I saw a thread on another forum where a gentleman spoke about getting his headers ported by a professional porter. The porter showed videos of a header's CFM increase on a flow bench before and after his port job. From my understanding, the idea behind porting something is to maximize the CFM an inlet/outlet is able to "allow". If a header has excess slag from the welds, irregular port shape, lumpy bends, or a smaller than advertised collector, one could come to the conclusion that these "restrictions" could potentially be worked out, right? On the other hand, I saw an Engine Masters video where they put a bunch of dents in the headers up and down the primaries and lost nothing on the engine dyno. So this makes me think, was that porter onto something or was he backing a bogus service? Could a 1 5/8 short tube header flow as much CFM as a 1 3/4 short tuber header with a "port job"? Is there a possible CFM gain going from a 2in to 2.5in collector or is it marginal at that level? Just something to ponder over.