An engine is provided with a cavity so that a catalyst member can be contained within the engine when an engine head portion is attached to an engine block portion. This attachment of the engine head portion and engine block portion, which forms the engine structure, captivates the catalyst member within the cavity without the need for additional brackets and housing structures. The cavity is preferably located above or at the upper regions of first and second exhaust conduits which direct exhaust upwardly from the engine head portion toward the cavity and downwardly from the cavity within the engine block portion. The first and second exhaust conduits are preferably formed as integral structures within the engine head portion and engine block portion.