So tonight I made up a megaphone exhaust for a mates XR250 supermoto that we're fucking with more than slightly and I decided that seeing as most people here probably haven't seen much in the way of sheetmetal fabrication that I would take a couple of photos to show how it's done.

I have another megaphone to roll tomorrow too so I will get someone to take photos of me as I'm working on it so that you can see how to correctly use the necessary tools.

The first thing you need when rolling up a megaphone is a sheet of steel. I'm a fan of 0.8mm thick myself, but up to 1.2 will work fine and gives you more material to grind back when you are cleaning up your welds (something to keep in mind if you aren't hugely confident about the finish of your braze).

After you have your steel you need to cut out the shape that you are going to roll into your megaphone. I'm going to link you to a page that will describe howto do this just as well as I can, but this way I won't have to type as much. :D Basically, you work out your pattern, make a template on cardboard, transfer it to your sheetmetal and cut it out (jigsaws, nibblers, grinders and guillotines all work well).

Here: http://search.sheetmetalworld.com/news/articles/198.cfm

I use these bad motherfuckers to cut my sheetmetal out.

http://i2.photobucket.com/albums/y21/brownbomber/00001-8.jpg

The next tool you will be needing is a set of sheetmetal rollers, like these ones that I made earlier. To operate them you basically just apply more and more pressure to the sheet by lowering the top roller, until your edges meet up. You can also notice that I have machined my top roller into a taper, which will allow you to hammerweld directly on the roller, meaning you get no distortion in your exhaust.

http://i2.photobucket.com/albums/y21/brownbomber/00002-8.jpg

I like to use an oxy-acetylene torch to nickel braze my cones. The trick is to beat the edges of your sheetmetal so that you create a valley where the two edges meet, then fill this with braze, which allows you to grind it back to reveal a smooth surface with no visible weld.

Here is the one that I just finished before. It's not the best but it will give you a rough idea of how it should go. The welded edge is to the top in that photo.

http://i2.photobucket.com/albums/y21/brownbomber/00001-9.jpg

As I said, this is fairly rough and ready at the moment. I'll get some more pictures when I roll up the next one (gotta have a spare) and make this thread as educational as a motherfucker. I'll go into baffling when I get up to that stage too (my baffles don't lost hp).

:)

Cool, but probably won't sound much different from straight pipe

Cool, but probably won't sound much different from straight pipe
A baffle goes inside it man. You'll get a hell of a lot more performance with a megaphone than with a straight-through pipe. The shape of it allows the engine to scavenge sexily.

Try making a muffler from sheet copper for your XR250.

I have heard one, it sounds real good, real distinctive.

Also where the hole is in the exhaust.
Get a bunch of round tubing, like 10mm ID & arrange them in a honeycomb sort of pattern & stuff them in the hole & weld them in.
Seen that too.

Try making a muffler from sheet copper for your XR250.

I have heard one, it sounds real good, real distinctive.

Also where the hole is in the exhaust.
Get a bunch of round tubing, like 10mm ID & arrange them in a honeycomb sort of pattern & stuff them in the hole & weld them in.
Seen that too.
Copper is heavy dude. It's way too malleable for me to want to use for anything like that too, it'd lose its shape very quickly.

A bunch of round tubing for a baffle also weighs a fuck ton, it wouldn't be very good for exhaust flow either. Generally I just roll a sheet of perforated sheetmetal into a tube, weld the seam together and wrap it in fibreglass. Sounds great and is great for flow. You can fiddle a bit with them while tuning too, changing baffle lengths, rolling them into reverse cones, closing up the entrance to them etc.

The Copper only forms the megaphone part of the exhaust, the last 400mm - 500mm. It won't add much to the weight, looks different too.

That gives it the real distinctive sound. It never rusts out either.

Oh, the bunch of tubing is only 1 inch long (or even less), its just visual, its not to silence the exhaust.
It just fits in the opening.

I had a XR250 with these mods, thats why I think its a good idea.
The copper exhaust part goes real well with the sound of the XR.

Wish I had a XR again.....

:(

I need to fix my bike