The invention relates to a portion of a turbofan (1) extending about a longitudinal axis (A), comprising: —an outer wall (Pe) and an inner wall (Pi), defining a secondary duct portion (Vs), —a cascade of guide vanes (OGV), each guide vane extending within the secondary duct portion (Vs) between the outer wall (Pe) and the inner wall (Pi), wherein, in the region of the cascade of guide vanes (OGV), and in a plane orthogonal to the longitudinal axis (A), the distance from the outer wall (Pe) to the longitudinal axis (A) along a first axis (Xi) orthogonal to the longitudinal axis (A) is greater than the distance from the outer wall (Pi) to the longitudinal axis (A) along a second axis (X2) orthogonal to the longitudinal axis (A) and to the first axis (X1).