Heat sinks only work when in direct contact with the heat source they're reducing. The idea is to keep the fluid temperature level to a minimum to prevent boiling, and to keep pad/rotor temperatures low enough that your friction coefficients don't drop below the optimum threshold.

Now, if you have good track pads, you're more than likely going to start boiling the fluid before you exceed the temperature threshold. You could even be solidly in the middle of the "comfort range" for your pads, and still start to boil the fluid.

It's all relative to your system of course, you have to decide where the air will do the most good, because like it or not, heat is dissipated from the caliper.

On various road race cars I've dealt with, we seem to get the greatest benefit by giving the brake assembly as much "head-on" airflow as possible. Vented rotors are going to draw air through them naturally, so getting rid of the dust sheild helps that a lot, but the airflow across everything and hitting the caliper does make a difference. Of course, the better the fluid you use, the less of an issue caliper temperature is as well.

 

They are in direct contact All the heat transfer is through convection.

FWIW, I'm using Carbotech XP8's and Motul fluid, and have no issues with either one - they're fantastic. My dust shields are removed, but I am cracking rotors at a pretty quick rate (I get 2-3 weekends before they crack all the way through). I've been looking into duct options, but its just so hard to fit anything that will pull air to the center of the rotor on these cars.

I dont think the Dali racing ducts as pictured will be able to fit around the hub - with the axle there, there's just not much room. They have a listing on their website for CF ducts for ITR - http://daliracing.com/v666-5/catalog...cfm?focus=1441 - but when I emailed a while ago they said they had supplier issues and had no idea when those would be in.

 

con·vec·tion ( P ) Pronunciation Key (kn-vkshn)
n.
Physics.
Heat transfer in a gas or liquid by the circulation of currents from one region to another.
Fluid motion caused by an external force such as gravity.

Convection doesn't help cool solids as well as it helps to heat the surrounding air, and heat surrounding solids with that heated air.

heat sink
n.
An environment capable of absorbing heat from an object with which it is in thermal contact without a phase change or an appreciable change in temperature.
A protective device that absorbs and dissipates the excess heat generated by a system.

The only other way I can put it is that good brake pads act as a thermal barrier to help prevent heat transfer to the calipers and fluid by having a very aggressive heat gradient from the surface of the pads to the backing plate.

Of course, there really is no viable way to cool the calipers on most cars, so it's largely ignored. Only system I've seen for such an end has been on Semi-truck racers in Britan, where they have a forced water spray on the calipers and rotors.

The main reason I mention this at all is because heat is what allows brake fluid to absorb water faster than nature would, and water is what kills brake fluid effectiveness.

Anyways, I think I've gone on enough of a tangent, since I just had to re-read the initial post to see what the topic was h:

 

Yeah but its all we've got

Thermal contact != physical contact

The amount of energy in the system is going to be the same no matter what equipment you're using if you're driving the same track, in the same car, at the same speeds. The only thing you can do is make sure your equipment can handle it, or slow down

Do performance pads really have lower thermal conductivity than street/OEM pads? I honestly dont know. Its possible that some thermal barrier (backing plate thickness/material) or insulators can slow the rate of conductive heat transfer to the calipers, but I'm not sure how much of a difference that will make, since the heat is still going to get there - if its 6 laps or 3 laps, it doesnt really matter.

That was my point. The caliper is effective at absorbing heat through conduction, and very poor at shedding it through convection, which is the only heat transfer method available.

 

since most calipers have a good surface area (usually pretty rough) why hasn't someone built in a heatsink?...i can only think of wheel clearance or possible distortion in aerodynamics

 

that was my point. Or, rather, physical contact is usually by far the most efficient thermal contact.
The denser the material the harder it is to put heat into it, and the slower it dissipates heat. Track pads are usually quite a bit denser than street pads.