I've had thermal wrap on pipes and turbo dumps and have the dump/down pipe coated on my TD5 D2.
First up, you'll need a dyno to measure any HP/torque gains, the bum dyno won't notice it. In another lifetime I've had sensitive race drivers not able to pick a 4% power increase, although they could pick a change in the torque curve.
In theory, the slight increase in gas velocity will help but it's not a noticeable change like changing a cam.
Use a reputable company or try and view work that's at least 12 months old.
When I bought the 3" system for the Disco I had the option of having the dump 'ceramic coated' by the system manufacturer.
This was cheaper and easier then me sending the dump off to my coater
The system is 409 stainless, so will stain or rust blemish in use..
I have rust bleeding through the coating all along the dump and the system is only a couple of years old.
The manifold was done at the same time by another company (of my choice) and it still looks as new.
The big advantage for me is reducing under bonnet temps, but it has to be thick enough to make a difference.
You've probably already discounted header wrap when you're asking about coating, but I will say IME wrapped mild steel pipes rust out far too quickly, even when aluminised. I've had to repair too many headers and dump pipes that were wrapped.
Hope that helps
Bookmarks