter is housed within the cavity a gap is formed between the inner surface of the cavity and an outer surface of the catalytic converter with the gap extending around a major portion of the outer surface of the catalytic converter; characterised in that: the catalytic converter is supported at one end by a releasable coupling comprising bolts and extends from this end into the cavity, being thereby releasably held within the cavity; and in that the releasable coupling further comprises a seal including a flat sealing ring between two flanges (42, 44, 46); wherein the apparatus comprises an exhaust inlet and either: a) the catalytic converter is integrated with the exhaust inlet, and the sealing ring is placed between a flange of the integrated catalytic converter and exhaust inlet assembly and a flange of the cooling jacket; or b) the catalytic converter is separate from the exhaust inlet, the exhaust inlet, catalytic converter and cooling apparatus are joined together with two sealing rings wherein each of the exhaust inlet, catalytic converter and cooling apparatus is provided with a flange (42, 44, 46), and the three flanges are joined together with the sealing rings between each set of flanges. a catalytic converter; a flow path for directing exhaust gas through the catalytic converter; a cavity for housing the catalytic converter; and a cooling apparatus for cooling at least a part of an inner surface of the cavity; wherein when the catalytic converter is housed within the cavity a gap is formed between the inner surface of the cavity and an outer surface of the catalytic converter with the gap extending around a major portion of the outer surface of the catalytic converter; characterised in that: the catalytic converter is supported at one end by a releasable coupling comprising bolts and extends from this end into the cavity, being thereby releasably held within the cavity; and in that the releasable coupling further comprises a seal including a flat sealing ring between two flanges (42, 44, 46); wherein the apparatus comprises an exhaust inlet and either: a) the catalytic converter is integrated with the exhaust inlet, and the sealing ring is placed between a flange of the integrated catalytic converter and exhaust inlet assembly and a flange of the cooling jacket; or b) the catalytic converter is separate from the exhaust inlet, the exhaust inlet, catalytic converter and cooling apparatus are joined together with two sealing rings wherein each of the exhaust inlet, catalytic converter and cooling apparatus is provided with a flange (42, 44, 46), and the three flanges are joined together with the sealing rings between each set of flanges. the catalytic converter is supported at one end by a releasable coupling comprising bolts and extends from this end into the cavity, being thereby releasably held within the cavity; and in that the releasable coupling further comprises a seal including a flat sealing ring between two flanges (42, 44, 46); wherein the apparatus comprises an exhaust inlet and either: a) the catalytic converter is integrated with the exhaust inlet, and the sealing ring is placed between a flange of the integrated catalytic converter and exhaust inlet assembly and a flange of the cooling jacket; or b) the catalytic converter is separate from the exhaust inlet, the exhaust inlet, catalytic converter and cooling apparatus are joined together with two sealing rings wherein each of the exhaust inlet, catalytic converter and cooling apparatus is provided with a flange (42, 44, 46), and the three flanges are joined together with the sealing rings between each set of flanges. a) the catalytic converter is integrated with the exhaust inlet, and the sealing ring is placed between a flange of the integrated catalytic converter and exhaust inlet assembly and a flange of the cooling jacket; or b) the catalytic converter is separate from the exhaust inlet, the exhaust inlet, catalytic converter and cooling apparatus are joined together with two sealing rings wherein each of the exhaust inlet, catalytic converter and cooling apparatus is provided with a flange (42, 44, 46), and the three flanges are joined together with the sealing rings between each set of flanges.