Ive been looking into making a valve cover or skinning a valve cover as well making an exhaust tip. Can this be done with Carbon fiber? Im assuming the Fiber itself can handle the heat but

Potentially but you would be likely to find that the surface of the resin would deform slightly as the post-cure imparts energy into the part and any uncured resin (on a molecular scale) will move around and chain link with their respective hardener molecules. This often causes the resin to sag on the surface when done out of the respective mould tool and so at the end, you could find that you need to polish the part to bring it back to a smooth, flat finish.