I recently got a PO to build some headers for a local race car manufacturer that builds several different spec racers. I was given a rough prototype set and some jigs along with all the mandrel bends and required materials. The collectors are premade by Hedman - and fairly rough with big mig welds and gaps in the stops and starts. I don't have dies for my bender in 1.875 OD, so using U bends was the way to go.
Fitting the tube pieces up in the jig:
Due to obstructions in the car the headers are installed as 2 halves as you can see by that last pic.
Welding up the primary tubes:
Welding the primaries into the flange:
I found the tubes flopping around on the welding table a royal pain to position, so I used a base from one of my homemade material stands to make a tube holder. It adjusts up and down, has about 180 degrees of angle sweep, and you can rotate the tubes in the v-clamp as well. This made welding everything up MUCH easier!
And here are some pics of the complete header assembly:
One done - 9 more to go! And, there might be 10 more following this first batch of 10!