custom exhaust sleeves for NA
 

I have been looking at exhaust sleeves and I think I will give a shot at making a set so I can replace the factory turbo ones that are in there now.
What would be the best material to use as far as expansion rate, heat, durability ? the plan will include a custom header flange and piping to match the sleeves which by the looks of it will sit lower than factory and make it as much of a constant flow exit as possible.
If any one has or can make a set thats fine by me as well !!!

inconel