This weeks task was to create the header. My original plan was a caterham style exhaust with the collector on the outside. However after receiving my tubing kit from columbia mandrel, I realized that I would not have enough tubing to complete it, that it was going to be a pain to run it and clear what needed to be clear, and since I was using stainless it was going to cost me another $100+ for the additional tubing.
So i started looking at the miatas header, and since that is generally considered to be the optimum config for that engine, I went about replicating it with my requirements. The main requirements being that I wanted it to move over the steering shaft, so that I could remove it without taking apart a good chunk of the car. It needed to pass underneath the supercharger with enough clearance, so that I could wrap the header to prevent heat transfer to the supercharger. And that I could get the collector high enough that I could get (2) 2.5″ 90 degree mandrel bends out the side of the car without coming in contact with the chassis and without have the side exhaust pipe sitting to far from the chassis.
Here what I made. Cylinders (1 and 4) and (2 and 3) are approx equal length. Which is how mazda did it.
What I learned from this adventure:
Stainless Steel is harder to mig weld. Not drastically, but enough to be slightly be off putting with the visual quality of the welds. In hind sight I should have tacked and had someone tig them. But since the header will be wrapped it doesn’t really matter.
You really need something to mock these up. The method I used here was to make the center 2 tubes first since they were more or less straight shots. This allowed me to get the collector into its position, then I worked 1 and 4 to clear the supercharger. I used some wire loom to figure out the direction needed on 1 and 4, which helped a little.
In the end I’m happy, mainly that it’s done and doesn’t look like a disaster, I may still need to take it to someone to weld up the center of the collector as I have some concern that the slip fittings may not have been tight enough, and I can’t get the mig in there to do it myself.
Not quite done for the day, with the completion of the header, I went ahead and built the exhaust. Only thing left to do is attach the muffler to the body somehow.