Look at
this photo. You might also want to browse A.net for similar ones, which will help you.
From what I can see, you should add a rather well defined shade at the top of the intake (not as blurred as what you have done here) and use highlight to represent the lower part of the intake. Make sure your shading and lighting are coherent with the rest of your drawing.
Little guessing game: does anybody see something odd on that photo?