Brake cooling Q's

When ducting air to the brakes, do you want all of the air going to the rotor veins? Is it better/worse to cool the rotor surface as well? Heres where I am as of now:

Going to weld this pipe to the dust cover (cutting the rest of it away), and weld another piece on the inside to direct it to the veins. Heres where my question comes into play- While more than half of the pipe will be directed into the veins, the outer half will be blowing air on the rotor face. Is this acceptable?

Heres the splitter Im working on to put the ducts in. Just a rough cardboard mock-up:

I was thinking of using BMW E30 brake ducts with it (silver piece):

Updated pics:

That looks pretty good. Most of the pipe is pointed at the inner vanes of the rotor. The rotor is an air pump and will actually suck air from your duct out through the edges of the vanes.

The bigger the inlet piece the more pressure you'll get in the pipe at speed.

cooling your brakes will be more effective if you get rid of the dust shields...

rodeck350 said:

That looks pretty good. Most of the pipe is pointed at the inner vanes of the rotor. The rotor is an air pump and will actually suck air from your duct out through the edges of the vanes.

The bigger the inlet piece the more pressure you'll get in the pipe at speed.

Click to expand...

You dont think that the fact that the duct is blowing air onto the rotor face is a problem? A few others say that is a no-no and could warp the rotor. (Id like an explanation for this if there is one, because I dont understand why this would be)
The duct inlet is a tad larger than 3", and the hose is 3" as well.

redvetracr said:

cooling your brakes will be more effective if you get rid of the dust shields...

Click to expand...

Im cutting away whatever isnt needed to hold the duct in place.

I would argue absolutely do not cool only one side of the rotor and rather force it all into the vanes. Because of the expansion rates of hot metal the inner cooled rotor will be ever so slightly smaller than the outer hot rotor face theoretically inducing a cup toward the cool side. I doubt it would be noticable but why do it wrong when it's just as easy to do it right.

Didn't we just have a discussion about the Carroll Smith "_____ To Win" series....

vette427sbc said:

You dont think that the fact that the duct is blowing air onto the rotor face is a problem? A few others say that is a no-no and could warp the rotor.

Click to expand...

GT6Steve said:

I would argue absolutely do not cool only one side of the rotor and rather force it all into the vanes. Because of the expansion rates of hot metal the inner cooled rotor will be ever so slightly smaller than the outer hot rotor face theoretically inducing a cup toward the cool side. I doubt it would be noticable but why do it wrong when it's just as easy to do it right.

Didn't we just have a discussion about the Carroll Smith "_____ To Win" series....

Click to expand...

I wouldn't be that fussy about it. The effect is negligible. This is how all the "old wives tales" get started. After all, you have a dust shield on one side that keeps air from cooling the surface and a huge heat sink bolted to the other. The wheel. That's a huge difference between each side.

You get the rotors real hot then run through a puddle of water and get massive uneven cooling and thermal shock. Then the rotor cracks in half and you crash? Hell no. If rotors were that sensitive to cracking it would be happening a 1000 times a day with all the cars on the road.

relax

rodeck350 said:

I wouldn't be that fussy about it. The effect is negligible. This is how all the "old wives tales" get started. After all, you have a dust shield on one side that keeps air from cooling the surface and a huge heat sink bolted to the other. The wheel. That's a huge difference between each side.

You get the rotors real hot then run through a puddle of water and get massive uneven cooling and thermal shock. Then the rotor cracks in half and you crash? Hell no. If rotors were that sensitive to cracking it would be happening a 1000 times a day with all the cars on the road.

relax

Click to expand...

If I had already welded everything up and put it back together, I would completely agree with you. After all, this is really just a street car that I would like to take to the track when money permits and not have a totally un-prepared car. (Although, with the amount of seat time I have, I think I might have trouble out-driving the stock brakes)


Im with Steve on this one. Its no big deal to oval them now if that is the "correct" way to do it.

GT6Steve said:

I doubt it would be noticable but why do it wrong when it's just as easy to do it right.

Click to expand...

Quick update:
I ovaled the pipe to cool only the vanes and welded it to the dust shield. (still need to clean up my welds and trim the dust shield better)





Going to clearance the pipe-to-rotor a bit more

I would suggest a bead of weld around the opening, it will hold the hose & hose clamp from sliding off....