I always lightly sand my pipe, y-pipe, and
Can to remove some of the old paint,rust, and dirt. Then go to any auto parts store and get the best heat resistant header paint I can find somthing that says 1200-1500 degrees. Has always worked good for me. First ride out it will smoke so don't worry if you start smelling a weird smell. The y pipe still seems to get to hot for most heat resistant paint and will sometimes turn grayish.