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.

[NickP]

I'd see if you could rent/purchase a small bottle of 100%. My last experience with MIG and Stainless with 308lSi (AKA 308LSE2) or (ER-308l [Hobart]) and 100% worked pretty well.

[WagonCrazy]

All good advice guys. Thank you.

I back-purged my tailpipes and the welds turned out much nicer inside.

Laszlo, explain this process more to me please

[NickP]

Pretty simple. You simply fill the innards of what you are welding using a plug at both ends, a regulator to feed argon (100%) into the chamber and proceed to TIG as usual. Be prepared to spend some bucks on gas.

http://www.millerwelds.com/resources/communities/mboard/forum/welding-discussions/11339-cheapest-way-to-back-purge-with-single-tank-of-argon

[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.

[MP&C]

We welded up mandrel bends (flowmaster kit) and Flowmasters, using stainless v-bands and MIG. Then owner powder coated using high-heat powder coat. Close match to the Jet hot of the headers. Not exact, but close..

[chevynut]

Steel WILL rust inside......stainless is forever. If the cost is the same why go with mild steel? IMO there’s no benefit. Combustion generates a lot of water. Headers run hotter than tailpipes. I didn’t think twice about going with stainless.

[NickP]

Steel WILL rust inside......stainless is forever. If the cost is the same why go with mild steel? IMO there’s no benefit. Combustion generates a lot of water. Headers run hotter than tailpipes. I didn’t think twice about going with stainless.

For the most part, I would agree that stainless would be the better choice especially if the price is the same. If price is not, give thought to the purpose of the car. Will it just be a weekend car? Will it be a daily driver or highway cruiser? If so, then longevity would garner thoughts of stainless versus carbon steel even aluminized or coated. Unless it's coated inside and out, rust (carbon steel) will begin its job of destruction.

[Custer55]

I Mig welded mine with steel pipes and stainless Magnaflow mufflers. I painted all the pipes with POR high heat exhaust paint which has held up very well with 2 seasons of driving on it. My headers are Sanderson block huggers with ceramic coating and the pipes connected directly to the headers show no signs of any paint failure.
Brian

[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.