Porting Manifolds, how thin is too thin?

[DRP67207]

I've been doing some work on a spare exhaust manifold I have lying around, port matching and smoothing things out, and am curious about how much thickness I need to leave in order to prevent cracking or other damage.  I've been searching here and elsewhere and see lots of comments about "don't go too thin", but no explanation of how thin is "too" thin.  Any advice on a value not to pass? Thanks.

[arb]

I've been doing some work on a spare exhaust manifold I have lying around, port matching and smoothing things out, and am curious about how much thickness I need to leave in order to prevent cracking or other damage.  I've been searching here and elsewhere and see lots of comments about "don't go too thin", but no explanation of how thin is "too" thin.  Any advice on a value not to pass? Thanks.

Are you going to hang a turbo off it ?  I've never seen one crack, but I'm sure they will if too thin especially if you have a turbo hanging off it. If not, you can relieve some of the stress by using a SS flex join after the manifold .