Abstract: An exhaust brake and method of operating an exhaust brake are disclosed. The exhaust brake may have a housing having a central opening and a boss with a central bore, wherein the central bore intersects the central opening. A butterfly gate may be pivotally mounted in the central opening. The butterfly gate may have a bypass opening provided in an outer edge of the butterfly gate, and an upstream side. A dual-diameter piston may be slide-ably disposed in the central bore. The piston may have a lower end received in the bypass opening and an upper end distal from the bypass opening. One or more passages may extend between the central opening and the central bore at the upstream side of the butterfly gate, and a spring may bias the piston lower end into the bypass opening. The piston lower end may selectively unblock the bypass opening responsive to the application of static exhaust gas pressure to the piston upper end.