Tack welding stainless steel with a Mig welder

[WagonCrazy]

As I approach the purchase of the exhaust components for my Nomad build, I'm faced with a choice of materials to do this in (mild steel, aluminized steel or stainless steel).
And I'm faced with a limitation of only owning a MIG welder.
And I want to fabricate it myself, using mandrel bent pieces that I can get online.

So the main question here is "can I spot weld stainless components together with my MIG welder, then remove the system from under the Nomad and take the pieces to someone for complete Tig welding?
Does it screw anything up to fabricate it all under the car first, by carefully spot Mig welding each piece as needed to be satisfied with the whole system layout, and then dissasemble/remove it all and take it to a buddy for Tig welding "on his bench"?

Some aspects of this exhaust build I've got sorted out, like going with a quieter muffler like Flowmaster 50 or Magnaflow 3xl. Both are 3 chamber style mufflers, much quieter in interior drone than the equivalent 2 chamber mufflers that have been so popular over the years with builders. Both seem to be made in either stainless or mild steel. And I'm OK with sacrificing a little HP with these quieter mufflers for more enjoyable cruising.

Deciding between going with 2.5 inch or 3 inch diameter system also. I'm only running a bone stock 340 horse LS1 engine/T56 trans, and don't plan to ever have more than 500 horsepower in this thing.

Let's start here. Give your opinion on exhaust materials and the welding question above.

[55 Rescue Dog]

I tack weld stainless all the time with a MIG with steel wire using 75/25 gas. Tried stainless wire which works, but spatters more. It can rust a bit with steel wire.
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[chevynut]

I don’t see anything wrong with tacking with mig. I personally would use stainless wire that’s recommend for the type of stainless you’re using. You could even weld the whole thing but tig gives much nicer welds. I back-purged my tailpipes and the welds turned out much nicer inside.

[Rick_L]

You can tack weld stainless just fine with a mig welder and carbon steel wire. Thing is, the welds will rust eventually, actually sooner than later on an exhaust system. The hard way to prevent this would be to tack weld everything again with tig and SS filler wire, then grind the mig tacks to removed the carbon steel filler. You probably will still have a contaminated weld though.

Why not try to find a spool of stainless mig wire for your mig welder and try it? I think what you want is 309 alloy stainless, at least that's the filler I use for tig with 304 and 321 stainless. The cost of a small roll won't be much. What I don't know is how your typical 75/25 mig gas for carbon steel will act.

If you're not going to have stainless mufflers (you mentioned Flowmasters) - why not go with steel tubing too? You can probably do it with steel and ceramic coat it for about the same cost or lower than stainless. Something to consider if you haven't bought tubing yet. That's the way I'm going - the headers and fabricated tubing will be carbon steel, ceramic coated - but I'll just leave the mufflers aluminized, and use high heat paint on the flanges I weld to the mufflers.

[WagonCrazy]

If you're not going to have stainless mufflers (you mentioned Flowmasters) - why not go with steel tubing too? You can probably do it with steel and ceramic coat it for about the same cost or lower than stainless. Something to consider if you haven't bought tubing yet.

Seriously thinking about going in this direction Rick. The hooker long tube headers are just mild steel, so why bother with the rest of the system being stainless? I'm really not sure what the cost of ceramic coating for an entire dual system is, but geez...I've spent so much to date that I've just stopped adding up receipts.

So If I go with mild steel all the way (including the mufflers), then I CAN weld it up with my Mig and call it a day. I also found out that i can get VBand clamps in mild steel also (well Im guessing the weld on bands are mild steel and the outer clamp ring is stainless...so that works), so I can weld up this system entirely after I fabricate and tack it up.

[Rick_L]

Most of the V band clamp flanges are stainless also but you can weld them to carbon steel with whatever technique/filler material you like. Just coat or paint when complete.

[BamaNomad]

ONE more opinion of stainless: Stainless pipes are generally thinner metal than the steel ones, and much thinner than aluminized, and that 'lack of mass' comes thru in a 'tinny SOUND', which I personally do not care for... and that is why I'd use anything OTHER than stainless..

[NickP]

In all of the units we built, we kept the proper gauge/wall thickness but to note, we never buy kits in a can.

[chevynut]

Stainless pipes are generally thinner metal than the steel ones, and much thinner than aluminized,

That is simply not true. My exhaust pipes are 16 gauge stainless which is at least as thick as any commonly used mild steel exhaust pipes. Sure you can buy thinner material but 16 gauge is common. And it STAYS that thickness because it doesn’t rust. Most exhaust systems on newer cars are stainless.

[BamaNomad]

That is simply not true. My exhaust pipes are 16 gauge stainless which is at least as thick as any commonly used mild steel exhaust pipes. Sure you can buy thinner material but 16 gauge is common. And it STAYS that thickness because it doesn’t rust. Most exhaust systems on newer cars are stainless.

CN? Who sells stainless exhaust systems for older cars made of 16 gauge or thicker? I know you can purchase your own SS in whatever thickness you want and roll your own, but my comment was related to the 'off the shelf' SS systems sold for 'restoration purposes' for classic chevys and other cars, corvettes, etc from the fifties/sixties/seventies... and they sound like CRAP... but that's just one man's opinion, and we all have one.