If it's the same stuff I got with the muffler, Rotax supply a stainless "donut" so you can cut whatever curves you want out of it, as well as straight tube. I did the cutting myself based on a wooden mockup of the engine then got an experienced welder to join them. Having said that I was slightly too long in one so had to re-cut, I need to either get him and his welding equipment here to do it in place, or take the lot up to him and hope that it fits after. I think I'll try to get him here.