But don't go out and start dropping racing brake pads into your stock calipers just yet, there's still the coefficient of friction (the Mu symbol in Project Mu) and cold temperature range to worry about. Street pads generally have a lower Mu rating than racing pads, meaning they have less bite and grab, but are easier to modulate and won't eat up rotors as quickly. Racing pads are also not designed to function at as low a temperature range as street pads, because they're designed specifically to help deal with the heat that repeated hard stops on a track will develop. Before racing pads are able to heat up to their operating range, they will chew up brake rotors quickly and actually give worse braking power. This means that if you use racing pads on your mom's Accord, when you first start up the car in the morning and head out, it'll stop worse than stock. Use street pads for the street and race pads for the track. In our case, we didn't want to have to switch pads if we hit the track but we wanted more heat capacity from the pads. We ended up installing a set of Brand X high-performance street pads and gave the system a good bleed. This, along with a good bedding in of the pads, is usually all that's required for most any street car.
Heading back out to Buttonwillow Raceway, we tried it again, this time after changing our brake pads and fluid. First lap, we're warming the car up and crossing our fingers simultaneously. Second lap, still feeling good, braking feel and power is much better than before. Third lap, we haven't had to check for anything inexpensive to hit yet! Fourth lap, is it just us, or are our braking points getting earlier? Fifth lap, back in the same boat.
With performance brake pads, our temperature ceiling is higher, but obviously not high enough. Because this is a dedicated street car, we're not interested in running squealing race pads all the time with big brake ducting running from the front end. So how do we add more heat capacity to Project Two-Face? By using bigger brakes, of course. Big brake kits and upgrades, with their larger brake rotors and calipers, offer many advantages over a stock braking system besides just looks. Fundamentally, a braking system's job is to convert deceleration into heat. Heat that is captured in the rotors, pads, and calipers, and is later cooled by the surrounding air. Do you notice that all we've been talking about so far is the heat capacity of Project Two-Face and not stopping distance? If we really wanted our car to stop shorter, we'd have to upgrade the tires, not the brakes, to something much more hardcore, like Kumho V710 slicks or Nitto NT01's. Because our braking system already has the capacity to lockup our tires, our braking system's bite isn't in question; only by preventing lockup with stickier tires will we stop in a shorter distance. But stopping shorter for one lap is not what we're after, surviving 20 consecutive laps on the racetrack is what we're after.
Simply put, a bigger brake rotor can absorb more heat because more metal equals more material to get hot. For the front of Project Two-Face, we had our eyes set on the 2004 STi Brembo setup. The Brembo calipers are a four-piston fixed caliper design, "fixed" meaning that the entire caliper is rigid and is bolted to the spindle itself, instead of stock where an adaptor is bolted to the spindle and the caliper is bolted on to slide against the adaptor. Featuring more evenly distribued pad wear thanks to the four-piston design, OEM quality dust boots, a vast brake pad selection, the ability to change pads in about thirty seconds, and a direct bolt-on installation to any 2002-2004 Impreza, the STi Brembo was the easiest choice for us. If you install front STi Brembo's on to a 2.0L Impreza, you'll need to get rotors, pads, new banjo bolt washers, and calipers. The stock rubber brake lines and banjo bolts will work, although we recommended aftermarket stainless steel lines, such as Earl's, if you've got the system apart anyways. Technically, the brake lines for a WRX and a STi are slightly different lengths and have different Subaru part numbers, but most aftermarket manufacturers just market one kit for both cars and tell WRX owners to tie everything up and make sure nothing rubs the brake line. Another thing to mention is that the Brembo caliper is really, really big. Wider than the Stoptech, Wilwood, or Brembo Gran Turismo kit, we had to run a 5mm spacer and extended wheel studs in the front in order to clear our +48 offset Work Emotion CR wheels. With 2-3mm between the wheels spokes and the front caliper, it's tight, but Gary Cogis of Race Technologies, LLC (the master distributor for Brembo North America) assured us that clearance is clearance. We have not run into any issues as of this printing.