A large amount of torque is needed in moving heavy duty vehicle and machinery to achieve high acceleration speed or to perform activities at any off short time. This additional torque can be harness from hydraulic hybri hybrid has been considered as an alternative to fulfil the increased demands on higher efficiency and better systems, components and functionality of a vehicle. In this paper, a conceptual design of hydraulic hybrid test rig for engine proposed using a dynamometer test setup. A differential gear mechanism was identified as the vital component of the transmission system to couple both power generated from engine and hydraulic hybrid system. A large amount of torque is needed in moving heavy duty vehicle and machinery to achieve high acceleration speed or to perform activities at any off-road condition or rough terrain in a short time. This additional torque can be harness from hydraulic hybrid system. Hydraulic hybrid has been considered as an alternative to fulfil the increased demands on higher efficiency and better systems, components and functionality of a vehicle. In this paper, a conceptual design of hydraulic hybrid test rig for engine performance enhancement was proposed using a dynamometer test setup. A differential gear mechanism was identified as the vital component of the transmission system to couple both power generated from engine and power coupler; diesel engine; accumulator; hydraulic motor A large amount of torque is needed in moving heavy duty vehicle and machinery to achieve road condition or rough terrain in a d system. Hydraulic hybrid has been considered as an alternative to fulfil the increased demands on higher efficiency and better systems, components and functionality of a vehicle. In this paper, a performance enhancement was proposed using a dynamometer test setup. A differential gear mechanism was identified as the vital component of the transmission system to couple both power generated from engine and hydraulic motor.