Painted Headers and rust
My stock manifolds are rusty as hella already so I don't really care if they look clean or not. I know even coated headers rust too after awhile
EVEN if it was rusted on the inside, either a hole has to be completely rusted through or the maybe the surface area had very bumpy textrure, maybe that could create turbulance.
The biggest thing to look out for are warped flanges, cracked or leaky tubing.
Coating process does take meterial out of the header and yes they do re-corrode over time.
Stainless for the win!!



