i made my own exhaust using the mig stainless wire and argoshield light,unless you use pure argon it will be slightly black but works perfectly well.turn the amps and wire feed up and pulse weld it.it will spatter unless you use anti spatter spray.if you going for a shiney magazine look exhaust then its worth using some.
if you look down the the exhaust you can see there is good penetration but also not alot of weld on the inside,not bad considering I didn't purge weld it.