Air supply unit for an internal combustion engine

An air supply unit (1) for an internal combustion engine; the air supply unit (1) is provided a number of butterfly valves (3) and a distributor device (6), the latter being provided, for each butterfly valve (3), with a distribution duct (10) capable of placing an internal duct (4) of said butterfly valve (3) in communication with a chamber (7) of the distributor device (6) connected to an intake box (2) by means of a first air duct (8) regulated by a solenoid valve (9); inside the distributor device (6), each distribution duct (10) is connected to the intake box (2) by means of a corresponding second air duct (11) regulated by a respective bypass screw (12) and is connected to a corresponding regulation duct (13) opening into an air intake (14), which is accessible from the outside of the distributor device (6) and is normally closed by an associated removable plug (15).