Muffler Repainting

[Estecks]

So I have some really cruddy looking mufflers, they were sitting outside for a couple years. I tried to strip the paint with airplane stripper but nothing came off. So I tried to just paint them again with black high heat paint and it looks horrible. Is there anything I can do to get the mufflers down to a nice flat surface again so I can paint it nice or do I just need to deal with ugly ones from now on?