[vin63]

Having worked at a couple of header manufacturers and built many headers myself, I've always gone with mild steel and used a ceramic metallic coating - I have built stainless headers for specific customer requests. My reasoning for going with mild steel on my own stuff is the extreme heat cycles in racing that can contribute to heat-related fractures/failures in the more brittle materials and I don't live in a high humidity region. I see a lot more stainless headers develop cracks. My headers on my old Super Gas car showed no signs of corrosion or damage after 20 years of racing. My radiator hoses were made from the same mild steel tubing and were also ceramic metallic coated, and showed no signs of corrosion being subjected to water. I do run stainless mufflers on all of my hot rods, particularly Borlas. Stainless from the muffler back will help with the longevity of the system as you were asking about.