Abstract: A compact cylindrical-form or ball-shaped exhaust gas converter is provided with a hemispherical-form inlet end housing section to provide a gas expansion space around a perforated interior partition which, in turn, is maintained a spaced distance from such housing section to extend from the gas inlet port to a zone adjacent the upstream end of the centrally positioned catalyst retaining section. This special gas inlet construction serves as a gas pressure amplitude modulator to average or dampen pulsations in the exhaust gas stream from an internal combustion engine so as to substantially eliminate damage to the catalyst being maintained in the converter.