When Optimum's Coatings first came to market, they were advertised as pre-polymer resins that formed a bond with/to Clear Coat paints (BC/CC).
Much discussion was held on their use on Single Stage paint, with Dr. G himself once again saying that the OC-Coatings were formulated for use on BC/CC paint systems.
Then...Seemingly, to me, out of the blue: It was being said that the OC-Coatings were now to be considered compatible...being able to bond, as it were...with varying metal surfaces: Chrome-wheels/exhaust (decorative), Stainless Steel-exhaust/trim, etc.
I'm no Materials Scientist, but this bonding cross-over ability of Coatings from one type of material to another...especially metals...(with, IMO, the passivation process of certain metals even being brushed aside) is the source of my only complaint with Coatings in general, OC-Coatings in particular.
Therefore:
Applying Coatings to exhaust system components is something I won't do. My money is better spent elsewhere.
JMO...Of course: YMMV.
Bob