I was offered a choice of fiberglass, aluminum or Kevlar, so I went for Kevlar on a whim. It turns out to be light, rigid and easily worked, as I found out when I went from 45s to 48s and had to open up the holes.

To get the features in the right place initially, I mounted the carbs and did a pencil rubbing on a long piece of paper. This is then easily transfered to the material of your choice.

My main purpose was simply to feed the engine cool outside air instead of hot engine-compartment air, and also to have a graceful way of mounting an air filter compatible with the long horns, so I'm not very clear on the theory of the thing beyond that. What I've been told by several people is that it works sort of like an exhaust system in reverse -- once air in the tube is set in motion, it's mass that tends to keep moving, and that reduces the pressure drop at the carbs -- it may even supply slight pressure in some conditions. That's why the smooth tube is important... you wouldn't use accordion tubing in a hi-po exhaust system, right? In my case, the exhaust is 3" diameter, so that seemed appropriate for the intake as well.

I can't vouch for the accuracy of that theory, but it makes sense intuitively. I had originally wanted to put a rubber flex coupling in the tube somewhere, but there simply wasn't room to fit one in. There is a certain amount of float built into the tube/box junction, so I've had no problems there (I've got some hefty foam rubber wired around that junction so dirt can't sneak in).

One downside is that it's useful for tuning purposes to be able to hear the pitch of the intake roar, and there isn't any audible from inside the car...

Hope this helps.