[s-cars] G60/brake threads... first-order system factors?

[QSHIPQ at aol.com]

Leigh:

I'm not sure I at all share your love of the 993tt rotor.  First, it's a
pretty well known entity that a cross drilled rotor is NOT a performance
enhancement, it's a vanity one (if you order this option from coleman, they even ask if
it's a street app first = not recommended in a performance environment).
EVEN the 993tt rotor.  Cracks in the holes as you describe them, is a failure of
the component.  "Not that bad?" could be up for debate.  Certainly if you look
to what porsche boys use at the track, it ain't that rotor.

WRT "special" brake ducting...  I find it amazing that just about every WMB
has brake ducts air THRU the subframe to direct cooling air AT the rotors.  Not
just as a bellypan afterthought (audis best effort to date), but in the
unibody design.  I find it somewhat difficult to accept that a rotor is failing,
and you never felt the need.  A rotor's job is to disapate heat, but spinning in
a low pressure zone, it needs some high pressure air, no rotor is good in
radiant heat disapation.

If you want to really learn what a difference ducting makes, buy a 100USD IR
temp zap gun and go to any track event.  I did this a couple years ago, and
it's pretty clear that ducting makes a huge difference in heat disapation.  More
so than ANY crossdrilling could ever achieve.  It's pretty well documented
already, that the 993tt crossdrilled rotor has the same failure issues as every
other one.  Could it be at a higher temp?  Sure, but I sure haven't seen one
on an S car that hasn't achieved that higher temp.

A 993tt rotor is a good rotor, no question.  Is it a "first order" factor?  I
don't believe that for a second.  HEAT is the first order factor.  How you
address it is a first order priority.  Addressing it with a 993tt rotor might be
addressing resistance to heat, all other factors equal.  The problem is still
heat, especially in a non ducted S car.

The type 44 race car I service was having heat related problems with Big
brakes on all 4 wheels.  The customer wanted to go to a huge rotor and bigger
calipers to address the problem. I suggested a more creative and cheaper route,
get high pressure air TO the caliper and rotor.  Cheap and effective.

Want to address miss piggy in battlefield regalia, and not get laughed at?
Do the Brendan Rudack trick...  Haul around some ducting, and zip tie it up
during the track event, and cut it after.  BTWT several times over the years.

Leigh, address the "First Oder" properly, it's heat and heat management.
Regardless of your choice of rotor.


My .02 (cheeseheads are way north of chicago - a fauvre thing)
Scott Justusson
QSHIPQ Performance Tuning

In a message dated 10/28/2003 11:09:47 PM Central Standard Time,
leigha at teleport.com writes:
                             rotors,

and specifically their effective cooling area as a first order factor of
brake 'system' effectiveness.  Now i'm not talking about the heat sink value
of rotors, which is pretty much related to mass, i'm talking about their
ability to dissipate heat to the atmosphere at a high RATE to avoid
pad/fluid meltdown/heat sink soak, ie the ability to track Miss Piggy HARD
in 90 degree ambient and have a rock solid pedal/brake capability after a
spirited half-hour+ track session. (even without special brake ducting;
never felt the need.)

That's why i think the 993tt/UrBR ROTOR is the sometimes overlooked GEM of a
braking system component.  You can put a UrBR caliper on a regular rotor
with plain internal vanes but the cooling rate capability i believe is far
less than the 993tt rotor which is the only rotor I know of that has
vanes-on-vanes-on-vanes.  The radial vanes/inside surfaces, have nubs
sticking out and those nubs have nubs. I have no idea how to quantify the
extra cooling area but it may be as much as ~5X the exposed metal surface,
not counting the area of the cross-holes. There may be some additional
'centrigual fan' effectiveness of such a 'super-vane' design. Even with my
2-ton Miss Piggy, I can be a late-braking fanatic, for as long as the
session runs, even on a hot day (R4 track pads and ATE Super Blue).  All due
to the complete UrBR caliper+ROTOR+trackpad+Dot4fluid 'system'. The UrBR
calipers are great, but put them on plain-vane rotors and i'd guess Miss
Piggy would toast them a _lot hotter.