Cast iron can be incredibly difficult to weld, especially a manifold that's undergone thousands of heat/cool cycles, so be sure whomever does the welding is very capable. Nothing says "you're having a bad day" like an irreplaceable piece of cast iron that just won't take a weld. I got involved in a repair job on a huge centrifugal pump housing that had thrown a piece of the damaged impeller through the side of the pump. The lead man on the job was an oldtimer with 40-something years of experience welding cast iron. We scavenged up all the pieces of the broken casting we could find and pieced them back together like a jigsaw puzzle. It took three days of heating, peening and slow-cooling the casting, making weld beads with nickel-alloy rod of about an inch long at a time. The outlet pipe of that pump was 16" in diameter, and the bowl we were welding on weighed about 400 pounds.
Jerry
