[Tony Radford]

Wilf, sounds reasonable. If I'm not careful, this hobby will become a job! I found a website for a custom header fabricator in So. Cal who gives a bit of technical insight as to how primary tubes are sized. As is usually the case with technical papers, it sounds complicated. I think that phase I of my journey (400 HP to 500 HP) might as well include my existing headers and Phase II (500 to 600 HP) can include racing heads and the headers to match. At least that way, I can stay married and my daughter can stay in college.