Essex Competition Brake  System- Front Subaru Impreza WRX STI

In 2001, the bug-eyed Impreza WRX was finally launched in North America, and enthusiasts scrambled to get their hands on the first of Japan's modern rally specials.  Subaru's loyal follwers were rewarded for their patience in 2004, as the heavily reworked 2.5L WRX STI came screaming onto the scene in answer to Mitsubishi's launch of the Evo VIII.

If you're reading this, I don't have to go into too many details about how capable the STI is. At 3300-3400 lbs. these cars are no lightweights. Even more importantly, it's fairly cheap and easy to increase the power to silly levels, and you can cram a decent amount of tire under the fender flares. Uber fast, check...big power, check...meaty tires, check...What does all of that mean?  It's not exactly easy on brakes!

To combat the tortures Subaru expected from its new owners, they equipped the car with a fairly nice brake system from the factory. The STI features 325x30mm brake discs with four piston Brembo calipers up front, and two piston Brembo's in the rear. While it's true that the Brembo system on the STI is far superior to what most production cars come with (particularly in the price range), there are some fundamental differences that set the system apart from a true race-ready system.

Calipers- AP Racing CP8350 Four Piston Forged

Let's first take a look at the calipers. They are the most eye-catching piece of the system, and the one most often touted in marketing material from the manufacturer.  ‘Racing inspired’ is the most common term bandied about, but what does that really mean?  In this case it just means that the caliper is a fixed, opposed piston caliper with a Brembo logo.  Beyond that, there aren’t all that many similarities between the OEM calipers and true Brembo race calipers.  Let’s take a look at some of the OEM design elements.

 Finish

The first obvious weakness when looking at the calipers off of a stock STI is the finish.  OEM Brembo’s always come in a painted finish.  We see this across all of their OEM applications, whether they are red, black, or gold.  OEM's use a painted finish for corrosion resistance and appearance.

Unfortunately, for all of the compliments pretty gold calipers generate, there is an associated price if you drive the car in a track environment.  That price is the chipping, flaking, fading, color shift, and general decimation of the finish in a fairly short period of time.  I’ve seen OEM calipers such as these go from the as-delivered color to a nasty shade of brown in as little as one weekend.  While this is typically worn as a badge of honor among our more hardcore customers, let’s face it…they still look terrible.  More importantly though, all of those bits of paint end up in places they’re not supposed to, which I’ll get to in a minute.

Why does this happen?  Heat.  Paint and powder coat cannot adequately handle the temperatures that calipers hit when run on a track.  Powder coat also has some notorious issues with shrinkage.  The powder coat layer expands and grows when the caliper is heated.  When it cools however, the powder coat doesn’t necessarily shrink in step with the caliper body itself.  What’s left is a loose shell of finish hanging limply on the caliper body.  That shell then cracks and falls to pieces.

Paint can also have similar issues depending on how it is applied.  If you were to line up a few aftermarket calipers from the same manufacturer, you would likely see that the painted finish on each of those calipers is slightly different.  Some have a thicker coat, some thinner, slightly different shades of red, etc.  Painting is to some extent an art form, and must be performed in a tightly controlled environment.  If it isn’t, you’re always going to see variation.  A thick coat makes the part look soft around the edges, and is prone to cracking off in the same manner as the powder coat described above, leaving the underlying finish exposed.  A part without enough paint will look uneven, and will not protect the underlying aluminum particularly well either.

In addition to problems with cracking, flaking, and uneven application, paint and powder coat also experience extreme color shift when heated.  Red becomes maroon or black, gold becomes brown, and black just gets uglier.

Now let’s take a look at some real racing calipers. 

The caliper we are using in the Essex STI Competition Brake System is the AP Racing CP8350.  This caliper was designed to be ultra lightweight, stiff, and durable under all track conditions.  The finish we chose is a hard anodizing.  Hard anodizing is the business under track conditions.

When raw aluminum reacts with the oxygen in the air, a hard surface film develops on aluminum which prevents further degradation.  The process is called oxidation, and you can think of it like rust.  The anodizing process leverages this natural phenomenon, and takes it a step further to produce an extremely hard protective layer of aluminum oxide on the aluminum.  It does so by running an electrical current through an acid bath, and dying it to the desired color.  If you want to know more, Google it.

The result is a finish that is far more appropriate for racetrack use.  Anodizing creates a uniform surface that is much more abrasion resistant than paint or powder coat.  That means if you ding an anodized caliper with a box wrench when bleeding it, a big chunk of the finish isn’t going to chip off into your hand.  While anodized calipers will still exhibit color shift, it will take a lot more heat to get them to change, and they won’t change as dramatically.  They will go from semi-ugly grey, to a semi-ugly grey-brown (see below).  In short, they’ll look like the race calipers they are.  More importantly though, you aren’t going to have bits of anodizing sticking to the sides of your pistons.

Please do keep in mind however, that every yellow AP logo is hand painted on the caliper.  It will degrade over time, particularly if you slop brake fluid all over it.  Our customers asked us for something with at least a little visual punch and some brand recognition, so we had to give them this token.  Also keep in mind that an anodized finish is not designed to be driven through road salt.

Okay, so we’ve established that paint and powder coat are not ideal choices for calipers that will be thrashed at several hundred degrees on the track.  While the finish is the most blatant feature that people key in on, it’s actually not nearly as important as some of the other features in the caliper that allow it to operate efficiently at track temperatures.

   

After the countless times you’ve changed your brake pads, you’re probably never too excited when it comes time to do so.  Changing pads will no longer be a chore with the CP8350.  No more fiddling with a hammer, punch, and pliers, and no tinkering with that annoying spring clip.  AP’s bridge bolt pops out easily with a 5mm hex wrench and a 7mm socket.  It will take you longer to pull off the wheel than it will to change pads.  Less time futzing around in the paddock, and more time driving= fun.

Pistons Sized Specifically for the WRX STI

The piston sizes for our system were specifically chosen to maintain proper brake bias for the WRX STI.  Our front system can be bolted to an otherwise stock brake system with no ill-effects, negative impact on ABS, etc.  The vehicles stock master cylinder can remain, as can the OEM rear brake system.

Compact, Ultra-lightweight Package

Our brake system follows a simple philosophy: Anything larger than necessary to get the job done is simply dead weight to drag around.  One of the major problems with many of the brake packages currently on the market is wheel fitment.  You’re offered gigantic discs and 12 piston calipers, with a pat on the back and a, “Good luck finding wheels to clear those things (insert sinister chuckle here).”  The reality is that many casual racers want to use their OEM wheels on the track, or the smallest, lightest wheel they can find.  Not only is saving unsprung weight critical, R compound tire are much more plentiful and cheaper for smaller wheels.  If the components are designed properly with heavy use in mind, you don’t need to cram boat anchors under your wheels.

Our brake system easily clears the OEM 17” STI wheels, and is actually more compact than the OEM system.  It’s likely that wheels you couldn’t fit over the stock parts may now be an option.  This is a particularly important added bonus for rally enthusiasts considering our system.

If you’re worried about the loss of stiffness due to mass reduction, don’t.  AP’s CP8350 is an extremely stiff, forged design, and the pedal feels rock hard on the STI.

We saved some of the best news about the CP8350 caliper for last.  With pads, it weighs over three pounds less than the OEM caliper!  That’s three lbs. less unsprung weight per corner to drag around.  Also note that most of the weight savings is in the caliper.  As mentioned above, the pads retain nearly the same mass as the OEM shape due to their added thickness.  For the competitive individual, weight savings often becomes the holy grail of modifications.  A lighter car means greater acceleration, superior handling, and less mass to bring to a halt.  At some point reducing weight becomes extremely expensive on a dollar per pound basis.  When viewed in this manner, our system becomes an even greater bargain.

Lifetime Professional Reconditioning Service

Essex is AP Racing's official North American caliper reconditioning center. We have skilled service technicians rebuilding hundreds of AP Racing calipers each year for the top teams in NASCAR Sprint Cup, ALMS, etc.

Hardness testing: After disassembly your calipers will be Rockwell hardness tested against the standard for that particular caliper type as sold new. This test provides a relative understanding of how much fatigue and stiffness loss your calipers have experienced. Tired calipers lead to pad tapering, increased pad wear, leaky seals, and a loss of pedal firmness, all things you want to avoid. Essex will make a replace or rebuild recommendation based on the results of this test.

Ultrasonic cleaning: After passing the hardness test, your calipers will be placed in an ultrasonic cleaner to remove all dirt, debris, brake fluid, etc.  This method produces results that are far superior to what the average racer could accomplish via hand-cleaning.

Inspection and re-assembly: All serviceable parts of the caliper will be inspected and replaced if necessary, including the seals, abutment plates, pistons, and bleed screws.

Cyclical Pressure Testing: After your calipers have been rebuilt, they will be cycled at high and low pressure on a pressure bench to ensure proper functioning. This is important, as certain leaks only show up under specific pressure conditions.

Price: The labor price to rebuild a CP8350 is $78 per caliper.  That does not include parts.  Assuming there has been no damage to the caliper, Essex typically recommends replacing the seals ($40) and bleed screws ($15) during the standard reconditioning process.  For roughly $125, you can have a fresh, professionally serviced caliper in peak operating condition. 

Discs- AP Racing CP3908 Heavy Duty J Hook Racing

There aren’t a lot of positive things to say about the OEM discs on the STI.  They’re ugly, they don’t flow much air, they’re a one-piece design, and they weigh a ton.  Let’s take a look at how AP Racing addresses some of the downfalls of the OEM STI discs.

Two-piece Floating Design with Aluminum Hat

As is the case with most metal, iron brake discs grow substantially when heated.  As it is heated, a disc expands radially, increasing in diameter and circumference.  One-piece disc designs run into problems when this occurs.   Look at the picture below and imagine the disc is being heated on the track.  As the disc expands, the outer edges of the disc are pulling away from the center of the disc, but there are no built-in provisions to allow for that expansion.  The edges of the disc therefore pull, lift, and distort, which is called coning.  Now imagine that disc vertical on the car, running in your caliper.  Coning directly impacts the brake pads’ contact with the disc, leading to uneven wear and tapering, and even a long brake pedal.

Two-piece discs on the other hand, compensate for the expansion of the disc as it heats.  This is accomplished by building ‘float’ into either the disc itself, or the disc hat/bell.  In this case, the float is in the disc.  If you look closely at the picture below, you can see that the mounting holes for the hat attachment bobbins are not round.  They are an oblong shape.  These channels allow the hat mounting hardware to slide as the disc is heated and expands, allowing the disc to run true in the caliper without distortion.  That means less distortion, stress cracks, and pad taper.

If you look closely at the mounting hardware, you’ll notice a few other details that are often overlooked in lesser products.  The

components are specially made for their intended purpose.  These are not cheap bolts found at your local big box store.  They are custom made in the USA for Essex and AP Racing, and they are the exact same components we use on professional racing products.

Floating two-piece discs also have the added benefit of reducing heat conduction to the hubs and bearings, decreasing wear and tear on these costly components.

Please keep in mind that fully floating, two-piece discs do come at a small price.  You will likely notice some rattling and noise from the discs while driving them cold.  The rattling usually diminishes as the discs heat and expands.  On the plus side, you know that you have a true floating disc, and all of the benefits that go with it.  Many competitive products don’t build much, or any, float into their discs, which limits the realized benefits.

The disc hats themselves are manufactured from 2024-T351 heat-treated billet aluminum, with a hard anodized coating.  This material was specifically chosen for its strength at high temperatures, as it will be in direct contact with the searing hot iron discs.  The hats feature scallops on the underside, to allow for heat evacuation along the outer disc face once installed.

 Vane Design

The OEM STI discs use an internal vane design known as a pillar vane, or island vane design.  The primary design objective behind a pillar vane disc is stability and a low production cost.  The discs are not handed or directional.  In other words, the left and right side discs can be swapped on the vehicle.  The reason for this is that the discs are not designed to optimize airflow in any particular direction.  They are inefficient at moving air, and this type of design is also heavy.

Notice the huge difference in size between the inlet ports on the inside of these discs.

The internal vane design on AP’s CP3908 is quite a bit different vs. the OEM discs.  After extensive CFD and thermal stress analysis, AP designed the Heavy Duty J Hook with 70 curved vanes and a wide 16.5mm air gap to increase airspeed and heat transfer, while reducing deflection and remaining reasonably lightweight.  The increased directional vane count on the J Hook Heavy Duty Disc amplifies air speed through the disc, reduces air recirculation between vents, and also increases convective heat transfer and heat distribution.  In other words, both air and heat move more quickly and evenly through the disc, creating increased stability under the extreme loads of racetrack use.  The disc is less prone to coning, distortion, and cracking than the OEM disc, while providing less brake fade, reduced judder, and a longer service life.

Exclusive AP Racing J Hook slot pattern

When you cut a slot or drill a hole in a disc you impact heat transfer. The area around the slot or hole acts as a cool spot when the disc heats up, which is not ideal. Ideally, heat is distributed uniformly around the disc so it can be hit with the cooling air that is pumping through the disc, radiate outwards away from the disc, etc.  Cool spots create stress risers and increase the likelihood of the disc cracking. They also cause the face of the disc to distort unevenly, leading to uneven pad deposits, vibration, and judder.

The OEM STI discs avoid this problem by simply leaving the face blank.  While the risk for NVH goes down, so does the pad bite and feel of the disc through the brake pedal.

During exhaustive R&D testing, AP's J Hook design was found to create a constant pathway of evenly distorted material on the face of the disc.  The hooks are spaced out as evenly as possible both around the circumference of the disc, as well as from the inside edge (where the hat attaches) to outer edge, with a slight overlap to promote even heat distribution/distortion. In addition to reducing cracking, the even heating of the disc also helps provide an even transfer layer of pad material on the disc when you bed them in.

Additionally, the J Hook slot pattern produces a greater number of leading edges for the pads to bite into vs. a traditional curved slot pattern, and particularly a plain-faced disc.  While this may lead to slightly more whirring or scraping noises from the discs when applying the brakes, the benefits of more even heat distribution, less propensity to crack, cleaner pad material transfer during bed-in, and more bite far outweigh the slight increase in NVH for the serious enthusiast.

Feature: Complex metallurgy developed through 50+ years of experience

AP Racing has been designing brake components for more than 50 years.  They've had their components on cars that have won more than 600 grand prix's (Formula 1).  On any given race weekend, AP J Hook discs can be found on 75% or more of the NASCAR Sprint Cup grid.  AP has learned from these experiences, and have developed a proprietary iron alloy with extreme durability, designed specifically for what you intend to do with it (flog the hell out of it).

The primary objectives with OEM discs are simple: they must be cheap and easy to produce.  The design objectives for these two products are vastly different.

Weight

As with the calipers, the discs in our system offer a substantial weight savings over the OEM units.  Despite being 2mm wider, the two-piece AP discs provide a weight reduction of over 4lbs. unsprung weight per corner!

Reasonable replacement cost

Let's face it, no matter how good a brake disc is, it's still a consumable item.  They're no different than brake pads or gasoline.  You beat them up until they crack to pieces, then you throw them away.  If replacement iron is too expensive, you're always driving in fear, waiting to shell out big bucks for a new set.  Despite having the most expansive set of features on the market, the 325x32mm Heavy Duty J Hook's retail for a budget-friendly $249 each.

Going to the track is expensive!   Event entrance fees, hotels, fuel, and tires all add up.  While you obviously want the best product available, you can't afford to pay a small fortune for something you're just going to destroy.  You can buy a cheap set of $150 discs for every event, have relentless heat issues, and find yourself constantly swapping them out.  When you do the math, the long-term value of the AP J Hook's is tough to beat.  You'll enjoy all the benefits without breaking the bank, and you'll spend more time driving and less time wrenching.

Elite level teams choose AP Racing discs because they know the

work has been done to provide the best available product at any price level.  The AP Heavy Duty J Hook is a direct derivative of AP's vast racing experience.  You can buy with confidence knowing that you're getting the best product available at any price point.  A note of caution however: the J Hook design is often imitated, and there are a number of lesser quality imitations on market.  Before purchasing, make sure you are getting an authentic AP Racing J Hook!

Caliper Brackets & Hardware

Caliper brackets for our kit are machined from heat-treated 6061 T6 billet aluminum, and hard anodized, ensuring strength and durability.  All included socket head bolts are a high tensile strength steel.  One of the nice features of our brackets is their cutaway design, which allows for the snug fitment of many currently available brake duct kits.

Brake Ducting

Essex recommends running our system (or any system) with a quality brake duct system.

Spiegler Stainless Steel Brake Lines

For our STI system, Essex is including a pair of the highest quality brake lines currently available.  These lines have a wide range of features not available in competitive offerings.  Below are just a few.  From complete details please visit the Spiegler page on our site.

Economics

From an economics standpoint, the Essex Competition System deserves a seriously hard look if you’re currently thinking about refreshing your OEM setup.  Here are the approximate costs to completely revitalize an OEM STI front brake system, using high quality OEM components:

Powder coat calipers= $100

New Brembo seals & dust boots= $100

New caliper pistons= $200

New brake lines= $85

New discs= $150 (bare bones…plain face, pillar vane…if you want a high-spec disc this number will be higher)

New race pads= $300

Total= $935

That assumes you’re doing all of the labor to disassemble and rebuild everything yourself.  Also don’t forget that this will all take time, which is a valuable commodity to many of us with families, other hobbies, etc.  At the end of the day you’ll still have a used brake system that may have fatigued calipers, heavy components, expensive replacement pads, etc.

The retail price of our system is $2599.  If you pull your OEM front system and sell it to a happy 240sx owner, you’ll likely walk away with $600 in your pocket.  That takes the cost of entry for the AP system down to $2,000.  If you subtract out what it would have cost you to rework your OEM system, that’s roughly an extra $1,000 to step up to the AP Racing setup.

So, for an extra $1,000 over rebuilding your stock parts, you get a completely brand new AP Racing brake system and everything on that rather lengthy list above that goes along with it.  If you go through 5 sets of front brake pads in one season and save an average of $100 per set, that’s $1,000 in pad savings alone over two seasons.

If you instead decide to hang onto your OEM parts when upgrading, you won’t have to worry about losing your shirt when it comes time to part your car and move onto a new project.  Due to their superior quality and storied racing pedigree, AP Racing components are some of the most sought after in the racing world.  While many components fetch only a fraction of their retail price on the used market, AP Racing products retain strong residual value.  That means you won’t be flushing your investment down the drain when moving to your next track toy.

Summary and Conclusion

Based on everything we’ve learned during development, we believe our system offers our customers the following advantages over the OEM STI brake system:  

Finally, keep in mind that we have a whole bunch of very fast corvettes and Evo's around the country now running the exact same caliper and disc setup.  The majority of those cars are 400-550HP and 3,000+ lbs.  Positive feedback from that crowd keeps rolling in.  Additionally, the axial mount version of this setup has been run for years on hundreds of asphalt late models, which are 2800-2900lb., 500hp cars on slicks.

System photos after a tough weekend at VIR

These photos were taken after four drivers spent a day thrashing our system on an '08 STI at Virginia International Raceway.  As you can see, the discs are bed-in nicely, and show no signs of fatigue.  The pads held up tremendously to all of the abuse, showing very little wear.

- The KNS crew, after their first weekend on the track with the Essex Competition System