Welding
From GummyCarbs
Exhausts
Material
Once source mentions 14-gauge stainless steel.
Joints
Hooker Headers makes "Hooker Headers Alignment Weld Sleeves". These can be used to more easily align and butt-weld two sections of tubing (found in this Street Shopper article).
Tubing
- Global Tech Engineering sells stainless elbows at a reasonable price. (e.g. 1.5" 304 stainless 45-degree elbow, 7.5" length, $5.65)
Materials
This thread states that most exhaust headers are made of 304 stainless, but the poster suggests 304l or 321/347 instead.