I've decided to have a friend's brother make me a custom manifold just so he can start up his fab business. I'm looking at flanges from a lot of different vendors and got a few questions.

I've been seeing "3D contoured flanges" on a lot of reputable vendors. I'm wondering if it really made a difference in performance compared to non-contoured.

Been also wondering if I should go with 1-1/2" piping or 1-1/4".

Thanks in advance.