A cast iron manifold will possibly suffer cracks due to repeated heat cycles affecting the microstructure and what is known as "growth of cast iron" then occurs.
Not much effect occurs below 400 degrees C but it increases as temperature rises above this.
With stainless steel manifolds it is not such a problem though, which is one reason why they are preferred for high output racing etc..(see the headers glowing in some Youtube videos!).
Keeping the heat IN the cast iron will enable the growth to be occurring so insulating a cast iron manifold is not really a long term method.
Ceramic coating does not have a huge insulation effect but does reduce radiant heat out into the engine bay thus of benefit.
Protecting sensitive components/areas is probably the best solution as it removes the insulation effect on the cast iron.
Hence the suggestion to insulate the air inlet system or even re-route it if practicable to both improve cold air intake and reduced heating of that air.
Perhaps a heat shield to shroud the manifolds(s) with ducted air to purge the air away would help?
DaveW's suggestion for insulating the cat will also have the benefit of getting it up to effective working temperature a bit quicker too.
It's a bit of a compromise between insulation and shielding to keep heat where it's of benefit and shield areas away from it if it's detrimental.
Each car/engine set up will require a bit of thought to achieve these two things.
For my Plus8 I have to consider shielding the manifolds and creating an airflow to purge the hot air, and getting a supply of cool air to the filter as possibilities as under bonnet area does get warm! If the filter box reaches 40 deg C in cool ambient temps then it's worth trying some simple shielding etc..
The car does not overheat though the fan does kick in when on stop and the heat builds near the fan switch.
In the end, how much actual effect on performance will this have? It won't be a huge amount with the standard cast manifold and exhaust.
If I was going into competition then its a route to consider seriously as every little increase will benefit cumulatively with other tweaks (engine mods/weight/mapping/aerodynamics etc.).



Plus Four MY23 Furka Rouge