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I'm no expert but I think it depends on the area, a flat area will bow, a corner or weld could blow out but a runner is more curved and would withstand more.

I have sections of 1.6mm tube, whilst not cast i think it's super thin and it takes 30psi.

It's a major pain make some block off plates and use some shop air to test it
 

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There are several things to avoid on a pressurized, cast intake:
  1. Large flat areas - these literally stretch deform without a lot of pressure, Force = Pressure x Area
  2. Sharp corners and poor transitions where the runners meet the plenum, or the TB transitions to the plenum,
  3. Cast alloy and available heat treat - 360/380 is cheap but weak, A356 is heat treatable and is a better choice,
  4. Casting method (investment or sand), or more specific, how the cores are made. Newer printed cores are more accurate but also more expensive.
I've done analysis on several versions of pressurized, cast AL intakes for V8s and around 6mm not including ribs is where they end up.
 

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I think stress fatigue over time is another factor to consider. I have seen a few "over ported" intakes that probably would not fail immediately but y some point they were bound to rupture. I welded them up on the back side to not effect porting but couldn't be the last person to touch it and be associated with the eminent failure.
 
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