Hello again. I was thinking of adding a header to my 2.5. I know the current manifold is cracked I hear it and can see a blue grey color above the mounting flange. I was wondering about how much of a power gain is it. I also believe work was done on it before because it looks as if the back bolt is missing or snapped off. If there is a back bolt missing should I remove the head and drill it out, or better yet would it be better to have the head rebuilt and ported? I do fear doing the work althoe I did replace an exhaust manifold on a 94 without any issues. Thanks again.