Brake Ducting

[Ron Earp]

Anyone here have any pictures of brake ducting solutions they've done for GT40s? I was just thinking of various ways to do this similar to our race cars. I was wondering if the side front NACA ducts up top would be at a decent place for intake air, and then route them to hats on the rotors for cooling. Anyone got pictures of their solutions?

Ron

[Ross Nicol]

Ron You may have read my post about cracked rear rotors and fitting new ones.I thought about it for a while and until I can work out a better plan to get up to the Naca ducts on the rear clip, I have run short ducts and taped them to the lower trailing arm to line up with the chassis slot where the arm goes through.I'll post a pic but I still have to host the pic on my own site don't I? I forget how to acheive this often.Ah the benefits of a techno astute son.
With the fronts I intend to run down the footwell rail to the front.

[Fran Hall RCR]

Gents,
my concern would be pulling air into cool the brakes that is "too" cold and can cause rotor degredation and ultimately failure...we saw a rotor failure on our factory C6 Corvette at Sebring last weekend.
If I remember correctly some of the original GT40's pulled air that was preheated from behind the front radiator to lessen the thermal shock to the braking system...

This is more a problem when there are very long straights and then hard braking ,on shorter road courses this should not be such an issue.

My other thought extends to the serious braking forces that we can all now apply with off the shelf monster calipers which may create its own monsters to deal with....hhhmm..drum brakes anyone?? [img]/ubbthreads/images/graemlins/grin.gif[/img]

[Ross Nicol]

Fran During winter we may block ducts to maintain rotor temps but with Australian ambient temperatures ducts are a necessity.I've been racing without any ducts and got away with it until we went to South Australia's Mallala circuit where we ran 10 lap races with 30 degree ambient temps and tight hairpin corners after straights, I boiled fluid in rear brakes and cracked the rotors.Lesson is must have ducts.Always used them on the 240z too.I find once brakes are up to temp long straights only cool a little and temps certainly don't drop to pre race levels.I don't understand your final paragraph except for your drum brake line. My short answer is no thanks.
Ross

[Fran Hall RCR]

Light hearted banter my friend...the forum is having a serious day and I wnated to lighten the tone..

[Ross Nicol]

Fran I enjoy banter, I probably come across a bit serious and don't use LOL or My2c worth enough but I'm tongue in cheek a lot and love a laugh.It's a wonderfull thing to have friends around the world with similar interests and passion.Where I have to draw the line is when I feel I see incorrect information when it relates to something I know about and feel compelled to respond to.I'm hoping to impart my knowledge in a small way but not to offend cause this is not intended.By the way your alloy chassis looks great I'd like to know the all up weight and would you like a car tested down under?
Ross

[Gary Gibbs]

[ QUOTE ]
Gents,
If I remember correctly some of the original GT40's pulled air that was preheated from behind the front radiator to lessen the thermal shock to the braking system...


[/ QUOTE ]
I believe this was the change from Mk IIA vs. Mk IIB where the latter took air from the single nostril just behind the radiator. I believe this was because on the long straight at Le Mans the brakes cooled to much/rapidly. I believe this was discussed in the SAE paper on brake design for the Mk II.

[Ron Earp]

I don't think I'll have too much of this over cooling effect. Heck, ambient temps on race weekends are already hitting 75F and by late May will be 90-95F (35C) routinely in the Southeast where I race. So, for the race cars brake ducting is a must. We also used it in a 13 hour Enduro we ran too, in 50F weather, with no ill effects on the brakes and this was on a long course with not so much braking which should cause more problems with the heat/cool cycles.
I suppose it is more a function of car weight, usage pattern, etc. than anything else.

[Kalun D]

Ron, I suppose it's possible the small NACA ducts could cool the brakes but comparatively speaking they are far less volume than the normal ones on either side of the rad opening.

I'm glad you brought this up as I think it's an important issue. Many are worried about having the largest brakes possible but not worried about keeping them cool.

After you get to a certain size bigger brakes do not yield better stopping because of the tire contact patch limitations. What bigger brakes do yield is better heat resistance. Why can't you improve heat resistance with better cooling, and keep the weight performance edge (rotating, unsprung, overall) of smaller brakes?

This is a fix that's good for anyone on a budget that's not unlimited in that it's achieved with just fiberglass materials and labor as opposed to purchase of expensive larger brakes.

Not arguing that the largest brakes possible don't have their place, just that it may be limited except for the most competitive instances and then only on certain tracks.

I do remember reading that some of the original GT's had issues with overcooling and they ducted through the radiator to moderate temps. It would be interesting to read the SAE article on the subject. It would seem to be an issue of rapid heat cool cycles causing damage but I would think you could adjust it merely by restricting the air intake per conditions.

The ducts I designed use the original intake location. They are glassed to the inside of the front corner light covers (inside fenderwell).

The first pic is of the forms stuck onto sticks preparatory to laying the glass. They are constructed from building insulation styrofoam, covered with foil and waxed with mold release(not enough). This stuff cuts easily with a hack saw blade without the handle and body sanding boards with 36 grit. The hardest part was the round piece, made separately and glued with spray glue to the main body.

[Kalun D]

Here's the pieces while the foam form is being removed. Not sure if it's technically accurate but this is what I call the "lost foam process" in that because of the shape the piece can't be removed without the destruction of the form.

[Kalun D]

Here's the duct pieces bonded to the fender liners. As you can see the wall of the light cover/fenderwell liner piece makes up one side of the duct in that the duct pieces are bonded right to the liner with 2" strips of glass.

[Kalun D]

Here's the light cover/ duct assembly in position inside the fenderwell. (looking at the RF corner from the inside). Everything was done with the strongest weave of conventional glass and strongest conventional resin. 3 layers on the liners(may have been overkill) and 2 layers on the ducts.

The round part of the duct has a 3" diameter and will go to a 3" aircraft type flexible duct. The connection to facilitate the clip movement will be an aluminum flange mounted to the aluminum skin side of the chassis, with the round fiberglass end sealing right on the flange with rubber WS. The flex duct will go from the flange to a similar flange on the brake backing plate.

This design avoids having to make the round section of the glass duct to an exact dimension to fit the flex duct, which would entail more exacting work and straining amatuer skill level.

The "to win" series recommends 3" minimum duct size and the original cars were 4". It's close clearance between the tire at full turn and the chassis side so the original ducts went inside the chassis and back out to clear the tire making it considerably more complex. Since it's doubtful this thing is going to be full out competitively raced it seemed 3" was enough plus it clears the tire.

I'm an amateur glass person so anybody that's a pro and sees something that could have been done easier/better please chime in.

It's actually pretty funny but my first attempt entailed a duct that had the flex hose clamped to the glass duct inside the liner and running all the way to the brakes with no provision for a connection to open the clip! The next day I came out to the shop and looked at it and went DOHHHHH!!!!!

[Gary Gibbs]

Nice job!!! FYI (as previously posted) the SAE papers for the original GT40 and new Ford GT are available as a bound paperback from the SAE and is great reading. Covers a lot of areas that we hit hear on the forum. For example the cooling system of the new GT is analyized in good detail and gives good insight, etc.

[Bill Bayard]

WELL DONE, Kalun!!!! [img]/ubbthreads/images/graemlins/cool.gif[/img]

Did you use a "slip joint" for the duct

to hose connection?

Please post some photos, when you're finished!


Bill

[Ron Earp]

Kalun, I like that idea and the pictures look good, thanks for putting them up. I think I could do something similar when the RF gets here. Robert has those pieces in the nose cut out and they have flanges on the back side so it will be easy for me to graft a "nozzle" on it. I'll probably use high temp hose though like we do on the IT cars and take it over to a hat and backing plate/cover on the rotor that we make. Works very well, sort of looks like the cooling bits on the original cars that directs air all over the disc.R

[Ian Anderson]

Pictures of originals from Le Mans lClassic last year - I cannot find any detail on the rears - but will keep looking
Ian

[Ian Anderson]

second

[Ian Anderson]

Try again

[Ian Anderson]

3rd