I used VHT on a stainless manifold on my 200sx, regularly was glowing orange (daily basis) and it was minted, still black after 6 months use.

tried it on my RST, it's still black but it's only been heated a few times

put it on an XR4x4 turbo's manifolds and it's started to come off as manifolds rusting, car sits around often though.

all 3 times i've heated the manifolds with a heat gun, it's always kinda powdery.