Stainless Header Flange Bolt Hole Clearance to Prevent Shearing?

[oldwestracing]

I'm building a set of headers out of 304SS with custom flange to fit the port (Brodix BR7 BS CNC ported by Greg Good). Considering making the flange out of stainless instead of mild steel. Since stainless grows more than mild, what is the consensus on how much clearance to give the bolt to prevent shearing? This is on an LS and the flange will be split so only two pipes on each flange.

I'd prefer to have them pretty close tolerance to the bolt to self align, but I could work something else out to align them if the clearance needs to be substantial.

[Rick!]

When the flange heats up, the holes also expand. It’s impossible for the circumference of a hole to get smaller when its parent material is heated uniformly. Knowing that, look up what a standard precision clearance hole is for your chosen fastener and use that. If u use stainless fasteners, recheck them frequently and replace them after a few retorques.

[Tom68]

Not sure if this is a serious post from Oldwest ?
Bolt shearing header flanges, LS bolts break when you undo them from being put in dry and doing 300,000 miles.

You need clearance holes especially if it's a one piece flange.

[modok]

I think it will shrink and warp more when you weld on the tubes as compared to how much it expands and contracts on the engine.
Perhaps 0.5mm clearance, oval holes as needed to achieve full wiggle of bolt in all holes when test fitting.
Ever heard the advice about never use two dowel pins to locate a part? Seen those bladed dowel pins?
Middle one tight and the others loose. Middle one tight others oval.
is this machined? or just waterjet?
You might be overthinking this.
Now you made me overthink it.

[oldwestracing]

Thanks everyone. It was a serious post, though definitely overthinking things. Everyone has their "superpower" and mine is creating issues where they probably don't exist. I suspect making the holes "tight" will be more of an issue for getting them off and on than anything else. I can located the flange in the right place each time with other means pretty easily.