An apparatus for diluting and diffusing engine exhaust, includes a diffuser pipe horizontally oriented and having an inlet connection to receive exhaust gases from an engine and having an outlet defined as an elongated opening on an upper surface thereof, the inlet being disposed at about a longitudinal midpoint of the diffuser pipe, a deflector mounted in the diffuser pipe opposite the inlet to divide an entering exhaust gas flow toward opposite ends of the diffuser pipe, a baffle formed as an elongated plate having a multiplicity of holes mounted in the pipe between the inlet connection and the outlet and extending a length of the diffuser pipe, and, a dispersing grate formed as an elongated plate having a multiplicity of holes and being mounted above the outlet and spaced therefrom, the dispersing grate having a curvature about a longitudinal axis, and being mounted with a convex surface facing the outlet.