You may know all this already but here are a couple of things I learned welding the exhaust. Keeping in mind I am not an expert on this, or anything else for that matter. 1. Use those beautiful polished 90 deg. bends (no straight sections on them) rather than the 180 degree bends some suppliers sell with straight sections on them. Those are terrible distorted right at the 90 deg mark and won't match up to pipe. 2. Make sure the parts all mate perfectly. Easiest to do with a belt/disc sander. 3. If the parts match perfectly, and you use a TIG welder, you do not need filler material and the welds turn out really nice. Playing around a bit with settings you get full penetration, little heat buildup and beautiful welds. Ideally you cap the ends and purge the inside with Argon, there are lots of u-tube videos on it, but you don't have to unless your in the racing industry. It is surprisingly easy, again, key are perfect joints, which goes for almost any welding really. The time you spend making the joint perfect you save ten times over when welding.