Abstract: An exhaust manifold includes: a double collecting pipe formed of inner and outer pipes; and an inner pipe retainer formed of a pair of semi-circular portions and a connecting portion. The inner pipe includes a collecting pipe portion and bifurcated branch pipe portions. The outer pipe covers outer peripheral portions of the collecting and branch pipe portions. The semi-circular portions are respectively connected to outer peripheral portions of branched branch pipe portions and an inner peripheral portion of the outer pipe. The connecting portion connects the semi-circular portions. The inner pipe retainer is interposed between the inner pipe and the outer pipe and is connected to the inner pipe and the outer pipe to define a certain gap therebetween. Exhaust gas from exhaust ports of a set of cylinders among a plurality of cylinders of an engine is introduced into the collecting pipe portion through the branch pipe portions.

Abstract: An exhaust manifold includes: a double collecting pipe having an inner pipe, including a collecting pipe portion and branch pipe portions, and an outer pipe, covering the collecting and branch pipe portions and thicker than the inner pipe; and an inner pipe retainer having semi-circular portions and a connecting portion, and thicker than the inner pipe and thinner than the outer pipe. The inner pipe retainer connects the inner and outer pipes with a gap therebetween. Exhaust gas from exhaust ports of a set of cylinders is introduced into the collecting pipe portion through the branch pipe portions. The total spot-welded area of the outer peripheral portions of the branch pipe portions and the inner peripheral portions of the semi-circular portions is larger than that of the inner peripheral portion of the outer pipe and the outer peripheral portions of the semi-circular portions.

Abstract: An exhaust manifold includes: a double collecting pipe formed of inner and outer pipes; and an inner pipe retainer formed of a pair of semi-circular portions and a connecting portion. The inner pipe includes a collecting pipe portion and bifurcated branch pipe portions. The outer pipe covers outer peripheral portions of the collecting and branch pipe portions. The semi-circular portions are respectively connected to outer peripheral portions of branched branch pipe portions and an inner peripheral portion of the outer pipe. The connecting portion connects the semi-circular portions. The inner pipe retainer is interposed between the inner pipe and the outer pipe and is connected to the inner pipe and the outer pipe to define a certain gap therebetween. Exhaust gas from exhaust ports of a set of cylinders among a plurality of cylinders of an engine is introduced into the collecting pipe portion through the branch pipe portions.

Abstract: An exhaust manifold includes: a double collecting pipe having an inner pipe, including a collecting pipe portion and branch pipe portions, and an outer pipe, covering the collecting and branch pipe portions and thicker than the inner pipe; and an inner pipe retainer having semi-circular portions and a connecting portion, and thicker than the inner pipe and thinner than the outer pipe. The inner pipe retainer connects the inner and outer pipes with a gap therebetween. Exhaust gas from exhaust ports of a set of cylinders is introduced into the collecting pipe portion through the branch pipe portions. The total spot-welded area of the outer peripheral portions of the branch pipe portions and the inner peripheral portions of the semi-circular portions is larger than that of the inner peripheral portion of the outer pipe and the outer peripheral portions of the semi-circular portions.