an aluminum pipe and aluminum header
Kali, the pipe isn't aluminum. It's aluminzed steel. Aluminum in that thin a material would be almost to the melting point when the exhaust hit it at the head.
Regarding "heating and stretching" aluminum.
You can't really "stretch" aluminum. You can bend it and form it, but only a small amount. This can only be done by professionals.
Heat treating aluminum must done after any other process involving heat to small areas -- like welding. If you weld a piece of aluminum, and don't heat treat it, it will break right next to the weld.
Heat treating isn't something that's easy to do. Most of the time the only place you'll find a shop that does heat treating is someone who works in the aircraft industry. Fortunately for BBR, Boeing and all that is right up the road from them.
For anyone else messing with aluminum, play at your own risk.
Kali, BBR told you the YZ80 rear end wouldn't work because they didn't feel it worked as well as theirs. I can't tell you how many times I have people call me back about a problem and say "You said it wouldn't work, but after spending lots of money and getting a bike to work half as well as it should, I made it work!". I guess that sometimes it's easier to tell someone a conversion won't work, rather than tell them all the reasons it won't work AS WELL as other options.
The setup used by Yamaha for their project may be made up of parts from the YZ80, but there's no way to know how they made it work. The chassis may be completely different.
I can really understand why BBR doesn't participate in the forums any longer, when we hear things like this:
that information came straight from the BBR tent at the Glen Helen races! From a source there who told me that he had to have the swingarm heated/stretched and re-fit for the disc brake he was running on his TTR.
Without knowing who said this to you, all I can say is that with your short time in this field, you misunderstood what they said.
Don't take this wrong, Kali, but if Chris or Duane Brown describes a process to you, you may not have the basic knowledge of the subject that's required to understand their explanation. This isn't a slam on your intelligence, only saying that it's like Triginomitry, you have to know Algebra first before you understand it!
Here's what they meant by heating/stretching. People refer to "stretched swingarms", they don't mean two people pulling on either end, like taffy! They mean the swingarm is cut, put in a jig (to keep it aligned) and a piece of material is welded on to make the swingarm longer. Heat treating is then used to un-stress the metal after the welding.
Without understanding the basics of this process, you got a mental picture about metal being "stretched". That is the information you passed on. Not intentionally incorrect, but incorrect nonetheless.