The BMI 650 marine diesel engine is upgraded in Iran and its use is changed and is now suitable to be used in marine vessels with maximum power of 650 horse power. The improved items in the engine include compression ratio change, heat exchanger design, ECU, etc. Having constant torque in different operational speed of the engine, it could be used with optimal performance in the Persian Gulf climate. The engine can be used for different applications including medium duty usage for patrol, passenger and cargo vessels