Hey there

Hello, and welcome!

I'm actually rather new here myself, just been lurking for a while but your post caught my attention as I am also interested in building carbon fiber snowmobile parts.  I'll start by saying that I am still learning and definitely not an expert yet, so I'm not sure how much help I'll be able to offer, but I've been researching these things for a while, so maybe there will be something that can help you out. 

I am a little curious though, what is your skill level with composites parts/fabrication?  Also, just out of curiosity, what sled(s) are you working on? 

I've got a whole list of parts I'd like to build, but have been trying to start with simple things just to get the hang of it.  So far, I've only made a thin panel that will be used to help relocate the airbox on the throttle body, and a couple of small plates to replace the steel plates that originally sandwiched the steering shaft to the frame.  I had some excess resin and fabric left over when I made the thin panel for the airbox so I decided to make the other parts with it. 

A few more things on the list of future projects are:  Tunnel, float plate, body panels, headlight cover.  Obviously I want to have a good idea of what I'm doing by the time I get to the tunnel, so I've still got a ways to go. 

As far as how the composite rails for the rear suspension are made, I'm pretty sure Nextech is compression molding them, though I am not sure if they just add a little extra material in those areas and it gets pushed into place once inside the mold, etc.  It's also possible (though I'd think a lot less likely) that there is an excess of resin in those wider areas, making up part of the profile/shape. 

Depending on your experience with composites, I would most likely start out with smaller/flatter items, maybe some tunnel/running board reinforcements.  Another great starter project may be to just make some thin, flat panels to mount on the inside of the existing tunnel to help prevent snow from sticking.  Patrick Custom Carbon has some of these on their site, if I remember correctly.  Once you get to the point where you actually build the entire tunnel out of carbon fiber, you could still use the tunnel/running board reinforcement pieces to enhance the strength further, and the flat panels on the inside of the tunnel could be sold off with the tunnel (or separately).  That way you get to make some things (that are actually functional) while not getting too deep into the project. 

Hopefully this helps a bit in at least giving you a few ideas of which direction you'd like to start with first! 

I tried to upload a couple pics of the steering shaft plates I made.  I'm sure they only saved a small amount of weight, but most importantly, it allowed me to start learning more with minimal cost/risk.  If they don't work out, I just put the steel ones back on and chalk it up to a lesson learned!