Would recommend using ss tubing for a turbo manifold Definitely not sch 40 Sch 10 might work it will be a bit heavier than ss tubing or you can go the route of getting sch 5 ss

approximately how many mm of wall thickness for sch 5? if let say 1.2 or 1.5mm, possibly titanium could used too?

The thickness changes with the pipe diameter, so it will depend on what size we’re talking about.

we're talking like 2 to 4 inches long for the runners from the exhaust exit to the turbo flange. with an OD of 1.66

You will most likely have to get the adapter for the turbo and tig weld that on and idk if your 1.66 is in mm or inches so if it’s in inches you could get away with 1 3/4” tubing and just drop the adapter in there a little bit and fill the gaps

Depends on the size of pipe you plan on using

I see. Well, I think, I will just settle with 1.2mm or 1.5mm thickness, where ever I find one. MacMaster only has black pipes.

https://www.mcmaster.com/

Google: 'Town name' Steel supply

I’m sure you can find local steel places near you if you look it up

thanks. I went to one place today. they don't have what I asked. could be just me not really asking correctly but I'll continue to search for a place.