A customer sent us his Neon SRT-4 Injector cover that was painted, and due to underhood engine heat it bubbled and flaked off.
Lesson learned from this experiment: if you ever paint any underhood components of your engine bay, MAKE SURE They can tolerate the heat.
Powdercoat will usually last FAR longer and be much more durable than regular spray paint, so if you have access to a local powdercoater, then go that route!