GMG Racing 991 GT3 – Brembo Performance Install & Review
GMG Racing, an Official Brembo dealer, is one of the premier high performance and professional racing shops in Southern California who specialize in Porsche track preparation. GMG Racing’s background in professional racing campaigning multi-car efforts in the Pirelli World Challenge series with both Porsche and Audi FIA GT3 platforms. Using this extensive racing experience accumulated over the years, GMG Racing also offers up the same upgrades supplied by their technical partners that they trust on the racetrack.
James Sofronas, owner driver of GMG Racing, also owns a personal 991 GT3 shop car to showcase GMG’s capabilities on and off the track. One such way is by holding track day and driver training specifically for 991 GT3 owners at The Thermal Club raceway which is very demanding on brakes and tires.
One of the first major upgrades done to the GMG Racing’s 991 “WC-GT3” was improve the braking reliability, longevity, and performance under track use. GMG Racing swapped out the Porsche OE discs, pads and fluid on the 991 GT3 with Brembo 2-piece discs, Race Technologies pads, and Brembo Racing HTC64T fluid.
- Porsche 991 GT3
- GMG Racing
- Brembo 2-piece front disc assemblies.
- Brembo 2-piece rear disc assemblies
- Your choice of front and rear pads although Race Technologies TS20’s were used.
- 6 bottles of Brembo HTC64T Racing brake fluid.
- Tarett Engineering brake caliper studs (*optional, supplied by GMG Racing)
BRAKE DISC COMPARISON
While the 991 GT3 has very sophisticated brakes for an OE brake package, there is always more that can be done with certain components to improve overall longevity and performance. The OE Porsche brake discs, pads and fluid are all engineered with comfort, serviceability and cost effectiveness in mind.
As the braking system’s primary function is to dissipate heat, Brembo uses purpose-designed discs in order to increase the fade resistance and thermal capacity of the system. These discs are directionally ventilated for enhanced cooling and slotted for better performance and continuously refreshing the pad surface. Brembo 2-piece discs are made up of a proprietary advanced cast-iron alloy which offers an exceptional coefficient of friction and resistance to thermal shock and fatigue.
The same Brembo Racing discs trusted every weekend in professional motorsports are also utilized in the Brembo Performance program (GT, GT-R & club race systems).
The OE 991 GT3 co-cast Brembo discs are sized 380 x 34 mm in the front and weigh 24 lbs, and 380 x 30 mm in the rear weighing at 23.4 lbs. The Brembo Racing Heavy Duty “HD” type V front disc assemblies are 24.5 lbs, and the rear Type III assemblies are 22 lbs. The 991 Turbo discs are substantially heavier than the GT3 discs as the Turbo models are harder on front brakes than the GT3 models. Brembo 2-piece disc assemblies on a 991 GT3 or Turbo will offer a net gain in weight savings.
There are many advantages to replacing the OE discs on a Porsche GT3 or Turbo, some of them are:
- OEM Integration: Brembo upgrades are designed to work seamlessly with the OE Master, ABS and existing brake systems (Example: Integration with the rear parking brake)
- Weight Savings: Reducing overall un-sprung weight helps improve vehicle dynamics such as handling, braking, and acceleration.
- Durability: The Brembo discs for these Porsche disc assemblies come from the Brembo Racing program. These discs feature proprietary metallurgy which is resistant to fatigue, cracking, and are engineered for maximum longevity on the street or track.
- Different Slot Types: Extensively used in professional motorsports, Brembo type III and type V disc face types can be used to tune or adjust the brakes’ technical characteristics to the chassis or driver.
- Range: Brembo offers lightweight and heavy duty “HD” disc options to suit the needs of the driver, car model (Turbo or GT3) /setup and environment.
- Replacements: Brembo replacement rings are comparably priced to OE, and when the Brembo discs are worn, only the outer disc ring and hardware needs to be replaced.
- Drivability: Brembo 2-piece discs maintain the drivability of the OE brakes by using anti-rattle hardware. Brembo’s specific anti-rattle disc hardware utilizes a spring fastener in order to slightly preload the assembly which eliminates the noise (clattering) generally associated with floating discs.
NOTE: Brembo’s specific anti-rattle hardware which is commonly used in high performance brake disc assemblies was actually developed in the 1990s. This innovation was initially engineered exclusively for the McLaren F1 supercar which is why the hardware is often nicknamed the “McLaren” spring.
BRAKE DISC INSTALLATION
GMG technicians Ruben and Sergei (who drives a 997 Turbo himself) used their extensive Porsche know how to install the Brembo 2 piece disc assemblies on the GMG 991 GT3 shop car.
FRONT DISC ASSEMBLIES
The OE front discs were the first to be installed. The Brembo performance 2-piece discs and Race Technologies pads are a direct replacement to the OE units. GMG made sure to push the pistons all the way back in to ensure proper stack width (2 pads and brake rotor total width). The Porsche center lock “lug” was then removed and the Brembo 2-piece disc assembly and pads were then installed. Once the Brembo performance disc assemblies were fitted, the OE Caliper was re-installed using brand new caliper studs. The entire process was done on the front right disc, and then the front left disc.
The Race Technologies TS20 compound was specified as the baseline pad since the car will be street driven and used on the track. The TS20 offers low noise, dust and good pedal feel. It is also an excellent dual purpose compound for street and light track use.
Since the GMG Shop car is also their test car, the car will see extended track time on many southern California circuits. A Brembo Type V 380 x 34 mm front disc was specified for the lowest disc and pad wear under heavy track conditions. An optional Race Technologies endurance compound was also supplied for dedicated track use.
- Brembo Type V (endurance face type): motorsport developed face type with marginally less initial response compared to the type III face type. The Brembo Racing type V face type was also designed to have lower pad and disc wear for certain long distance endurance races (mostly 10, 12 and 24 hour races).
REAR DISC ASSEMBLIES
Once the front disc assemblies were installed, GMG then turned their attention to the rear discs and pads. The exact same installation procedure was followed for the rear disc assemblies as well. The rear right corner was installed first, and then the rear left corner was installed. GMG installed new caliper studs on the rear as well when re-installing the OE Porsche calipers. Race Technologies TS20 compound pads were used for the rears as the baseline pad.
The Brembo Type III 380 x 30 mm rear brake disc was specified for optimum balance and brake release under heavy track conditions. This is because the 991 GT3 shifts its’ brake balance towards the rear under braking. The smooth release characteristics of the Brembo Type III face type can help a driver avoid rear tire in stop lock up while still maintaining optimum braking performance.
- Brembo Type III (aggressive face type): motorsport developed face type with an emphasis on high initial response while maintaining a smooth pedal release.
As mentioned earlier in this article, the Brembo 2-piece disc assemblies are compatible with the Porsche factory parking brake. One does not have to compromise and lose the parking brake functionality when installing the Brembo disc assemblies.
BRAKE FLUID AND BLEED
Upgrading brake fluid for spirited, track or racing use is easily one of the most overlooked things when thinking of upgrading any component or part of the brake system. Brembo’s HTC64T brake fluid is the top fluid used in the top professional racing categories around the world (Examples: F1, FIA GT, LMP1). This is because the Brembo fluid offers low compressibility, good after boil recovery, and high boiling points.
- Brembo HTC64T Typical Applications: Open Wheel*, Stock Car, Rally, Endurance & Sprint GT**, Track Day.
*Brembo HTC64T is one of a very few select fluids being actively used by F1 teams.
**Brembo HTC64T and LCF600 Plus are both racing brake fluids which are actively used and homologated for FIA GT3 & GTE based sports-car racing.
- Independently proven low Compressibility at severe temperatures.
- Dry Boiling Point: 335 C (635 F)
- Racing Use Only
Brake fluid performs a very critical function as it is the “life blood” of the brake system, as it is the foundation to hydraulically transfer brake pedal effort to the brake caliper’s pistons. Brake fluid also performs a vital function of lubricating caliper piston seals brake fluid performance (or the lack of) can directly affect brake pedal feel, pressure and consistency through the operating temperature range. It is also one the most cost effective ways to improve brake pedal consistency (avoiding spongy pedal) under high temperature use.
Once the Brembo performance 2-piece disc assemblies and RT pads were installed on all four corners, the OEM brake fluid was flushed and bled with Brembo Racing HTC64T brake fluid. As the fluid was being bled on each corner, GMG made sure to keep an ample amount of new fluid filled in the master cylinder reservoir to ensure that air did not enter into the hydraulic system.
ON TRACK IMPRESSIONS
To evaluate the results of the new Brembo discs, fluid bleed, and RT pads, the GMG Team took the 991 GT3 shop car to Thermal Club.
Driver (James Sofronas) and GMG Team comments: Testing out a new setup @thethermalclub today! @jamessofronas had the GMG 991 GT3 out and with the new Brembo Brake pad and Rotor setup says that the car is even more amazing! A predictable pedal feel without activating the ABS too early. A must have for any car that is going to see some track time! Combined with Pirelli Trofeo R tires it is just a winning combo!
Thermal Club located in Palm Springs, California often has very high ambient temperatures which can be demanding on the car, tires, and brakes. The effectiveness of brake cooling is only as good as the temperature of the air flowing thru the brake ducts (if the ambient air is hotter, the brakes will not cool down as much). The track layout and surface can be very similar to some of the European GT tracks, featuring many high speed to low speed braking zones, and a high level of mechanical grip (the more grip you have, the harder you can brake). GMG Racing has setup their shop GT3 understanding the demands of the various tracks around Southern California, and the Porsche 991 GT3, for optimal results.
Modern sports cars have very sophisticated OE ABS systems and engaging the ABS under braking can lead to poor threshold braking, lack of pedal feel, and potentially result in a slower lap time. Having a high overall level of braking confidence and control, usually allows the driver to spend less time on the brake pedal. If the brakes offer enough performance and control for the driver to stay out of ABS engagement (depending on their driving style and car setup), the result is usually a faster lap time on track.