CNG has recently seen increased penetration within the automotive industry. Due to recent sanctions on diesel fuelled vehicles, manufactures have again shifted their attention to natural gas as a suitable alternative. Turbocharging of SI engines has seen widespread application due to its benefit in terms of engine downsizing and increasing engine performance .This paper discusses the methodology involved in development of a multi cylinder turbocharged natural gas engine from an existing diesel engine. Various parameters such as valve timing, intake volume, runner length, etc. were studied using 1D simulation tool GT power and based on their results an optimized configuration was selected and a proto engine was built. Electronic throttle body was used to give better transient performance and emission control. Turbocharger selection and its location plays a critical role. Turbocharger Wastegate actuator trials were conducted to select optimum actuator to restrict boost enough to meet power target. Various engine related MAP like main lambda, volumetric efficiency, MBT timing, Primary ignition timing, etc. were calibrated and saved in EMS. The full load curve was calibrated using EMS to meet performance target of 85 kW rated power and 285 Nm max torque. Further, through precise calibration of various ECU tables the engine managed to meet BS IV emission norms.