Are there after market brake modifications for the Subaru? 

The RS2.5 type 4-wheel disk brakes are called 15-inch series by Subaru engineering because they require 15” wheel. At 2800+ lbs these brakes are very well matched to the car. If you have a non-RS car, see the Brake Conversion FAQ to upgrade to this setup. It should be the first serious modification you do to your car, air filter-itis not withstanding. 

The biggest single improvement to these brakes is a set of sticky tires such as Pirelli PZero or Michelin Pilot Sxx “Z”. The next biggest improvement is the addition of STI suspension bushings to keep the control arms and sub-frames from moving around in response to brake and bump loads. Drilled rotors are listed in the “Presents for your car” FAQ, right under air-filters modifications. 

If you regularly melt down your pads, Mintex has a high-temp road compound available. I caution those of you who want to fit true racing pads on the street. These types of pads are of a “get hot, stay hot” composition. When cold their performance is tens of feet off the stock Subaru pads. On that emergency stop from 75mph after cruising on the interstate for the last hour, you want them suckers to work and now. Better to change pads a little more often. 

Available Options: 

The 97 WRX-RA STI ver.IV is using a 298mm (12.9”) SVX rotor casting drilled 5x100mm and 4-pot calipers of as yet unknown origin. I have inspected a pair and they have no casting marks on them. They were a bit “mouse” IMHO.  It uses a special 16x7mm wheel to clear the outside caliper piston housing. It is equipped with standard size, vented disks in the rear. It is possible that at some future date Porsche Brembo 944T adapters will appear for re-drilled SVX rotors. For those of you wanting (hey, we all dream) such a setup it will be less expensive and more effective to purchase the following: 

AP (brake supplier to Prodrive) offers a 335mm rotor, 4-pot caliper kit. It is $2295 list and requires another $1000 in special 6 spoke Speedline 16x7 (16” only at this time) wheels to clear the clear both the large rotor and caliper. 

These brakes are intended certain mountainous regions near Monte Carlo where descending from mountain passes is an art form, and for the German Autobahn where you may need to haul down from 200kph on a regular basis on some remaining no speed limit sections. Their principle advantage over the stock setup is that they can shed much more heat. Under ~70mph there is only slightest advantage. 

For some perspective, I built front and rear sets of 315mm rotors and Brembo Porsche adapters for my Celica GT4 (alltrac) in 1988. At 3200 lbs it had roughly 30% more kinetic energy to handle than an Impreza and 20% smaller front rotors. It desperately needed bigger brakes. Toyota corrected this problem in 1994 by fitting the third generation with this setup. The stock WRX will still out brake an ST205 Celica fitted with these large 315mm brakes. 

I feel in contrast that the stock Impreza 15-inch series brakes are well up to the task of anything but the most insane periods of driving. But, boy did those Brembo’s turn heads. However, other than cruising the boulevard, you really don’t need garbage can lids for brakes on your Impreza. If you have that kind of bread, get a WRX-RA close ratio transmission.