(Picture shows the 300ZX VENTED rear rotor versus the 240SX SOLID rear rotor. Vented design allows for better heat dissipation than Solid type. Larger rotor allows for better thermal capacity and braking torque.)
Upgrading to Z32 calipers on the rear of your 240SX? Don't use questionable (not to mention rusty) junkyard rotors. These are brand-new Brembo rotors. Zinc-plated to prevent rust and corrosion on the non-swept areas of the rotor. Please specify Slotted or Drilled when ordering.
As quoted from Brembo's website:
"Both drills and slots improve braking consistency, continuously cleaning and refreshing the pad surface. These slots or drilling provide a path to disperse built-up heat and gasses that result from pads acting on the rotors, as well as help to clean and refresh the pad surface.
Both help in interrupting the water film in wet driving conditions, improving the brake response; this effect is more sensitive on cross-drilled discs owing to the different full/empty ratio of the surface and the possibility to have water flowing through the holes in the ventilation gap (on vented discs).
On the other hand, where extreme friction level is required, the adoption of a highly aggressive pad such as in racing applications is necessary and slots are the right solution: being that the slots are not all the way through the disc thickness, the overall mechanical resistance of the disc is higher.
Additionally, all of Brembo’s slotted discs are directional: the discs should be installed such that the end of the slot nearest the outer edge of the disc contacts the pad first."