The invention relates to a dilution and dispersion device for the exhaust and/or cooling gases of a vehicle's engine, that incorporates blades and a hub. The hub of said device incorporates means intended to reduce the loss in the gaseous flow rate generated by said gases. The flow rate loss reduction means are constituted by one or several openings in said hub or by a profiled element allowing said gases to be defected towards said blades. The blades are fastened to a ring.