A new compression release engine brake system has been developed which utilizes the well-known lost motion idea along with an entirely new valve resetting mechanism. The engine brake is fully integrated into the exhaust rocker arm, making it one of the most compact solutions on the market. The novel reset mechanism provides a pressure sensing reset timing which optimizes engine brake performance and valve train stress at all engine speeds. Hydraulic system simulation studies were performed to first verify the concept on paper. Once acceptable performance was predicted, physical prototypes were produced. The Cummins ISL 8.9L engine was chosen as a proof of concept platform due to its availability in the North American market and its factory engine brake option. The factory engine brake gives a data set for comparison while validating this new technology. All targets for engine brake function were achieved, and a substantial increase in performance was demonstrated.