I figure I can do a pair of these for under $80 total, which is cheaper than the billet ones but still not cheap enough for me. There's gotta be a way to make them even cheaper.
I only ordered the one stack and I haven't tried it out yet, but it looks like it will fit, or can be made to fit, quite easily.
These are not very tapered since they're made from straight pipe, but they do have the nice rolled inlet.
Let me know what you think.

 

I think any part you make, or adapt from another bike, will need a lot of testing on a flow bench and/or a dyno before you could say it was an improvement over the OEM parts.

Are you intending to do that, or where you just going to try it and do seat of the pants testing?

 

the question is, does something like this need a retune of the carbs?

 

Seat of the pants all the way. I think the biggest improvement made by velocity stacks is a product of the rolled inlet. Of course, the length of the runner also has an effect.
http://www.profblairandassociates.co.../Bellmouth.zip

 

Absolutely.

As to how to make these things, an Australian VTR owner made some out of plastic. Not sure how he did it, or what specs he used in the design, but they sure looked good. Unfortunately they were found in his workshop after he was killed in a crash on his bike. But it shows that plastic is an option.