See the other threads, there are plenty of them running around.

is all custom

Yes they do because they prevent hot air from being sucked by the air filter.

They can lower intake temps by at least 20 degrees.

Later,

they are supposed to work. you can build one and see for yourself. if it doesnt work you havent lost much depending on what materials u use.

If anyone has a design for them i work for a sheet metal company and can get aluminum (which should work the best) and the tools to make them for much cheeper than what they are charging at the other sites