Essex AP Racing Competition Brake Kit (Front) – CP9668/372mm – ENP Finish – S550/S650 Mustang
AP Racing by Essex Radi-CAL Competition Brake Kit (Front CP9668/372mm) — ENP Finish
The ultimate front brake upgrade for the 2015+ S550 Mustang GT and Mach 1. Featuring AP Racing CP9668 six-piston Radi-CAL calipers in ENP (Electroless Nickel Plated) finish paired with 372x34mm 72-vane J Hook floating racing discs, this kit saves close to 30 lbs of unsprung weight from the front axle versus OEM brakes.
Complete kit includes calipers, discs with 6061 aluminum hats, mounting brackets, Spiegler stainless steel brake lines, and installation instructions. Fits inside OEM 19″ wheels without spacers and many popular 18″ track wheels. Uses standard D54 pads (25mm thick, 54mm depth) — compatible with all major pad manufacturers.
SKU: 13.01.10119-ENP • Application: Track/Competition • Fitment: 2015+ S550 Mustang GT & Mach 1 (excludes GT350/GT500)
AP Racing by Essex
Radi-CAL ENP Competition Brake Kit Front CP9668/372mm — S550 Mustang
The definitive front brake upgrade for the S550 Mustang GT and Mach 1. Six-piston Radi-CAL calipers with 372mm floating discs deliver massive weight savings, superior cooling, and championship-proven stopping power. Fits inside many popular 18″ track wheels and OEM 19″ wheels without a spacer.
Competition Braking
Purpose-Built for the S550 Mustang GT & Mach 1
This kit saves approximately 30 lbs of unsprung weight on the front axle versus the S550 GT Performance Pack OEM brakes. Less unsprung mass means faster suspension response, better mechanical grip, and reduced driver fatigue over long sessions.
The CP9668 six-piston Radi-CAL caliper delivers 50.1 cm² of piston area through graduated pistons (27.0, 31.8, and 36.0mm) for even pad wear and progressive pedal feel. The 372x34mm two-piece floating discs with 72 directional vanes provide cooling capacity far beyond anything the OEM system can deliver.
Fits inside OEM 19″ wheels without a spacer and clears many popular 18″ track wheels. Uses the D54 standard pad shape with cross-references from 18+ manufacturers — you will never be stuck without pads at any track.
Key Advantages
Engineered Without Compromise
Eight reasons this kit dominates S550 track competition
Radi-CAL Design
AP Racing’s patented asymmetric caliper architecture delivers 30%+ greater stiffness than conventional designs while reducing weight and improving airflow around the disc.
ENP Finish
Industrial-grade electroless nickel plating is heat-resistant and extremely hard. Used in hard disk drive manufacturing and military targeting systems. Will not chip, flake, or degrade at track temperatures.
30 lbs Lighter
Saves approximately 30 lbs of unsprung weight on the front axle versus S550 GT Performance Pack OEM. Faster response, better grip, and reduced fatigue on suspension components.
18″ Wheel Compatible
Fits inside many popular 18″ track wheels as well as OEM 19″ wheels without a spacer. No expensive wheel upgrades required — install and go.
72-Vane J Hook Discs
Superior airflow and heat evacuation with 72 directional internal vanes. J Hook slot pattern creates uniform heat distribution with more leading edges for consistent bite.
Stainless Steel Pistons
Ventilated, domed-back stainless steel pistons (not aluminum) provide a superior thermal barrier, keeping heat out of the brake fluid and maintaining firm pedal feel through long sessions.
Universal Pad Shape
D54 standard pad shape is cross-referenced by 18+ manufacturers. Alcon, Brembo, Carbotech, Hawk, Ferodo, PFC, and more — you will never be stuck without pads at any track.
Quick-Change Spring Clip
Included spring clip alternate pad retention system enables faster trackside pad changes. Pop the clip, swap pads, and get back on track in minutes.
Complete Kit
What’s In The Box
-
AP Racing CP9668 Radi-CAL Pro5000R Calipers (Pair)6-piston, 6.9 lbs each (no pads) — ENP finish with ventilated domed-back stainless steel pistons and anti-knockback springs
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AP Racing 372x34mm J Hook Racing Discs (Pair)72 directional vanes — 2-piece fully floating bobbin drive with 6061 hard-anodized aluminum hats and 12-bolt attachment hardware
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Caliper Mounting Brackets & HardwarePrecision-machined brackets with aircraft-quality mounting hardware
-
Spiegler Stainless Steel Brake Lines (Pair)DOT-approved with abrasion-resistant coating and lifetime warranty
-
Detailed Installation InstructionsStep-by-step guide for proper fitment and torque specifications
-
Quick-Change Spring ClipAlternate pad retention system for faster trackside pad changes
-
Not Included: Brake PadsOptional add-on — select your preferred compound at checkout (DS2500, DS1.11, DSUNO, or DS3.12)
-
Not Included: Pad Tension ClipsOptional add-on — billet aluminum blocks with stainless steel springs to eliminate brake noise
Technical Data
Specifications
Caliper (CP9668)
6-Piston Radi-CAL Pro5000R
Disc (372x34mm)
72-Vane J Hook Racing Disc
Engineering
Technology Deep-Dive
Radi-CAL Technology
AP Racing’s patented asymmetric caliper design, developed using advanced CAD and FEA analysis. During braking, massive tangential friction force pulls the caliper in the disc rotation direction (parallelogram effect). The Radi-CAL design distributes body mass diagonally to oppose this force.
The result: 30%+ more stiffness, less weight, better airflow around the disc, and superior packaging compared to conventional symmetric calipers.
ENP Finish
Paint and powder coat degrade under sustained track heat. ENP (Electroless Nickel Plating) is industrial-grade surface protection used in hard disk drive manufacturing and military targeting systems.
Extremely hard with uniform application to complex curves, very low porosity, and easy to clean. Delivers a jewel-like appearance that stays pristine through thousands of track miles.
Stainless Steel Pistons
Ventilated, domed-back stainless steel construction (not aluminum). Stainless steel provides a superior thermal barrier that keeps heat out of the brake fluid, maintaining consistent pedal feel through extended sessions.
The domed back adds structural stiffness under load. Ventilation gaps between pistons promote cooling airflow, further reducing operating temperatures.
Two-Piece Floating Discs
One-piece discs cone when heated unevenly — the center heats faster than the outer edge, causing the disc to warp. Two-piece floating design uses oblong hat mounting holes that allow radial expansion without distortion.
The floating bobbin drive system accommodates thermal growth, reducing stress cracks, pad taper wear, and the vibration that comes from distorted one-piece discs.
J Hook Slot Pattern
Straight slots create localized cool spots and stress risers that can lead to cracking. AP Racing’s J Hook pattern creates a constant pathway of evenly distorted material across the entire disc face.
The result is uniform heat distribution, cleaner pad transfer film, and more leading edges per rotation for consistent bite from the first lap to the last.
72 Directional Vanes
Each 372mm disc contains 72 directional internal vanes that act as a centrifugal pump, drawing cool air through the disc center and expelling hot air at the outer edge. This dramatically increases heat dissipation rate compared to lower-vane-count OEM discs.
At 20.1 lbs per disc versus the OEM’s 34.4 lbs, you get superior cooling capacity at a fraction of the rotating mass — a massive advantage for both braking and acceleration.
How It Compares
Essex/AP Racing vs. OE S550 GT PP / Mach 1
| Specification | Essex CP9668 | OE S550 GT PP / Mach 1 |
|---|---|---|
| Weight (no pads) | 6.9 lbs 32% Lighter | 10.2 lbs |
| Pistons | 6-Piston 3x More | 2-Piston |
| Pad Thickness | 25mm 58% Thicker | 15.8mm |
| Design | Radi-CAL Asymmetric | Conventional |
| Finish | ENP (Electroless Nickel) Track Grade | Paint |
| Specification | Essex/AP Disc | OE S550 GT PP / Mach 1 |
|---|---|---|
| Type | 2-Piece Floating Superior | 1-Piece OEM |
| Weight | 20.1 lbs 42% Lighter | 34.4 lbs |
| Diameter | 372mm | 380mm |
| Thickness | 34mm | 34mm |
| Internal Vanes | 72 Directional 72 Directional | OEM Standard |
| Radial Depth | 54mm | 85mm |
Pad Compatibility
D54 Standard Pad Cross-Reference
This kit uses the D54 standard pad shape — 54mm radial depth, available from 18+ manufacturers worldwide
| Manufacturer | Part Number | 18mm Thick | 25mm Thick | Depth |
|---|---|---|---|---|
| Alcon | PNF4489X532.4 | ✓ | ✓ | 52mm |
| AP Racing | CP3894D54 | ✓ | ✓ | 54mm |
| Brembo | B51 | ✓ | ✓ | 54mm |
| Carbotech | CTP7790A | ✓ | ? | 54mm |
| Circo | MB1658-25 | ✓ | ✓ | 54mm |
| CL | CL5009 | ✓ | ✓ | 54mm |
| Cobalt | AP19 | ✓ | ✓ | — |
| EBC | DP2006 / DP3006C / DP4006 | ✓ | ? | 54mm |
| Endless | RCP086 (D52) | ✓ | ✓ | 52mm |
| Ferodo | FRP3014 | ✓ | ✓ | 54mm |
| Hawk | HB109 | ✓ | ✓ | 54mm |
| Mintex | 1852 | ✓ | ✓ | 51mm |
| Pagid | U1903 | ✓ | ✓ | 54mm |
| PFC | 7790.XX.18 | ✓ | ✓ | 54mm |
| Porterfield | AP7790 | ✓ | ✓ | 54mm |
| Project Mu | F1090 (D52.5) | ✓ | ✓ | 54mm |
| Raybestos | R2600 | ✓ | ✓ | 54mm |
| Wilwood | 8825 | ✓ | ✓ | 51mm |
Fitment
Compatible Vehicles
Wheel Fitment
Confirmed Clearance
Gallery
Product & Install Images
Spare Parts
Replacement Components
Individual replacement parts available for long-term serviceability
Critical Cautions
Pad radial depth: 54mm depth recommended. Pads with 51mm depth will fit but leave an unswept ring on the disc face near the hat, causing a thermal gradient and premature disc cracking under heavy track use.
Pad retention loop: If third-party pads include a pad retention loop, it must be removed before installation to avoid interference with the spring clip retention system.
Brake balance: If upgrading front only, use lower friction rear pads to preserve proper brake balance.
Mounting: Do NOT bolt anything between the caliper bracket and suspension upright. Use only original AP Racing bleed screws.
Pro Tips
Brake fluid: Three 500ml bottles recommended for initial install (full system bleed).
New disc prep: Discs have a rust-prevention coating — wash with soap and water before installation.
Mushy pedal fix: If pedal is mushy after install, cycle ABS via scan tool then re-bleed the system.
Disc sides are handed: Left and right discs cannot be swapped side-to-side. CP7177-350GC is right, CP7177-351GC is left.
Professional Installation
Function Factory Performance offers professional brake service and installation for all AP Racing by Essex brake systems.
Located in Thousand Oaks, California, serving Mustangs, Corvettes, McLarens, and more.
Phone: (805) 206-2523
Lifetime Support
Caliper Reconditioning Program
Built to Last — Backed for Life
Essex is AP Racing’s official North American caliper reconditioning center. When your calipers need servicing after years of hard use, Essex can restore them to factory specification for approximately $155–160 per caliper.
This is not a warranty service — it is a testament to the quality of AP Racing’s manufacturing that calipers can be rebuilt and returned to active competition rather than discarded.
Expert Guidance
Questions About Big Brake Kits?
Our brake specialists can help you choose the right kit and components for your S550 Mustang setup. Give us a call or schedule a consultation.
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