Porsches have been known for superior braking performance since the 356 C. The 911 has always had a favorable brake swept area-to-weight ratio and the factory’s latest automobiles maintain that tradition. In the tradition of Porsche, it is possible to upgrade any 911/914-6/930/964/993/996/997/Boxster/Cayman to either the latest factory braking system or add an aftermarket brake package that is comparable in performance. Lets talk about things that you need to consider when deciding to upgrade your Porsche’s braking performance.

This section is broken into chapters.

1. General Theory
2. Improved Brake Cooling
3. High-Performance Brake Fluids
4. High-Performance Brake Pads
5. Larger Rotors and Calipers
6. Master Cylinders

The latest street braking systems, the GT-3/GT-2 brakes, are capable ofgenerating 2000+ HP of braking! These brakes are larger than any of the 917 or 935 brakes that were used on cars having up to 4 times more power than the Twin-Turbo 997’s. The limitation is the diameter of your wheels so one must understand that utilizing the larger braking systems requires 17″ or 18″ wheels with the correct offsets to maintain caliper and rotor clearance.
The first thing to discuss is brake fade. There are two main causes of brake fade:

1) Overheated (boiled) brake fluid.
2) Pad material failure.

Brake fluid overheats due to excessive rotor temperature which transfers heat into the pads and
thus the calipers causing the fluid to boil. Overheated brake fluid can change into a compressible
vapor which causes the spongy pedal you feel with hot brakes and this is most prevalent with
fluid that’s been in the system for awhile. The other type of fade is caused by the overheating of
the pad material. When the pad is overheated, the surface of the pad at the rotor contact face
turns to a liquid and lowers the coefficient of friction rather suddenly. This is caused by using the
wrong pad compound for the application (such as street pads on the track) , or not bedding the
pads properly and experiencing the phenomenon known as “green fade”. We will discuss this
when we talk about brake pads.
There are several parts of the overall braking system that can be upgraded individually; other
components require installation as matched parts.
In this order, you should consider:

Brake Cooling

Improving brake cooling should be the first thing you do when deciding to upgrade your brakes to
handle track use and prevent fade. Installing big brakes will do little good unless you remove the
accumulated heat from the rotors and calipers, since adding larger brakes simply builds additional
heat into the vicinity of the brake components as well as the brake hubs and bearing assemblies.
The most effective cooling comes from forcing air into the center of the rotors and through the
vanes. Some cars do not allow this type of cooling and deflectors are installed on the suspension
to direct large volumes of air at the rotors and calipers.
There are several brake cooling kits on the market that work quite well. These inexpensive kits
utilize brake scoops that force ducted air into the eye of the rotor. Certain front spoiler styles
have openings where a creative person could attach cooling hoses that route air to the brakes.
This helps stabilize rotor temperatures and lowers the amount of heat transferred to the pads
and calipers. Consequently, the less heat that is transferred to the fluid, the less chance of brake
fade caused by boiled brake fluid. This will also help maintain the proper working temperature of
the pads. Autocrossers may not need additional brake cooling since that application requires the
brake pads to maintain their temperature for best frictional characteristics. The lower speeds in
autocrossing does not put same demands on the braking system as track events do.

High-Performance Brake Fluids

The next item to upgrade is brake fluid. No matter what brake fluid you use, you need to change
the brake fluid at LEAST every year. We strongly recommend the system is flushed at least once
per year to prevent internal caliper corrosion and remove the old fluid that has absorbed moisture,
thus significantly lowering its boiling point. All non-silicone brake fluids are hygroscopic by nature.
This means that the fluid will slowly absorb moisture over time and the dissolved water in the fluid
boils at 212 deg F, lowering the system’s boiling point drastically. In fact, one to two good hard
stops with old fluid can boil the system instantly, causing the pedal to sink to the floor while you
are trying to get stopped! Brake fluid is relatively inexpensive so change it annually for street use.
Your calipers and its internal parts will last a lot longer if the fluid is kept clean and dry.
Everyone has their favorite method of flushing or bleeding the brakes. We strongly recommend
the pressure bleeding method as the best way to flush the old fluid out and rid the systems of
air bubbles without overstroking the Master Cylinder. We use a pressure bleeder that is portable
for use at the shop or racetrack. This allows one person to flush the brakes and keep the master
cylinder full.
There are several choices for good brake fluid. We have listed the most popular ones and
their physical characteristics as related to braking performance. The most relevant number to
compare is the wet boiling point. This tells you something about the fluid’s affinity for water. The
lower the wet boiling temperature, the more moisture fluid will absorb. True racing-type brake
fluids are quite expensive and frankly unnecessary unless you are must use small brakes such
as in Vintage Racing venues or using carbon-carbon brakes. We list those specifications for
comparison only. Rennsport Systems uses and recommends ATE Super Blue or Type 200 (gold)
for their performance and cost effectiveness.
Lots of people ask about what DOT 3, DOT 4, and DOT 5 really mean. These are a set of
specifications about dry and wet boiling points for each grade of brake fluid. As you will see, this
is a guideline only. You must read the specification on the product’s container. All brake fluid
should be purchased in small cans, and if not used immediately, discarded. Once the seal on the
container is broken, the contents start to absorb moisture.
DOT-3 DOT-4 DOT-5
Dry Boiling Point/deg F 401 446 500
Wet
Now, for comparison, here are the specifications for some of the most popular high-performance
brake fluids in use.

Brake Fluid Boiling Points

Boiling points	Dry	Wet
AP Racing 550	531	261
AP Racing 600	567	378
Castrol SRF	590	518
Motul Racing 600	585	421
ATE Super Blue/200	536	392
Motul RBF 600	594	421

Quite a variation! Before you make any fluid purchases you should know a few things. AP 600 is
not compatible with any other fluid. It was formulated for F1 and other cars using carbon-carbon
brake components that will see temperatures of over 1000 deg/F. Castrol SRF, another very fine
product, will set you back about $ 73 per liter while the Motul and Ate Super Blue brake fluids can
be purchased for about $14 per liter or less. This is why we recommend those two products. They
will perform quite well when changed on a regular basis. Under certain circumstances of track
conditions, vehicle weight, brake swept area, and engine horsepower, one may require the use of
a super-duty fluid such as the Castrol SRF. Be sure that you have effective brake cooling before
resorting to these measures. You should also be sure that the brake fluid that you decide to use
is compatible with what you currently are using. Check with the brake fluid’s manufacturer to be
sure.

High-Performance Brake Pads

This is the next item on the agenda for improved brake performance. There are many choices of
brake pads from very reputable suppliers to choose from. There are many factors that affect the
choice of brake pads that include:

1) Vehicle weight
2) Brake swept area
3) Usage: street, racing, or some of each
4) Personal preference

Since each brake pad compound has an optimal temperature operating range, the factors listed
above will influence the pad operating temperatures. As an extreme example, the old Ferodo
DS11 racing compound didn’t develop much friction until the pads reach close to 450 deg/F . This
made them quite unsuitable for the street, or even cars with large brakes that take some effort to
reach these temps. On a heavy car or one with solid rotors, these pads worked OK, however now
there are excellent performance pads that have good friction characteristics starting as low as
200 deg/F. These items can work just fine on the street as well as the racetrack.
Most performance brake pad manufacturers will provide the working temperatures of their product
range and make ballpark recommendation for each application, that are surprisingly accurate.
Performance-racing brake pads come in several compounds including Ceramic, Carbon-Metallic,
Carbon-Kevlar, Asbestos-Free and other proprietary combinations. All of these have their
strengths and weaknesses such as rotor wear differences, pedal “feel”, and friction-temperature
linearity. A good brake pad vendor should also be able to suggest the right pad for your car based
on what its used for.
Unfortunately for your checking account, these ‘magic’ brake pads are not cheap, however the
performance gains make them quite cost effective due to extended durability. Until these types
of pads became available, owners of early 911’s using “S”, SC, and Carrera sized brakes simply
had to accept the shortcomings of their car’s braking systems unless they could afford to install
Turbo brakes or larger.
Here are some street and racing pads that are currently used:

1) Pagid Racing pads offering 6 compounds for racing and street use. A favorite for Porsches!

2) Performance Friction’s complete line-up for many types of applications

3) Porterfield Racing’s R-4 series of pads

4) Ferodo’s street 2500 and 3500 racing pads

5) Hawk Carbon-Metallic pads

6) Endless racing pads (for GT-3 Cup)

7) Brembo street and race pads

All of these manufacturers make street and race compounds. Some race pads can be used on
the street such as Pagid Orange, Blue & Yellow. Carbon-based performance brake pads do have
some drawbacks that some people may not like. All of these pads will make black dust on the
wheels to varying degrees and they tend to be noisy. Squeaks, screeches and other odd noises
are just part of the package when using these types of pads. Although there is little you can do
about the dust besides not using the brakes, noisy brake pads can be effectively quieted down by
using an anti-vibration shim on the back of the pads as well as chamfering the leading edges of
the pad material. This will go a long way toward minimizing the noise.
To prevent the phenomenon known as “green fade”, all brake pads must be “bedded in” before
you will achieve the maximum friction that your pads are capable of. Green fade occurs when
the binders that hold the pad material become overheated before it has a chance to cure. These
binders and glues that are used to mold the material together gets boiled out and turns to liquid
where the pad meets the rotor surface. This can be a frightening situation since you get very little
warning and the pedal remains firm and high. Bedding the brake pads allows the working surface
of the pad to ‘cure’ so that the boiling out process happens in the first few heating cycles. This
process occurs continuously through the life of the pad, but the effect is most obvious at first and
each brake pad manufacturer has their own specific instructions on how to bed their pads
properly. When you install new pads, you should gently warm the pad up by making 25 to 30
stops, gradually increasing the brake pressure, but never getting them really hot. This takes bit of
practice to perform properly. After making those series of stops, you then make a good hard stop
from 110 or so mph, down to about 30 mph and park the car without holding any pressure on the
pedal. Let the brakes cool enough that the wheels are cool to the touch. At this time, you should
have “cured” the pad material so that it creates its highest coefficient of friction.

Rotors and Calipers

Porsche has used many different combinations and sizes of rotors, calipers, and pads since 1965
on the 911/930/964/993/996/997/Boxster/Cayman series of cars. 996 and later cars received a
one-piece monobloc caliper from Brembo that is less expensive to manufacture than the current
multi-piece caliper and is more rigid than its predecessors.
Porsche has upgraded the rotor and caliper sizes as the weight grew and performance
increased. Rotors from 11.9″ to almost 15″ have been used and calipers from small two-piston
cast iron to massive 6-piston alloy ones have been used on Porsche street and race cars since
the sixties. The 996TT/GT-2/GT-3 and later cars have a optional ceramic rotor package (PCCB)
that is supposed to last for 100K miles. These were found mostly on the 996 Twin-Turbo, 996 GT-
3, 997 Twin-Turbo and 997 GT-3.
Porsche rotor sizes didn’t change much between 1969 and 1989. The Carrera 3.2 models
(’84-’89) had slightly thicker rotors (4mm) than their predecessors. The ‘78-on 930’s used a
derivative of the 917/RSR 4-piston brakes that set the benchmark of performance at that time.
Even today, the 930 Turbo brakes are quite desirable for installation on early, light 911’s using
15″ wheels. The 964-series began the march to ever increasing brake sizes due to increasing
weight and the beginning of the 3.6 litre engines. C4’s from 1989 and C2’s from 1990 to 1994
used larger, thicker rotors than the Carreras. The C2 Turbo cars were the next leap in rotor sizes
that are still in use today on many cars.
Porsche used cross-drilled rotors with mixed success. The Zimmerman rotors used on the 930
Turbo brakes were somewhat soft and crack prone, even though the holes were chamfered.
The later Brembo rotors will also show some wear when used with most performance brake
pads. Some of the best rotors in the world are made in the UK by AP and Alcon. Those rotors,
when properly adapted, are to be superior to the Brembo street ones in terms of wear and crack
resistance. All drilled rotors will crack sooner or later if overheated. Slotted rotors are more
durable in this regard however they are heavier. One reason that most large iron rotors are cross-
drilled is to save some unsprung weight and increase pad “bite”. Since nice big, light, carbon
rotors cost $1000+ each, saving some weight is important. Carbon rotors possess very little
friction until they reach 500-600 degrees F so they are not always the best option. Porsche’s
PCCB ceramic matrix rotors while very light, seem to have mixed success when used for track
events therefore they are oftentimes replace with iron ones for extended longevity and much
reduced operating costs.

Brake Calipers

The first performance brake caliper used on Porsche street cars was the aluminum “S” caliper
beginning in 1969. Prior to that, various iron calipers were used; particularly the “M” and “L”
versions. These “S” calipers were used on all 911S cars, early 2.7 Carreras, and ‘75-‘77 930
Turbos; the latter application with limited success. Those cars have too much power and overall
weight for such little brakes.
The Carrera 3.2 cars used iron calipers (“A” & “M”) in a similar size to the “S” ones. Starting in
1989, the C2/C4 and 993 series were equipped with various sizes of 4 and 2 piston calipers
made by Brembo. This family of calipers were loosely called 928 S-4 brakes due to their
introduction on that car. Offered in many different versions for 944 Turbo, 928S-4, C2/C4 as
well as front and rear versions, these have proven to be the centerpiece of many Porsche Brake
upgrade kits. Various rotors from Alcon, Brembo and Zimmerman allow these to be fitted to
almost any type of 911.
The interchangeability of all of these brake components is one of the great features of a 911. In
most cases, you can adapt the latest Big Red brakes from the 993 TT to almost any 911 if you
use the correct wheels. Of course, you cannot easily adapt the latest Bosch ABS V, however
judicious use of the brake pedal will allow full use of these big brakes.
Here are some rough comparisons between all of these Porsche Brake systems. Due to
variations between caliper piston sizes, and rotor diameters in each application, it’s very hard to
make direct comparisons.
Rotor Sizes F/R Pad area/sq-cm
911T
911S
Carrera
Carrera
911SC
930
Carrera 3.2 84-9 282×24 / 290×24 261
Carrera
Carrera
Carrera
Carrera
C2
C2
993
993
993
993
996 Carrera 318×28 / 299×24 450
996
996
997
Again, use this data only for a rough comparison, not for predicting brake performance. There
are far too many variables to make those projections. Suffice to say, that installing any of the 930
/ 964 / 993 brakes on an earlier lighter car will be an impressive and worthwhile improvement!
There are even larger brakes from Porsche using 380mm rotors that are found on the 993 3.8
RSR, GT-3, Cup cars and RSR racecars.

Master Cylinders

This part of the package is quite easy. Porsche used several sizes of master cylinders from 1969
to the present, ranging from 19mm to 24mm. Brake pedal efforts varied as well from the non-
boosted brakes used on the pre-75 cars to the latest hydraulically boosted Twin Turbo ones.
The main reason to update a Porsche equipped with a 19mm master cylinder is when installing
any of the 4-piston calipers as used on 930’s and the later C2/C4/993 brakes. You must use a
23mm master cylinder to ensure moving enough fluid per stroke into those large volume calipers.
This will prevent the brake pedal from sinking to the floor when actuating these big brakes. The
19mm master cylinder simply doesn’t have the capacity to move enough fluid to move 4-piston
calipers.
Porsches that came with high capacity master cylinders are:
1) Carrera RS’s (Euro) 25.4mm
2) 930 Turbo’s & C2 Turbo’s; ’78-’94 23.1mm
3) All 993-996 25.4mm
4) All 993-996 Twin-Turbo’s 25.4mm
The 89-94 C2/C4′s use a 20.6mm master cylinder If you have excessive brake pedal travel
after installing the Big Red TT brakes, its recommended that you use the larger 23.1mm master
cylinder and vacuum booster from the 993 C2.
As usual, we have just touched upon this subject. There are many good books to read on brakes
and brake system design that will cover this in more detail without being Porsche-specific. If you
are interested, drop us an e-mail and we will make some reading recommendations that are
worthwhile reading.