This exhaust is made of Inconel, this metal is considered a "super-alloy" and most of you will have never heard of it.
At over 10x the price of mild steel, over 2x the price of 321 Stainless, and roughly equal or a bit more expensive than the most common grades of Titanium, its not something most people will encounter in their daily lives.
Inconel is a name-brand of high Nickel content alloys. These Nickel alloys are commonly characterized by high corrosion resistance, fatigue resistance, and high strength, especially under extremely high temperatures. It can be found in blast furnaces, incinerators, and even Formula 1 headers and other racing and supercar exhaust systems. One of its most common uses is in the Aerospace industry. Inside all the hottest parts of a gas turbine engine, Inconel is used abundantly. Which is where I come in, and really the only reason this exhaust would ever exist. I work as a welder and fabricator at an Aerospace manufacturing facility and am one of the few people there certified to weld Inconel. I work with it almost every day building internals for GE jet engines, and from time to time, we have some scrap.
So now Ill get into the build for those further interested. It might get a bit lengthy.
I choose to clone a Doppler exhaust. Under the recommendation of a friend who ran a Doppler on his Gila'd E50 and loved it, even more than the MLM BK100 he had, I decided to get one for my Gila Tomos build.
Ohhh man, is that thing sweet! Major rippage for sure, but the exhaust hung awfully low and now I actually have a Motobecane that I want to use that Doppler on. So I decided I had to make my own exhaust. Its something I've been wanting to do for a long time and with the crazy amount of custom work I already had in this ped I felt it was the perfect time.
I started with getting some accurate dimensions-
Then over the next week I entered all the dimensions in Cone Layout, printed and cut out the templates, transferred the template onto scrap sheets, cut out, rolled, tacked, and welded 2 different versions of the chamber in 321 Stainless. (Which is the alloy of stainless that is the Aerospace standard for weldability, corrosion resistance, and heat resistance)
Originally I had wanted the pipe to come up the side like that, and had even started to redesign the flow of the pipe to make it work better.
But, after some fit testing and looking at my foot and leg position I realized that configuration just wasn't going to work. So I moved ahead with it being in a normal position and started to design the header.
The chamber is pretty easy to make, the header, not so much. I spent a bunch of time figuring out just what angles I need, putting in dimensions, printing out cones, testing how they work out in paper, going back and changing things, and doing it all over again. After a few nights of this I landed on the correct combination that would work well.
I then laid it out in Stainless, cut out, rolled, and tacked them up.
I mocked it up and everything seemed about right.
Except, the stainless was just too nice! It was coming out so damn shiny and perfect that I felt it didn't look right on my bike. I'm not fucking around here and I want everything to flow the way I want it to on this ped. Up to this point it was just a fantasy and a joke with the guys at work that I should make one out of Inconel, but I struck the jackpot one day while checking out our scrap dumpsters (which I regularly do). We had lazer cut a bunch of flame cones out of a large sheet of 0.032" 601 Inconel, and they way they nested left some decently large areas of the sheet unused. I hopped in the bin with a tin snips and cut out every large piece I could salvage.
I carefully laid out the cones to best use the limited material I had. Due to the lack of material, a couple of the larger cones had to be broke up into more than one piece.
I then re-made the same header design out of Inconel but concluded that it needed more design work to put a jog in the pipe that would clear the trans drain bolt, hug the frame closer, provide more lean clearance and just generally look radder.
It took another couple nights of plugging in dimensions and making paper cones to test and lock in the new design.
The segments ended up looking like this-
All rolled up and tacked together to test fit-
Once it checked out good I welded it all up and was ready for the mounting flange.
I had stowed away a scrapped 0.10" plate of 601 Inconel that I've been using just for fun projects. You might have seen it used in the base of last years first place Pinball Run trophy or in these welded gift cards I made for The Casserollers rally raffle prizes.
Anyway, because there was no 0.25" scrap I cut out 3 matching flanges out of the 0.10" material, welded them all together, drilled the holes, and ground it all to look like it was just a single piece. I then mocked up the pipe and flange on the bike and tacked it where it fit best. I had also made a mounting tab out of the same material and plotted its location.
Next the tab and flange were welded in place and I faced the flange to be perfectly flat after the heat warp of welding.
Luckily we make a certain part that uses a tube that is about the right diameter for a stinger, the only issue is that we never have any large scrap of this tube. The only pieces I could get were the drops from final length cut and fab. I made it work.
This Inconel stuff is difficult to drill and machine unless you really have the right stuff to do it. I drilled one hole, with a brand new bit, in a drill press, with lubrication, and the bit was toast after that one hole. FUUUUCK. Luckily we have a plasma cutter and I decided to just blow a bunch of holes in the stinger. It actually worked really good and was done fast. Its not perfect looking but no one will ever see it and it will function just as it should.
I made the baffle mount out of some 0.050" Inconel scrap. A strap was cut and rolled to fit inside the baffle, and welded to a round plate. I plasma cut a hole in that and then welded it to the chamber end of the stinger. Then I cut some straps and welded a stainless bolt to the end of the stinger to secure the baffle assembly.
I've been really wanting to use a Supertrapp style baffle because I have never seen one on a moped, they have some extra tuning possibilities, and they look different- cool shit. I've also been wanting to use this 2" 0.028" wall Titanium tube scrap that we have for a baffle, so I combined the two ideas.
The idea behind the Supertrapp muffler and its removable stainless discs is that you can vary the back pressure of your exhaust system. More discs = less back pressure, more top end power, and a louder exhaust note. Less discs = More back pressure, more low end power, and a quieter exhaust note. They are also spark arresting, so ya know, I guess if you wanna go blast some trails in a state or national park it would be legal.
I have a pile of Supertrapp Stainless discs from a junkyard find but they are 3" diameter. So I carefully bumped the end of the tube from 2" to 3" using a hydraulic tube expander with tapered fingers. I then gave the tube some more character by heating it with a propane torch in varying degrees to get some cool colors on the end. I had been holding on to a beautiful machined Titanium ferrule that was scrapped because of a little arc strike (we have very strict rules in Aerospace manufacturing) and I welded that on the end.
I seriously love welding Titanium, its a bit stressful and a pain because it pretty much has to be absolutely perfect, but when you get it right it is so rewarding. Done correctly, you can produce perfect welds that look like they were polished.
I made a cap out of stainless that is a tapered fit into the Titanium tube. It is the piece that allows the whole assembly to be held on by just one bolt. The cap also blocks in the fiberglass packing and has some posts to support the stainless discs in place.
The end dome is another stainless scrap piece that is made from an assembly that gets cut off in fabrication. Having all this scrap on hand is obviously very convenient!
The whole assembly is held in place with stainless hardware; a washer, split lock washer, a nut, and acorn nut tightened against one another. Where the ferrule meets the baffle mount I cut a cork gasket to make sure it has a good seal. I packed it up good with fiberglass baffle material and closed it up!
So thats that. A couple months of designing fitting, testing, and all that good shit and here it is, all finished up! In the end, the pieced-together design, less-shiny look of the Inconel, and they way it welds kind of dark and muddy was what really made it work, and was what I wanted for the look of my ped. I'm extremely proud of how it came out. I hope you all enjoy the work and the write up, I know I did!