Dimpling/clearancing the header tubes in the upper area of the runners right outside the head ports where the most exhaust flow occurs, to accomodate what looks like a water pipe ...
My bad, I blew the pic up and it looks like the dimpling could be as a sort of divider between where the 2 exhaust valves flow enters the port, provided this is,as I expect, a 4 valve head. Still can't say this would be my choice for the best flow.
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