Abstract: A method and apparatus for controlling the intake manifold air pressure during compression release engine retarding of a turbocharged internal combustion engine are disclosed. The apparatus comprises a solenoid actuated pressure responsive means communicating with the intake manifold and electrically connected to the control circuit for the compression release retarder. In one form of the invention, intake manifold air pressure is controlled so as not to exceed a predetermined maximum pressure during compression release retarding while in another form of the invention the intake manifold air pressure may be adjusted by the operator to any level up to a predetermined maximum level. By controlling the intake manifold air pressure the magnitude of the retarding horsepower developed by the engine and the loads imposed on certain of the engine components may be controlled.