RE: Blau/RPI 4KQ race brake kits?

[Greg Amy <grega@pobox.com>]

Glenn-

I think that main reason that these parts are not considered "street brakes"
is the calipers.

For street applications, you have to be concerned about the longevity of the
system. It would be highly unlikely that a street car would have the brakes
inspected more than once every 2-5 years (or until, "Honey the brakes are
making a grinding noise".) Thus, OEM engineers must design the braking
system with this "lack of attention" in mind.

Drivers of street car are very sensitive to brake noise and "squeal." Brake
"squeal" is caused by the pads rattling around in their mounts. You can't
completely keep the pads completely fixed or bolted in place (otherwise they
won't move down as the pad wears), so designers typically handle this noise
problem by using various springs and clips to "dampen" the rattling and at
least keep the frequency of vibration below an audible level.

For longevity, every street cars has dust boots that go around the caliper
pistons. These boots are there to keep moisture, dust, dirt, grease, oil,
etc  out of the piston bore. If you get the contaminants in there then the
piston bore can rust, get scratched, and even damage the piston bore seal
("o-ring") and piston.

Calipers designed for racing applications are not subjected to the same
design limitations. Racers are expected to rebuild parts weekly, or at least
inspect them after every racing weekend. Therefore the designers can leave
out those parts that are not needed, or that can actually cause failures
(such as the melting of rubber parts due to high temperatures.) Plus, racers
are not concerned about brake noise, simply performance. Hell, even if the
brakes did make noise, some of the NASCAR applications that Wilwood caters
to are so noisy anyway that you wouldn't hear the brakes.

Wilwood calipers are designed solely for racing. Wilwood's engineers never
considered that Audi (and other) fanatics would take their bargain-priced
(yet high racing quality) components and use them on the street. Thus, these
calipers do not have dust boots, nor do they have the ability to use
rattle-reduction clips. They were designed to produce the maximum braking
torque at the expense of all other niceties.

If you use Wilwood calipers, you should expect to rebuild them annually at a
minimum (not expensive, just time-consuming), and expect brake squeal and
rattles. This is not "dangerous", it just requires your additional
maintenance and attention. In return you get a high quality caliper and
low-cost rebuild parts and many, many different choices of pad compounds.
However, it will not be supported by Wilwood, and they are quite adamant
that their parts are for "off-road use only."

Porsche (nee Brembo) calipers are "street" calipers, designed for street
use, and have everything that this moniker implies. Thus, their popularity
for street use.

Greg Amy
Milford, CT


> Someone with BTDT, how well do these Wilwood brake upgrade 
> kits work with
> the stock 4KQ MC?
> 
> Any ideas why they call these 'race brakes' or 'not 
> recommended for street
> use' but they supply street pads with these kits? (just curious)