Dennis, where do you get your CF from? I've bought from a place called Dragon Plate. For a bar, you could sandwich layers of CF and have a steel bar(or whatever material you use) wrapped around the outside. I've worked on many cars that have CF chassis and body panels. That stuff is durable when done right(look at NASCAR, Indycar, and Formula 1 cars) and provides tremendous weight savings over metal components.
If you only made the expansion chamber out of CF (would that be any weight loss?). I have no clue if it would perform as well as the steel pipe or take the heat..?? Form two halves using a female mold (so you can vacuum bag it) .....trim edges and bond the chamber together with a bit more CF. Do you have access to a CNC mill?
Another thought....if the CF can take the heat.... and you have access to a CNC mill.... make two female molds.... (mirror images) Layup, trim and bond the whole pipe!
I worked in the plastic vacuum forming industry for a while. Probably where some of my thoughts are coming from. I've also seen how CF bicycle wheels are formed.
Have you tried carbide cutters? They might last a bit longer than the HSS ones. Or maybe you're using carbide....
Here's some progress.....new oil tank, gas tank, billet back handle, a few holes drilled in top handle and side plate. Cylinder,head and pipe ceramic coated. Should be testing shortly.