An exhaust device of a six-cylinder engine includes first to sixth cylinders and a manifold extending from the first to sixth cylinders. The back pressure valve comprises a cylindrical body comprising a venting port coaxial with a longitudinal axis of the cylindrical body and a plunger disposed in the venting port, wherein the plunger comprises a stem that extends from the venting port into an adjacent cavity of the cylindrical body. A conductive layer is applied on the sheath and the spherical elements arranged thereon, said conductive layer having a resistivity.