Yep, that's why you want it done by a reputable company. This comes from my cousin who is a certified welder, he says only doing the outside will actually weaken the metal and welds.

 

It's generally not a good idea to coat the inside of a manifold, even if you build the thing from scratch with the inner surface prepped properly for coating before welding it up, the scouring action and pressure from the exhaust waves can still make it flake off (That's straight from a guy who develops and applies the coatings on half a dozen F1 cars, although unfortunately he's not a certified welder...he does have a materials and tribology doctorate though if that counts...)

 

If money isn't a object I would do ATP Inconel wrap. I got the head shield for my turbo and you can touch it after you run the car hard and not burn yourself.

 

THIS THIS THIS THIS

Swaintech is local to me and is the ONLY true ceramic coating offered in the industry. Everyone else is just a copy cat.