Are you referring to the plastic engine cover or the actual bay?!
If it's just the actual plastic cover any red paint will do. Make sure to tape off the areas you don't want painted carefully. I lightly scuffed the plastic with an abrasive pad, then I wiped it down and sprayed a few coats of primer. I waited for that to dry, then sprayed a few coats of red. After that dried I sprayed a few coats of clear and called it good. I used all Duplicolor high heat paint on mine and it came out pretty legit.
IMG_0340 by
nickgdrums, on Flickr