Due to the concentration of heat that is built up in the manifold from the backpressure of a turbo hanging off it you have few choices.
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The best. 321 Stainless steel. This handles the heat and vibration the best and wont work fatigue over time like 304. If braced properly it will last a very long time with thin wall materials. (anything thinner than sch 10)
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304ss is best used at schedule 10 or thicker. It has shown to stand the test of time. Any manifold you see for sale now a days is usually sch 10 even the expensive stuff like Kevins or really any reputable name brand…obviously if it isn’t cast.
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Inconel, there is alot of misinformation as to the properties and application of this material. Inconel handles heat amazing, is strong and light. It however has a tendancy to carborize when a rich mixture hits it. Making it very brittle over time. It is used when the car is in perfect tune, run hot all the time, and not expected to be used as a daily item. (F1 race cars) Jets, turbines and other items use it where heat is more concentrated allowing for a complete and through burn. Or at least this was my understanding as explained to me by a Dr of chemistry and physics
edit: i love you gary lol be my valentine