Does anybody know what grade of material was used to build the factory headers? I think it is a stainless of some sort. But I know its not 304. Is it maybe 409? I'm going to be doing some welding and want to ensure I use the correct wire.
Check it with a magnet. 409 the magnet will stick, 304 it will not.
Standard ER70S wire works fine in a MIG. It is considered weldable stainless. It can even be gas welded with a carborizing flame. BUT.....no matter what process you use, it WILL crack again. Just a matter of when, not if.
Bead blast the area to be welded and TIG with inconel rod.
The stock 86-87 headers are 410 grade Stainless. I have scanned a couple of sets with a PMI and they all come back as 410. Yes the best weld repair is done with Inco you just have to watch the post weld heat to keep the weld from cracking. Using a backing gas or not has shown no impact on the thin wall tubing of the headers. The biggest factor we have found in keeping the headers from recracking is post weld stress relieving in an oven at 1200 degrees for 1 hour and control cool over the next 4-6 hours. Just what I have done and works well. Jon Hanson
When you say controlled cool do you slowly cool them back to ambient?