the central axis x of the inlet 6 the segment 11 has a substantially circular section the end segment 11 has a flared end 16 the concave portion of the flared end 16 is arranged on the side opposite the duct 2 the convex portion being turned toward the inside of said duct 2 as shown in fig2 the outer neck 7 is positioned bearing on the flared end 16 of the end segment 11 furthermore the end segment has a hole 23 situated between the outer neck 7 and the flange 3 furthermore the cannon 10 comprises a first segment 13 with a larger thickness toward the flange 3 extended by a second segment 14 having a smaller thickness toward the duct 2 the first segment 13 has substantially the same thickness as the flange 3 the second segment 14 has a thickness substantially corresponding to the thickness of the wall 9 the first and second segments 13 and 14 are connected to one another by a shoulder 15 the shoulder 15 delimits an annular surface substantially perpendicular to the longitudinal axis x of the inlet 6 in this way the outer neck 7 rests on the flared end 16 of the wall of the duct 2 with the flared end 16 in turn resting on the shoulder 15 of the flange 3 the method for manufacturing the exhaust volume described above will now be explained in reference to fig3 4 5 6 7 and 8 the method comprises the following steps deforming the outer neck piercing a hole in the end segment positioning the inlet of the exhaust duct across from the flange and securing the flange the end segment and the outer neck by adding a filler.