Frank - are you MIG welding all your exhaust components? I have read tri mix is probably the best but 98/2 is a decent alternative. I have done stainless welding with 100% AR and its gotten the job done but it isn't a nice bead and the welding is a bit fickle.

I'd really like to pick up a Thermal Arc 95S with TIG torch kit for this kind of thin wall welding and use the MIG for tack welds and mild carbon steel only.