PURPOSE: To obtain a light weight and thin wall exhaust manifold, improve fuel consumption, and advance timing to activate a purifying catalyst, by forming a plurality of exhaust passages and meeting parts separated into gutter-like form curved in three dimensional direction and having semicircular sections out of sheet metal, constituting composite exhaust pipes through welding the front side and the back side semi-bodies, and welding flanges on both ends.
CONSTITUTION: Front semi-bodies 2a, 3a and back semi-bodies 2b, 3b constituting respective composite exhaust pipes 2,3 are press-worked out of heat resisting metal plates, formed into semicircular gutter-shape along the full length of exhaust passages 8, 9, 11 and on the terminal ends of meeting parts 10, 13, and recessed parts of two rows are nearly formed into V-shape on the upper stream side of the meeting parts 10, 13. Respective semi-bodies are curvedly formed in side direction of the arrow mark 15 and in depth direction of the arrow mark 16, respective side ends 17, 18 are also curved, the side ends are overlap-joined, and fixed by welding 2c, 3c. The pipe 2 is largely curved in depth direction, extended crossing over the exhaust passage 11 of the pipe 3, and the all exhaust passages are largely curved in proximity to an inlet flange 4. Inlet and outlet flanges 4, 5 are welded on both ends of the pipes 2, 3.