I assume,..... their ceramic coated ?
If so, not much if most of it has burnt off. It also depends on the quality of ceramic, the painters skills of laying it down, the tumbler and hand polishing.
I had mine re-coated from this business. They are beautiful and Speedway Motors in Lincoln Ne. has these guys do most of their work on headers ect.
Tell them Kevin with the blue cobra sent you. They love Cobras.
http://www.moorepower.com/