I have been custom building exhaust systems for the past 12 years or so for myself. I have done a bunch of them and my personal preference is to completely weld the system together , with the exception of the axle connection, if it has tailpipes and i may need to remove it for repairs.
I have welded flowmasters and dynomax ultraflows with no problems at all. I use mig with er70s(if i remember correctly) and the dynomax are stainless 304. No problems miging to steel pipes after 10 years of driving/ racing.
Now to my question: i’m building another system for my 73 b body, and im trying the magnaflows , which i read are stainless. But, they dont state what grade stainless. Anyone welded these to steel ex pipes with er70s mig?

Thanks.

They’re 409 stainless. They’ll form a bit of surface rust but won’t see much difference in weldability.

Why are you using a 70 filler? Seems to me you are offering a nice exhaust solution that I like, but you are adding a rust band everywhere you close a connection.

I think I remember some type of liquid application applied immediately after welding that eliminated the discoloration and oxidation.

Joe

From what I remember anything other than 303SS should be passivated after welding to prevent corrosion. Passivation uses an acid to remove the iron that exist on the surface of SS to prevent formation of iron oxide (rust). I know we had to pickle (passivate) welding SS electric motor housings to prevent surface rust.

Thanks for the replies. I use that filler because i usually work with mild steel and the rest of the exhaust is steel pipes. What do you recommend for filler when welding steel pipes to stainless mufflers?

Maybe I misread your application, I was thinking you were welding ss to ss, if steel to ss, then my rust/cosmetic concerns are in consequential. I am not sure the filer alloy is that important ss to steel, as the weld will re alloy itself during the weld, and in most applications, this is not a high stress weld, but corrosion and long term thermal fatigue are more concerns. I recently did my Class 8 Semi out of SS 5" tubing, got tired of the a run Alum coated steel rusting thru. Tig is my method, with back purge, not sure what would be best for mig.

Find a way to use clamps on the stainless muffs

My exhaust is mild steel with Pypes stainless mufflers Welded with ER70 wire. I built the exhaust over 10 years ago, no issues ever. I'm pretty sure mine are 409SS, if they were 304 I would've used 309 filler and tig welded them on.

I did a little more digging around and learned that 409 ss will be magnetic and 304 ss will not. Even though i read that the Magnaflow muffler is 304, a magnet did stick to it. All surfaces including the pipe extending out were magnetic, so that leads me to believe it is 409 ss. In that case i will just mig it as usual like i do with the dynomax ultraflo welded muffs that are 409. Never had a problem nor fatigue/ corrosion issues at all.
Thanks for the feedback.