Process for the production of an intake manifold or an intake splitter comprising several pipes that are provided with regulating valves and whose end parts defining the outlet openings are preferably mutually aligned and grouped into at least one unit structure at the level of at least one attachment and connection plate, suitable for the mounting of said manifold or splitter on the cylinder head block of an internal combustion engine, whereby said or each plate defines a contact surface, preferably a contact plane, for a sealed assembly with said cylinder head block or a portion of the latter, this process consisting primarily in: - providing, on the one hand, a functional unit shaft /valves, and, on the other hand, parts to be inserted that form bearings, and, finally, a manifold body or splitter body having, at the level of the attachment and connection plate and end portions of the pipes, recesses and/or housings (8, 9, 9') for receiving the functional unit (5, 6) and above-mentioned parts to be inserted, the parts that form bearings being each composed of two mutually complementary branches, with front ends (7") and rear ends (7"'), whereby each branch has a recess that defines a portion of the rotational bearing; - mounting the parts that form bearings on the unit shaft /valves, more particularly on the shaft segments that extend between the valves, this mounting being performed by drawing together the two branches of said parts and by clamping the shaft segments that extend between two consecutive valves between the parts of bearings of the branches of each of said parts that are concerned; - installing the completed functional unit shaft /valves /parts that form bearings in the end portions and the recesses and/or housings for receiving (8, 9, 9'), by introducing said parts that form bearings in suitable housings that are formed or provided in the plate and located between the end portions of the pipes, whereby the front ends (7") of the branches of the parts that form bearings are located at the bottom of said housings; - implementing a molding or over-molding at the level of the surface of the plate that is intended to come into contact with the cylinder head block and that comprises the contact surface or contact plane, the material connected by molding or over-molding ensuring, on the one hand, the mechanical locking of the components of the completed functional unit (5, 6, 7) in their recesses and/or housings (2', 8, 9, 9') that respectively receive them and that constitute, on the other hand, formations (11, 14, 14') that work with or produce the sealing against gases between the end portions of the pipes and the cylinder head block, more particularly at the level of the contact surface or contact plane, as well as optionally between the pipes. - providing, on the one hand, a functional unit shaft /valves, and, on the other hand, parts to be inserted that form bearings, and, finally, a manifold body or splitter body having, at the level of the attachment and connection plate and end portions of the pipes, recesses and/or housings (8, 9, 9') for receiving the functional unit (5, 6) and above-mentioned parts to be inserted, the parts that form bearings being each composed of two mutually complementary branches, with front ends (7") and rear ends (7"'), whereby each branch has a recess that defines a portion of the rotational bearing; - mounting the parts that form bearings on the unit shaft /valves, more particularly on the shaft segments that extend between the valves, this mounting being performed by drawing together the two branches of said parts and by clamping the shaft segments that extend between two consecutive valves between the parts of bearings of the branches of each of said parts that are concerned; - installing the completed functional unit shaft /valves /parts that form bearings in the end portions and the recesses and/or housings for receiving (8, 9, 9'), by introducing said parts that form bearings in suitable housings that are formed or provided in the plate and located between the end portions of the pipes, whereby the front ends (7") of the branches of the parts that form bearings are located at the bottom of said housings; - implementing a molding or over-molding at the level of the surface of the plate that is intended to come into contact with the cylinder head block and that comprises the contact surface or contact plane, the material connected by molding or over-molding ensuring, on the one hand, the mechanical locking of the components of the completed functional unit (5, 6, 7) in their recesses and/or housings (2', 8, 9, 9') that respectively receive them and that constitute, on the other hand, formations (11, 14, 14') that work with or produce the sealing against gases between the end portions of the pipes and the cylinder head block, more particularly at the level of the contact surface or contact plane, as well as optionally between the pipes.