There is a lot of research that goes into the fabricated intakes. Things like runner length, runner volume, port configuration, primary and secondary wave tuning, air flow tuning, fuel flow tuning, plenum volume, carb configuration and layout, boundery layer friction and probably a few other things all figure into their design. An added benefit is also maintaining a cooler charge as well. Running air and fuel through the runners cools sheet aluminum a heck of a lot fasater than it can cool a chunk of cast aluminum. These intakes are thoroughbred race pieces. With price tags around $5000, I can't imagine there are many of us willing to run one on the street.
