If the weld is poor on either it'll pull itself apart.
What happens on header flanges is that mild steel won't force the nuts, studs, bolts loose over time. Nor will it break them off. Sometimes stainless can. Also, it won't warp as much during welding. Which is alot less stress on the manifold once it's installed & torqued down, then heated. (Tho "don't warp the workpiece" can be applied to anything you ever build. :006
Only real disadvantage of mild is that it won't take quite the same temp for raw failure, and it rusts. You can fix both of those. =)
Or just you know, but stainless & do a good job welding it!
What happens on header flanges is that mild steel won't force the nuts, studs, bolts loose over time. Nor will it break them off. Sometimes stainless can. Also, it won't warp as much during welding. Which is alot less stress on the manifold once it's installed & torqued down, then heated. (Tho "don't warp the workpiece" can be applied to anything you ever build. :006
Only real disadvantage of mild is that it won't take quite the same temp for raw failure, and it rusts. You can fix both of those. =)
Or just you know, but stainless & do a good job welding it!