[Jeff Lee]

I had some custom headers built by REF who is recognized as a pretty good builder. Based on my dyno inputs, he selected a merge collector with a big venturi and big outlet. Car felt lazy but it was pretty close in ET to the headers I had previously (Headers by Ed).
I called REF and of course he said my engine didn't make the power I claimed and he sent me a smaller venturi, smaller outlet. It immediately had a fuel starvation problem off the line (bowl running empty) but still had the best 60' ever. I installed a larger needle and seat which I had been wanting to try (but never seemed to have a problem) and immediately picked up .200 over my previous best ET with the best incremental's I had ever experienced.
So the point is, the collectors can make a HUGE difference, more so if something was not quite right previously.
And I have seen Marks work and he does great work and his performance is exceptional. He incorporates large sweeping bends with as much of a straight shot off the heads as possible, even if it means not being a "true" exact length primary tube design. To me, thats the way to make a header.