It will be far, far cheaper to get whatever you want (I' m assuming a manifold) fabricated and/or machined than getting something cast. As mentioned, dies need to be made for something to be cast and this is not a cheap exercise by any stretch of the imagination. Wax or sand dies can be made up for one off's, but you need a prototype to make the die off of anyway so.....

Maybe rapid prototyping (3d printing) could be a goer for you, but you may have issues using the product in an engine bay and you would also need a 3d model of the part your trying to create.

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