Let’s have a quick chat about back purging. A lot of welders don’t back purge when they weld stainless and claim it is fine and never have an issue. Of course, shielding the back of the weld on stainless will absolutely make for a stronger weld as it will eliminate sugaring. The point people usually like to argue is it is not strictly necessary to back purge an exhaust for it to last.
There is a good reason why roll cages are made from round tubing. Round tubing is inherently strong in all directions due to it’s shape. Oval pipe is different. Due to its shape, oval pipe is weak in the vertical direction, which is the direction that inherits all of the force when you bottom out your car doing sick jumps.
Mr. Kojima himself reported that they had multiple issues with the oval exhaust cracking on Dai Yoshihara’s Formula D S13 until they started back purging it. For this reason, we will be back purging this whole exhaust.