Turbo Manifold 321 or 321H

[innovator]

I am going to build a turbo manifold from butt weld fittings (1 1/2" NB SCHD 10)

I can get 321 fittings in normal or high carbon (which the specs say is for greater strength). However 304L is recommended over 304 for lower temperature applications where the low carbon content is benifical.

So when using 321 which should I use, normal 321 or 321H?

 

[Tmoose]

I'd get the ones that are cheaper and/or more readily available.
And several spares for welding practice

If the manifold has short runners and is stout the nominally 50% greater thermal expansion compared to steel or iron may require counter measures to prevent overtaxing the mounting studs or even just keeping gaskets alive.