The one thing I noticed about engine enamel a few years ago, was that if you spilled gasoline on it, it would wash off! I assumed that engine enamel, like high temperature manifold paint, needed to be heat cured. I have found that regular Rustoleum gloss black rattle can paint gives me the highest gloss, but I re-paint within 30 minutes to an hour without sanding between coats. Doesn't craze if you re-paint within the hour.
For aluminum, I usually bead blast and then use Duplicolor aluminum wheel paint, with or without primer, but it is still not very resistant to chipping. Is there a primer that really works with aluminum?
Tom