Aluminizing is done primarily in applications (like exhaust) where a steel part exceeds the temperature limits of other coatings and platings. It is done by feeding an Aluminum wire into an Acetylene flame where it melts and sprays onto the steel part where it solidifies due to the high thermal conductivity of Aluminum. It is an anti-corrosion coating.

Because Aluminum is such a good conductor of heat, the steel should run cooler because the coating is sucking heat out and rejecting it to the air surrounding it- the opposite of a thermal barrier coating. It works great on an old Ferrari F1 car where the bundle of snakes exhaust is just hanging out there in the airflow, a situation not too dissimilar to a 911.

the inside is where you really want the ceramic coating

the exhaust ports are where you really want it

Except you must be careful if you have a turbo. 964 ceramic exhaust port liners often crack. If that head is used on a turbo and the crack happens, you need a new turbocharger. And it is not cheap to have them repaired- easier to change to non-coated heads.

The coating will keep the exhaust gas more energized but if the coating is too brittle and flakes off it can ruin the turbo.