116 includes the catalyst retainer rack 128 that rides on the rack slide 129 a gasket 130 for the catalyst rack 128 and a shoulder 126 located within the catalyst chamber 136 for seating the gasket 130 any suitable means for seating the catalyst rack 128 against the shoulder 126 with the gasket 130 between them can be used for example a cam device not shown an access door 118 is used to access the catalyst rack 128 for removing or installing the catalyst elements 124 a top view of the catalyst retainer rack 128 with two catalyst elements 124 is shown in fig5 referring again to fig3 the exhaust from the engine enters the first volume chamber 134 through exhaust inlet 110 the number of exhaust inlets 110 depends on the number of cylinders in the engine typically one for each cylinder or a pair of cylinders a relief valve 114 is generally positioned opposite the exhaust inlet 110 due to the baffle 102 and changing the direction of flow of the exhaust within the first volume chamber 134 liquid and solid particulates are at least partially removed from the exhaust these collect in the lower silencer head 132 a drain line and valve assembly 112 is attached to the bottom of the lower silencer head 132 to allow removal of any accumulated liquid and particulate solids the volume of the first volume chamber 134 is sufficient to dampen spurious pressure excursions or pulsations to avoid damage to the catalyst elements 124 the exhaust then exits the first volume chamber 134 through flow pipes 106 into the second volume chamber 136 the leading face of the catalyst elements 124 are spaced from the exit of the flow pipes 106 to allow.