I've asked the same question as starchland... most of the "cold air" intake systems have polished aluminum tubing and aluminum is a great conductor of heat. I make all of my tubing out of fiberglass, a poor conductor of heat. Also, like the systems posted by SK2 ok, the air filter is enclosed so as not to draw under hood temperature air. One of the systems I made had an box large enough to place dry ice in the bottom. It worked... dry ice has a temp of -109.3 and the butt dyno results were noticable but not amazing, plus it's very impractical for everyday use. According to another forum, there aren't any gains to be had from aftermarket intake systems but there seems to be adequate information on this forum to dispute that. I'll keep searching. Like ans2K says, I'm wondering if the above noted designs create some kind of pressure effect by virtue of their shape and if the hood has to be cut.

 

Yes, those shapes are intentionally goofy. The varying diameters cause the air to swirl and increase in velocity. This helps bring in more air, and to make the air already there more useable by the motor.

There is a crux, and it's that at very high intake volumes (read: high RPM @ WOT), those become a choke point. They do help at engine speeds and loads in the low and mid-ranges, but up top it will stunt horsepower.

For a street car, that's fine. You spend very little time at WOT. On a race car that is spending all its time at WOT near redline, this sort of intake will undoubtedly cause the car to fall flat on its face. Those guys just run cheap and simple intakes to let the motor get as much air as quickly as possible.

 

I gutted my stock box, it sounds better and cost me but 2 hours of my time