[.:4:.]

Consider this, paint them black with high temp paint. Reason being, black may absorb more radiant heat, however if its hotter then the ambient air it will dissapate heat faster then bare steel or silver. It kind of explains why black cars sitting in the sun get hotter when you jump into them as opposed to a white one, and why a lot of high temp items in race cars etc are black. A heat sheald is effectively a a heat sink. With enough air flow it will remove heat into the air, but without air flow, once it heats up to the temp of the heat source it will be of no help. Dunno how much air flows through the engine bay but its something to scratch your noggin.