[ShelbyCSXT]

Muriatic acid can be found in most grocery stores in the pool section, and of course at any pool supply place. It's a pretty weak acid as i used to use the stuff to put in 2liter bottles along with some aluminum foil (homemade noisemakers, but please don't try making any). I spilled quite a bit of it on my hands, but i'm fine. Only a few times did it start to hurt, which some water took care of in a jiffy.

I dont know what concentration of it you should use, but if i was to guess, i'd say try full strength on some scraps you have laying around. If you happen to have any exhaust pipe scraps, it would have similar effects with the carbon build-up, etc..

Good luck and I hope it turns out well!!

P.s. Make sure your ceramic coating material is capable/designed for coating the inside of your headers. For example, I was going to get the Black Satin (BHK) to coat my manifold, turbo housing, etc. But it's not meant for inside use. Techline makes a different coating (MCS) that is designed for internal usage that will withstand 2000+ fahrenheit.