that pipes the same, but the collector's different than the one I have, Mine are both 2.5 outside.
Can't find the actual tips I'm talking about, but here are some similar, but different brand
http://www.amazon.com/b?ie=UTF8&node=13675641&me=A1MK3HAFHEKCQUI'll stop by in the afternoon and check what brand and sizes they have available at the local shop.
I spent some time there the other day checking out mufflers and tips, but was looking for 2.5
can't remember the brand name on them right off, but know it was a familiar name brand.
seems like that's a double wall AND metric pipe (2 1/8 is ~60mm isn't it?)
If so, you -may- be stuck using a factory muffler, or a reducing sleeve inside the muffler.
If you have a well equipped muffler shop nearby, they should be able to neck down a section of pipe for you to use as a reducer.
Home built is easily done with a strip of steel wrapped around then slash or 'V' cut the ends so they butt smoothly together thickness to fit.
You have that shoulder on the collector so you should be able to butt the muffler up against it to keep a clean look.
Also, the 4 into 2 into 1 is generally called a tri-Y, made famous mostly by Shelby in the mustangs
Has me wondering now, I'm working on a deal to get an F with a bad muffler, was expecting to be able to use the same arrangement I have on the two other bikes, may have to change plans!
Ken.