Abstract: A process and apparatus are provided to increase the retarding horsepower of a compression release engine retarder driven from the exhaust valve pushtube or the fuel injector pushtube. The mechanism includes a plenum communicating with the exhaust valve slave piston and the master piston driven by a remote exhaust valve pushtube or the fuel injector pushtube. A trigger check valve is located between the master piston and exhaust valve slave piston so that the initial motion of the master piston delivers energy to the plenum. At a predetermined point in the travel of the master piston, the trigger check valve is opened by the master piston to permit the delivery of the energy stored in the plenum to the slave piston. Additional pumping capability is provided by a second master piston while a control check valve communicating with the second master piston limits the intake of hydraulic fluid into the system after working pressures have been attained to that hydraulic fluid which may leak from the system.