Hello I would like to paint or coat my rusty exhaust manifolds . Has anyone tried some of the stuff in spray cans available at the parts store thanks in advance 

I have had very good results removing rust from cast iron exhaust manifolds ( any ferrous metal ) by using electrolysis. Google it. Pete

In regard to cleaning exhaust manifolds, what is the best way to get the baked on carbon deposits out of the inside of the manifold?

A youtube video of degreasing derusting a flathead engine using electrolysis. Check it out. Simple, safe( NO TOXIC RESIDUE) 

https://www.youtube.com/watch?v=njtyZzDBHzg
   Pete

Bama, I have used caustic old oven leaner in the past to soften the burnt on carbon. Did that long ago. No sure if the new "reformulated" cleaners works as good as the old. Do wear gloves. - Bob 

AKA   Bob-93021

Best way?  Sand blasting inside and out.  Removes rust, scale, carbon, slag and leaves a clean dry surface for paint.  Start out with high pressure, and lower the pressure for finishing to make the texture less rough.  I have ported several of them inside and left the inside with a polished surface.  Lots of work, but stealthy.  Joe-JDC

JDC