Rep Power: 268

So I finally replaced my stock header with a used DC Sports header that's been sitting in my office for forever. When I took off the stock I thought I'd take some pics to compare.

When looking at the inlets to the stock header there is a built up ring in each inlet. In the picture the stock is on the right. Follow the silvery mating surface to the inlet and you can see a drop into the inlet then the built up ring I am talking about then it goes back to the interior of the piping.

Is this a carbon build up, attachment weld of the piping to the mating surface, or some other build up that is supposed to be there? It would make sense if it was a carbon build up only if the holes of the gasket were smaller than the ports out of the head since there would be turbulence around the protrusion and particles would be deposited in the inlet. I just want to know if this is common construction for all stock headers, a strange build up only on my stock header, or whatever? I haven't tried to "clean" it off yet, but I'll probably try if it's not normal.

 
Rep Power: 0

They are welds. If you grind them down a little, it helps flow.