well i can shed some light for ya on exaust manny paint. Ive been showing my challenger for 12+ years and it seems about every year or two they gotta get redone. Ive tried everything from the eastwood paint, vht rattle can, por, no name, ect.......and all ive found is it really dosent matter. The eastwood paint in a can that you brush on does a great job but can get messy since it wont fully cure till you bake the finish or install them and fire up the car. Vht and other rattle cans also do a decent job its just the coats are thinner so you wont have as long of a paint life. It's just something ive learned to live with. Preping the surface is a "must do" personally i like soda blasting cause it wont harm the metal casting pours ect.......it just can get a lil messy but whip up the cleaning solution and bingo your ready. Colors dont seem to matter the darker gray will last a lil longer but i like the eyes candy of the brighter alum./silver. Good luck!
