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I came across this video on youtube where a guy was making intake ducts using casting tape (as in what they use to make a cast on your arm or leg). Has anyone come across this? In the comments people were asking about issues with heat but it wasn't clear if it was in fact an issue. Thought it was an interesting idea. I'd imaging you could use foam or some other easily shaped material as the mold in the place of steel. Looks like a cheap, easy way for me to add ducts to my airbox?

https://www.youtube.com/watch?v=7rS7in5COiw

It is a reaction of alcohol and isocyanates to produce a polyurethane polymer on the fiberglass. I think if you seal it inside and out it would hold up to oils and abrasion.

I haven't found a good source for the silicon tapes used to make the hoses and adapters seen all over ebay, but they must be cheap considering the prices for the finished parts. These tapes are wrapped around a mandrel then heated and the mandrel removed.

There are also self vulcanizing tapes but they are expensive.

You could wrap your mandrel with a fiberglass tape or cut sheets. Spray contact adhesive on the tape before wrapping. Then mix some resin (epoxy or polyester) and brush it on. Pull mandrel and brush it on the inside. No need for casting tape prices.

You can make the mandrel from fleece for concave surfaces, hot glued at the ends. Clear coat the fleece so it wont take up the resin, wrap in sticky glass, apply resin and let it set up, then pull the fleece out and coat the inside.

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Thanks for the ideas miatav8. The casting tape isn't that expensive. I figured I'd try it out, so I received a roll of 4" x 4yrd for less than $20. As short as the ducts will be I should be able to do both with the 1 roll. I have some blue foam laying around so I'm going to make some molds from that. Unfortunately it's pretty low on the list priority-wise so it may take me a awhile. Although I'm curious about it and turning the ends of the exhaust to mate up to the engine is getting monotonous, so it may get moved up...