The temperature of exhaust gas discharged from a compact air-cooled engine used as a power source for an engine-driven working machine is reduced. An engine has a muffler mounted directly to the exhaust opening of the cylinder, and a resin muffler cover covering the muffler. An exhaust gas restriction member is provided to a wall surface of the muffler, and two exhaust passages serving as outlets for exhaust gas are formed in the exhaust gas restriction member. The exhaust passages are arranged independent of each other, and the streams of discharged exhaust gas are discharged to be slightly separated from each other as the streams flow away from the exhaust openings. The separated streams of discharged exhaust gas form a negative pressure space between the streams promoting the introduction of a cooling air stream into the negative pressure portion. Thus, the temperature of the exhaust gas can be reduced.

An aftertreatment module for the treatment of exhaust gasses from a power system includes a first aftertreatment brick and a second aftertreatment brick. The first and second aftertreatment bricks can be flow-through type catalysts for catalyzing byproducts in the exhaust gasses. The aftertreatment module can include a first channel directing the incoming exhaust gasses in a first direction through the first aftertreatment brick and a second channel directing the exhaust gasses through the second aftertreatment brick. The first and second channel can be in a side-by-side arrangement. To communicate the exhaust gasses between the first and second channels, a traverse channel can redirect the gas flow within the aftertreatment module.