A few tips, I've painted three intakes and two sets of valve covers over the years with good results.
-If you can at all afford it, get them sandblasted. Much less time consuming, and you'll have a better surface to work with.
-If you can't find an affordable sandblasting outfit, or don't want to sandblast them, sanding will still give OK results. Make sure you degrease the **** out of them first. I've had good results with Castrol Super Clean (or something like that, it's in a purple bottle). I use those cheap horsehair paint/chip brushes to scrub with, and rinse well. After that is done, you're going to want to use some sort of solvent to make sure the finer oils are gone. Brake cleaner may be too harsh and take the original paint off, making for a total mess to try and sand. I would stick with something like denatured alcohol.
-If sanding, you won't need to get everything down to the bare metal. Just scuff it enough for the new paint to have a good base to adhere to. In fact, you might find that using some rougher grit scotchbrite pads will be a lot easier. They conform to the irregularities of the surface better. You won't need to use etching primer if you're not going down to the bare metal. Any old primer will do in this case. Shoot a couple good coats of primer, and then you can start your color coats.
-I used Duplicolor wheel paint in the charcoal color on my valve covers 3 years and 60k miles ago, and it still looks like the day I did it. I used their wheel clearcoat over the charcoal as well. If you use this stuff, make sure you follow the timelines given on the directions on the can. If you wait too long/not long enough to spray the clear it will wrinkle the color coat. I used some fine scotchbrite in between coats for a nice smooth surface.
-On my intake I used Duplicolor metallic paints, with their regular crystal clear coat spray. This intake has only been on for about a month, but it's been through quite a few heat cycles and still looks great. Again, scotchbrite between coats made for a nice finsished surface.
The important thing to remember is prep. The more time you take to prep correctly, the better your results will be. Also, any paint will chip if hit hard enough. If you're painting these parts, you have to expect chips at some point, and know you'll have to fix them. I scratched the **** out of my intake putting it back together, but touched it up with a small brush and you can't even tell it happened. Powdercoat will also chip, if hit hard enough.
Good luck with the project!
