boost tube
 

what exactly is a boost tube used for, the turbo? how does it go on, where does it go? just curious just trying to learn some things thanks

it is what carries the air or boost made from the turbo to the intercooler which cools the air comes out the intercooler goes into another boost tube that carries the boost into the intake horn and then on into the engine. they are connected with silicone boots. hope this helps good luck.

they replace the factory plastic 2.40" id piping with a 3.5" pipe, coming off the intercooler going to the intake.

If you are going to replace your boost tube, you should consider the grid heater relocate kit. The grid heater can be relocated in a upgraded boost tube, getting rid of two restrictions, with one modification.
I had already installed the bigger boost tube, so I relocated the grid heater into my throttle valve.
The path from the intercooler to the intake is a good place to start some upgrades, and a larger boost tube is easy to install.