Downpipe Turbo Flange Preferred Material
 

I have a Stainless Downpipe that will need a new flange to mate the Turbine Oulet. I understand that the recommendation is no gasket. My question is: should the flange be Stainless like the DP, or Mild Steel to better match the coefficient of thermal expansion of the Cast Iron? Subi TD04, and BEGI Segregated DP.

It should be the metal you're welding it to.

Is the downpipe ebay? If so, consider it to be made of cotten candy, and it doesn't matter.

If you know it's good stainless, just get a 304 stainless flange... In fact, good luck finding anything other than a 304 flange for stainless.