Found this on a website think some fellas here would be interested.
Introduction
The Mazda 323GTX came with four wheel disk brakes from the factory, but even these can be improved. Many car owners have noticed brake fade or warped rotors after repeated high speed stops. This is do to the small size of the stock rotor and it's inability to dissipate heat. Another problem area that can be corrected with this brake upgrade is the the rotor placement. The stock location puts the rotor behind the hub, making replacing stock rotors an all day event.
A common, and well documented, upgrade for the GTX is to replace the stock rotors with factory rotors from the 1989 Mitsubishi Gallant VR4. This is commonly known as the VR4 Brake Upgrade. This is a simple bolt on upgrade with minor grinding work needed and some unconventional uses of the press. The rotors needed are the 266mm diameter versions. The Gallant also used a 256mm and a 276mm rotor, make sure you get the right rotor.
In order to mount the rotors on the outside of the hubs, the wheel studs also need to be replaced. I am using longer RX-7 wheel studs. The rear wheel studs from the 87-93 Mazda B2200 can also be used.
IMPORTANT! I am told the RX-7 studs do not work on stock wheels, the shoulder is too long, and you will run out of thread when you tighten your lugs.
You will also need to replace the calipers. The swap was first done using front calipers from the 90-94 Familia GTX, sourced from overseas. Since these are not easy to come by, we have determined that the US Protege/Escort GT/MX3 use the same calipers. As it turns out, any bone stock '95+ Ford Escort Wagon or Coupe calipers may be used. Just look for the numbers 22V / 14 stamped on the caliper body. I am using calipers removed from a Ford Escort wagon. Some calipers I was looking to grab were actually stamped 22V / 13. Be sure to look. Your stock brake lines can be modified to work, or you can replace them with Ford units.
The way Mazda should have done it, and the way it should look when you complete the 'VR-4 Brake Upgrade'.
It's easy to see the difference with a side by side comparison. There is a lot more material (and weight) on the VR-4 rotor.
The junkyard calipers after some cleaning and a coat of laquer. The rebuild kits can take some time to order.
The only part that is not a direct bolt on is the rotor. You will need to grind about a 1/4" off the ends of the hub ears. This modification is required to allow the rotor to sit flat on the hub surface. There is a lip on the inside surface of the rotor that you may not notice this if you simply slide the rotor over the hub.
The 'ears' on the stock GTX hubs need to be ground down to fit inside the rotor. A 1/4" is removed from each 'ear'.
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