As you all very well know, brakes are what makes the car stop. In racing you want to be going as fast as you possibly can for as long as you possibly can. This means that you want to stop quickly. The easiest brake modification you can make is brake pads, these are the pads on the calipers that grasp the brake rotor. Secondly you car replace the rotors with drilled and/or slotted rotors so that they dont heat up and work less effectivly.

If you want to stop really fast, you should get a big brake kit. The STi already comes with a brembo big brake kit, however there are better kits out there. Companies like Mu Racing and Rotera offer very high quality big brake kits. These kits come with calipers, lines, pads, and rotors.

This is an example of a slotted big brake kit.