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AP Racing CP8350 Caliper

Part #: CP8350-24S4L (Right Hand Caliper)

Forged aluminum 4-piston racing caliper, SS pistons & hardware with 4lb. AKB springs, caliper weighs 4.8lbs. without pads

PDF Installation Drawing (223 KB)

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How many features from the best racing calipers in the world can you cram into a $500 caliper? Probably more than you ever thought possible. AP Racing’s CP8350 was designed to be the market leader in performance and features while maintaining a wallet-friendly price point. AP’s newest design brings real racing technology like stainless steel pistons, anti-knockback springs, and integrated hydraulic protection to the average enthusiast at lower prices than the competition charges for watered-down street components. Incredibly, this is achieved while maintaining an unloaded weight of only 4.8 lbs. The CP8350 completely redefines the content/cost ratio among aftermarket brake calipers.

Feature: Commonly available, inexpensive, 20mm thick pad

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The best calipers in the world won't do you much good if you can't find brake pads that fit them.  The CP8350 was purposefully designed around one of the most common pad shapes in the racing world.  Additionally, the pad for this caliper is 20mm thick vs. 12-17mm thick for many competing calipers.

Benefits:

· The CP8350's pad shape is shared across a wide range of calipers from various manufacturers.  That means all of the popular racing pad manufacturers produce pads in this shape, and they're competitively priced.  Pads for some aftermarket calipers can be over $500 per set, which is a hefty sum for consumables that may only last you a weekend or two.  Most of the popular race pads for the CP8350 are under $200 a set.  Do the math.  Five set of pads at $500 = $2500.  Five sets of pads at $175 = $875.  In a matter of months you could pay off your brake system in pad savings alone.  How much will you save over the course of a few years?

· The thickness of a pad helps determine the thermal barrier between the disc face, caliper pistons, and ultimately your brake fluid.  A thicker pad provides greater insulation against fluid fade, which is one of the overarching goals of a big brake kit.  A thicker pad also wears longer all else held equal, meaning fewer required pad replacements and lower running costs.

Race pads for the CP8350 (there are many other brands available, but these are the only ones Essex offers)

 

AP Racing S100 (D41 radial depth)
AP Racing C300 (D41 radial depth)
AP Racing S100 (D50 radial depth)
AP Racing C300 (D50 radial depth)
CL Brakes RC8
CL Brakes RC6
Ferodo DS2500 (D50, tall radial depth for more pad volume)
Ferodo DS3000 (D50, tall radial depth for more pad volume)
Ferodo DS1.11 (D50, tall radial depth for more pad volume)
Ferodo DSUno (D50, tall radial depth for more pad volume)
Ferodo DS2500 (D41 radial depth)
Ferodo DS3000 (D41 radial depth)
Ferodo DS1.11 (D41 radial depth)
Ferodo DSUno (D41 radial depth)
Hawk DTC-05
Hawk DTC-70
Hawk DTC-60
Hawk DTC-30
Hawk HT-10
Hawk HP+
Hawk Black
Hawk MT-4
Hawk HPS

 

Feature: Stainless Steel Pistons

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Some people will argue that aluminum pistons are ideally suited to racing calipers, because the rate of thermal expansion between the aluminum caliper body and the pistons should be the same.  They argue that differing rates of expansion between the caliper body and piston can cause the piston to cock under high heat conditions.  Pure nonsense.   If you look at the most advanced calipers in motorsports today, you'll find that nobody runs aluminum pistons.  F1, NASCAR, ALMS...They all use stainless steel, titanium, ceramic inserts, or other exotic materials that do not have a high thermal conductivity.

Benefits:

Heat reduction is the primary goal of a big brake kit, and stainless steel pistons are far better than aluminum at keeping heat out of your brake fluid, period.  Aluminum has a thermal conductivity that is at least ten times higher than stainless steel.  It more readily transmits heat into your brake fluid, which is exactly what you don't want.  Titanium pistons are a great option, but they are hideously expensive.  Stainless steel offers the greatest balance of heat reduction, weight, and price.  They also alleviate the need for crutch solutions such as fitting a titanium shim between the brake pad and highly conductive aluminum pistons.

Feature: 4lb. Anti-knockback (AKB) Springs

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The term "knockback" or "knockoff" describes when caliper pistons are pushed back into the caliper by the brake disc.  This typically occurs when the driver goes through a series of opposing turns (esses), and is caused by compliance in the vehicle upright and hub assembly.  The brake disc acts as a lever, and forces the pistons back into the caliper body.  When the pistons are pushed back, slack develops in the brake pedal.  An initial press of the pedal is required to bring the pistons and pad back into contact with the disc (taking up the slack) before any actual braking can occur.

To combat this issue, AKB springs are placed behind the caliper pistons.  These springs resist the pressure of the disc against the pistons, and prevent the pistons from being forced back into the caliper.  At the same time, the springs are light enough that they don't cause significant brake drag when combined with the appropriate piston seals.

Benefits:

If you've ever experienced knockback firsthand, it's an extremely disconcerting feeling when entering a corner.  The initial pedal drop you experience can be substantial, and it may feel like brake pressure has been completely lost.  AKB springs can provide a tremendous boost in driver confidence.  You won't need to 'pre-tap' your brakes before each corner, and you'll find the same high, hard pedal waiting for your foot every time.  The more confidence you have, the faster you will drive.

Feature: Integrated bleed screw and crossover tube protection

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How often do you take the wheels on and off of your track car?  At least once per event?  A 30lb. wheel and tire combo can do quite a bit of damage when it collides with a caliper's bleed screw or crossover tube.   Of the hydraulic components shown above, which do you think have better impact protection?

Benefits:

The CP8350's body was designed to protect the bleed screws and crossover piping from heavy-handed crew members and track debris.  These delicate hydraulic components reside in small coves on the caliper body that can withstand the impact of a wheel, tool, rock, etc.  Wheel, pad, and fluid changes become less worrisome and faster, and less time in the pits equals more time on the track.

Feature: Forged aluminum construction

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Forging eliminates porosity and voids, and aligns the molecular structure of the metal in a way that resists deformation.  Forging also allows for greater strength using less material, which means lighter, stiffer calipers. 

Benefits:

· Despite being extremely stiff, the CP8350 weighs in at a feathery 4.8lbs., making it one of the lightest four piston calipers on the market.  Lightweight calipers reduce unsprung weight at each corner, improving your vehicle's handling dynamics.

· Stiffer calipers provide a rock hard pedal feel with easier modulation, less pad taper, improved pad release, and a longer service life.

Feature: Radial Mounting

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Axial mount version at left (CP8250), Radial mount right (CP8350)

Rather than an axial mount, which uses tabs/ears to mount to a specific vehicle's upright, radial mount calipers have two holes that accept custom adaptor brackets.  Radial mounting allows for easy adaptation to a given disc on both the vertical and horizontal planes.

Benefits:

The CP8350 be used on an extremely wide range of production based and purpose built race cars.  Since there are no tabs on the caliper in a fixed orientation, all that is needed is an appropriate vehicle-specific adaptor bracket.  This flexibility allows the caliper to be mounted in leading or trailing positions relative to the brake disc, and on the front or rear of the vehicle.

Feature: Durable hard anodized finish

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Have you ever gotten brake fluid on your calipers when bleeding them?  I thought so.  A painted finish can easily be destroyed by brake fluid.  Painted finishes also tend to have an uneven thickness and texture, and exhibit significant color shift when introduced to heat.  Red turns to maroon then black, and gold becomes a repulsive shade of brown.  Similarly, when powder coated calipers are exposed to the type of heat generated on a racetrack, the powder coat tends to expand and shrink, eventually chipping off or flaking.  Finally, most caliper coatings act as an insulator, locking in the heat you're ideally trying to shed!

Benefits:

A hard anodized finish is much more durable and has substantially less color shift when used on the track.  Anodized calipers start out looking the business, and only look more serious after a good track beating.  If you're desperate for color-matched calipers, pull off the shiny bits and paint them whatever color you'd like prior to installation (most painted calipers are anodized before they're painted anyway).  Just don't cry to us when they look terrible after your first track session.

Feature: Stainless steel abutment plates

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Just about every brake pad comes with a steel backing plate.  Steel is harder than aluminum.  When a hard steel pad backing plate rubs against an aluminum caliper body, it can deform and wear the caliper where the two make contact.  On a quality race caliper, thin metal plates are built into the caliper where the pad meets the caliper body.  As shown at right above, many aftermarket calipers allow the pads to rest on the soft, bare aluminum of the caliper body.

Benefits:

In addition to increasing the durability and service life of the caliper body, having an extremely hard surface for the pads to slide against allows them to move as freely as possible while pressing and releasing the discs.  If the abutment plates do ever wear or become damaged, they're easily removable and inexpensive to replace.  Replacing an entire aluminum caliper due to gouging or damage in this location is neither cheap nor easy!

Feature: Stainless steel mounting boss

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A smooth, stable, and durable interface between the caliper and mounting bracket is ideal for optimum long-term performance.   If the caliper is not seated properly it can shift on the bracket, creating unwanted compliance.

Benefits:

The stainless steel mounting boss provides an incredibly durable interface between the caliper and the mounting bracket.  It ensures years of wear-free performance, even when caliper changes are frequent.  Additionally, if this area of the caliper is ever damaged, the boss insert can be replaced, rather than scrapping the entire caliper. The bare aluminum mounting pads of competing calipers are much more prone to wear, and once they're damaged the caliper is scrap.

Feature: High temperature, low drag seals, with no dust boots

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Not all piston seals are created equal.  The average seal is not designed to withstand the extreme temperatures that a caliper experiences when driven hard on a racetrack.  When exposed to high temperatures they become brittle and fall apart.  That's probably why when you took your car to the track, your OEM calipers wept like your mom did when you left for college.

Additionally, street car calipers typically have a bellows-type dust boot installed in a small groove near the end of each caliper piston.  As the piston extends, the dust boot creates a barrier against debris accumulating on the sides of the pistons (shown below).  While this feature is great for your grocery-getter, it's not very desirable for your track car.

piston_with_dust_boot_200cp8350_competitor_dust_boot_200

(Photo above left by Karateboy88 on Nicoclub.com)

Benefits:

The CP8350's resilient high temperature seals allow the caliper to run longer at elevated temperatures between service intervals.  That means fewer leaky calipers and less frequent rebuilds.  Unless you plan on driving through dirt, debris, or road salt in your track car, dust boots are pointless.  Even if you do plan on driving your car in these environments, dust boots will almost immediately become burned and brittle on the track, and can even create a melted mess on the back of your brake pads.  The remnants of the boots can actually get pulled down into the caliper on the sides of the pistons, potentially damaging your seals.  Friends don't let friends drive track cars with dust boots.

Feature: Simple pad change with one bolt

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Are you tired of taking off your calipers every time you go to the track?  Sick of the little spring clips flying across the garage every time you pull out the pads?  Frustrated with trying to find a good place to rest your caliper while it's still attached to the brake line?

Benefits:

With the CP8350 you only have to remove one simple hex bolt on top of the caliper.  That's it.  Loosen, remove the old pads, and drop in the new ones.  It will take you substantially longer to raise the car and remove the wheels than it will to change your pads.  Swapping pads will no longer be a chore to dread on the Friday night before every event.

Some will argue that without a bridge or cross beam on the caliper, it cannot possibly be stiff.  False.  The caliper's forged construction and careful design ensure an incredibly stiff structure that provides the firmest pedal feel with minimum flex.

Feature: Compact package for wheel fitment

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The CP8350 was purposefully designed with short overhangs and a narrow footprint, while still accepting a 32mm wide disc and 20mm thick pad. 

Benefits:

While 12 piston calipers and 420mm discs have had their day in the sun, most real racers still understand that unused weight at the four corners is...well, dead weight at all four corners!  If you can get the job done with smaller, lighter components, vanity is the only reason not to do so.  A lightweight, compact design allows for a wider range of wheel fitment, while still providing the requisite heat capacity for heavy track use.

Feature: Wide range of differential piston bores

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The CP8350 is available for quantity order with pistons ranging from 25mm to 47mm (1" to 1.875"), in any combination.  Depending on usage and required brake torque, pistons can be either differential bore or four of the same size.

Benefits:

· The extremely wide range of piston bores allows for huge flexibility when applying the CP8350 caliper to a specific platform or application.  The caliper's torque output can be tailored to a target disc diameter or OEM master cylinder size.  That means proper brake bias or balance can be achieved through proper piston sizing.

· Differential bores help eliminate pad taper caused by the accumulation of pad debris at the trailing edge of the pad.  The larger trailing piston creates more pressure at that pad end, and helps keep the pad flat against the disc face.

Feature: Available Long-term Professional Reconditioning

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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 fluild, 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.

CP8350 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.

Benefits:

Rebuilding calipers is a messy affair.  Most racers don't have the appropriate spare parts on hand to properly service a caliper.  They also don't have the proper tools, such as a hardness tester or pressure bench, to ensure that a caliper is operating at its peak potential.  That means they won't know how badly a season of green flag racing has fatigued their calipers, if their calipers are experiencing any pressure drops as a result, etc.

The level of service Essex can provide is far beyond what the average racer can perform in their garage, and our technicians have an immense amount of experience with seriously abused race calipers.  They know what they're looking at, and how to make it right.  You'll have peace of mind knowing that when you put your reconditioned calipers back on the car, that they've been properly serviced and in the best operating condition possible.  You'll also save yourself a lot of time and frustration by allowing Essex to do your dirty work for you.

Feature: AP Racing Heritage, Experience, and R&D

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AP Racing has been supplying the world's finest racing brakes for over 50 years.  Their products have been on the winning cars in more than 600 Grand Prix's, and they continue to be the supplier of choice at the pinnacle of motorsports (Formula One, WRC, ALMS, NASCAR, etc.).  The technology in their products is continually derived from this rich racing heritage, and is embodied across their entire product range.

AP Racing is also an OEM supplier for many of the world's most exclusive and storied racing brands, including Bugatti, Aston Martin, and Lotus.

Benefits:

You can buy with confidence knowing that AP's calipers have been torture-tested at every level of racing, and have passed the stringent regulations required for OEM certification.  The quality of their parts is unsurpassed, and their extensive competition knowledge is distilled in every one of their products.

As you can see, a tremendous amount of thought has gone into the CP8350's design, and it truly embodies AP's slogan, "The Science of Friction."  The robust feature set provides the budget racer with benefits that have previously only been enjoyed at the elite levels of motorsport.  The caliper is saturated with stainless steel hardware for long-term durability, while its modular construction and sensible component selection provide easily sustainable long-term ownership costs.  This all adds up to a caliper that makes it easy to enjoy, easy to maintain, and easy to win.

 

Caliper Type

Two-piece, four piston, forged aluminum alloy

Applications

Road course, time trial, autoX, rally, circle track

Finish

Anodized with painted logo

Piston Type

Stainless steel with 4lb. anti-knockback springs

Standard Piston Size (other sizes available)

Differential bore: 38.1mm x2 & 41.2mm x2

Seals

High temperature, low drag, without dust boots

Hardware

Stainless steel wear plates & mounting bosses

 

Integrated bleed screw and crossover protection

Fitment

Up to 332mm x 32mm disc

Weight

4.8 lbs. unloaded (without pads)

 

 
 
Essex Part #CP8350-24S4L (Right Hand Caliper)
Manufacturer Part #CP8350-24S4L (Right Hand Caliper)

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