April 2002
964-993
Brake Cooling Duct Upgrade
By Steve Grosekemper
As more and more late model 911's begin to see racetrack duty, it is increasingly apparent that there are significant differences between these cars and the 2,200 pound 911’s of the early seventies. The greatest difference between these cars is not just the horsepower; it's the weight of the vehicle. The newer cars are 30-40% heavier than their earlier counterparts. With up to 100% more horsepower and all this extra weight, the brakes have quite a task ahead of them. A look through the wheel of any newer 911 shows brake rotors and calipers that have become almost gigantic in proportion. Now more horsepower, more weight, and more stopping power means that more heat is generated when you reach the end of a straight and put the binders on. This leads to a very real concern; how do we keep these monster stoppers from overheating?
In our pursuit of increased handling many of us have had our
964’s and 993’s lowered to get the lowest possible center of gravity
and the best cornering ability. While that is all great for vehicle handling,
it does present some problems for brake cooling. The great minds at Porsche
decided to use scoops attached to the top of the front control arms to grab
air from the bottom of the car and direct it to the center of the brake rotors.
It's true that this is a very simple and efficient way to get cooling air
to the front brakes, see figure 1.
Figure 1.
The problems start when we upset the balance of things and lower the front
of the car. It's not uncommon to drop the front of the car down 1½
inches or more from the stock height. While the front bumper goes down, the
air scoop actually goes up and becomes mis-aligned, greatly reducing cooling
airflow to the front brakes.
I noticed this condition of diminishing brake duct efficiency
while I had a very low 993 on my alignment rack. I know that Porsche combated
this same problem on the GT3 996's by adding a metal extension to the bottom
of the plastic scoop. I figured that if it was good enough for a GT3 it is
certainly good enough for me, and decided to use this same concept on the
street cars. The 993 scoops however are not straight like the 996 scoops are.
The idea seemed almost too simple. I'll just attach another scoop to the bottom
of the control arm to aid and extend the original scoop attached to the top
of the control arm. When the two scoops are attached to the control arm, there
is quite a bit of overlapping material. What must be done is to set the scoops
up in a jig simply made out of two 65mm or longer 6mm bolts. Once in the jig,
the scoops can be marked and cut, to be two separate interlocking pieces of
our brake-ducting puzzle, see figure 2.
Figure 2.
The A-arm is 35.4mm thick and this distance must be maintained
when cutting the two pieces in the jig. After each piece has been cut, they
can be re-installed with two new 6mm x 65mm mounting bolts, see figure
3.
Figure 3.
I have only installed these brake ducts on cars with 18-inch wheels, and have had to do some trimming where the wheel hits the scoop when turning. The smaller the wheel diameter, the greater the risk of contact is. The bottom of the scoop may have a tendency to scrape the ground, especially on cars with smaller diameter tires. If this is indeed the case with your car, a small amount can be trimmed off the bottom of the new scoop extension. Our end result will be a new taller brake duct that will restore the original volume of airflow to the front brakes.
The best part of
this whole upgrade is the cost. The plastic 993 brake scoops, part number
993.341.083.00 and 993.341.084.00, only cost $11.38 each. The 964 brake scoops
are virtually identical to the 993 scoops, and their update is the same. The
964 scoops, number 964.341.083.01 and 964.341.085.10, can be had for the same
$11.38 price tag. This is a bargain at twice the price, not something that
can be said for very many Porsche parts these days.
Good Luck!
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