Selecting the right injector for a CNG application involves considering the engine's capacity, which is specified as 400 to 500 CC. It's important to match the injector size and type to the specific requirements of the CNG system and engine performance. Factors such as fuel flow rate, pressure, and compatibility with the CNG fuel system should be evaluated. Additionally, consulting manufacturer specifications and expert recommendations can ensure optimal performance. Proper selection is crucial for efficiency and reliability in CNG applications.