[Craig T]

I spent countless hours over two days with a 3.2 911 race car on the dyno swapping different headers and collectors while Steve Wong (911Chips) worked at fine tuning on his laptop. We compared 1.75", 1.63", and two and three-stepped stainless steel tube diameters, all open (without mufflers) to keep apples to apples. All had their strengths and weaknesses somewhere in the RPM range, but non produced more than 2% in additional HP anywhere in the range.

I think a good off-the-shelf long-tube vs. a custom tuned long-tube would not be more then a couple HP difference...and the 4 or 5 additional HP would come at a huge cost.

EDIT...SW could make a better improvement with a few taps on his laptop keyboard to optimize A/F and timing than any header could produce on it's own.