Laust Pedersen

I have for some reason battled with overheating brakes when bringing the car to the track and posted about this maybe 8 months ago at which time I was recommended (by Sam Lin?) to improve on my OG-racing “Cool Brake Kit” (944T kit to the right on their web-site contrary to their text) by making a better fit of the air guide to the rotors. Now that I am swapping parts (white to black car) I saw an opportunity to act on this by making a wood mold and buying a $15 fiberglass repair kit.

The picture shows the modified air guides in the left foreground, the wood mold (turned on a CNC lathe) in the front right and the left side old and new front air ducts as well as a connecting air hose.
I deliberately made a slight interference fit so the (rusted part of the) rotor now has ground the fit down to be as tight as possible.

After (painting and) installing it on the left side and left the right side original except for a missing air deflector (no mounting bracket on the strut). In that configuration I did a short test drive with one foot on the brake pedal and a ½ mile slow cool down-drive home. With an IR gun I then measured the max temperatures on the discs (not surprisingly found at the root) and found the max temp of the right rotor to be 113ºC and max temp of the left rotor to be 81ºC . What a difference, so I am happy about this.

While the disc itself is a radial fan, it is apparently quite weak and benefits a lot by sealed ram air to the center section.

If anybody, with the OG-Cool Kit (or a near-term intent to buy one), is interested in the mold please let me know before I throw it out.

Laust

Sam Lin

Nicely done Laust, I told you One thing to watch out for, your resin may not be able to take the heat of track work. Depending what resin you chose for the glassing it can usually only take 400F or so, and 4-digit brake temps that close to the ducts will get them above that. That's the reason most people who do this made theirs out of metal.

Have you replaced your fluid and been bleeding before track events now?

Sam

Claus Groth

Good job. I made the same modification when I built the race car and the epoxy resin has held up just fine with the high temps at the track. I also let the rotor wear the extra fiberglass away for a really good fit.

Laust Pedersen

Thanks guys, in choosing the material the temperature was a concern of mine so it is good to hear that yours (Claus) hold up.

Due to the high thermal conductivity of aluminum, I don’t think that much would be gained by choosing that material (uniform temperature). Making it of metal would still leave the back of the inlet duct to be closed somehow.

Sam, you have a good memory. I did flush my (now diseased) white 951 with ATE-200 fluid and it did help on the dangerously soft pedal (boiling), but the fading was still there. I have no immediate track time scheduled for my black 951, but will do a fluid change before going there and hope that I finally get the brake temperature down in the manageable range. Changing from Design-90 to Twist wheels should help too.

I also had a problem with changed camber after a track event and believe that it had two causes, namely power-coated struts, which provided a slippery clamp to the spindle and the fact that the OG-Racing ducts covers the camber adjustment nut, making it very difficult to get adequate torque (clamping force). I did the obvious, ground off the paint on the mating surface and installed the duct/shield after having set the camber and properly torquing the two bolts. Fortunately I have camber plates to easily switch between daily and track driving.

Here is a picture of the installed duct.

Laust

theedge

Whoa time for a balljoint rebuild there

Laust Pedersen

theedge, so you noticed. I injected some moly-grease there and also have a 968 control arm with a good ball joint and bushing ready, which probably goes in with a set of new motor mounts, which I also need.

Sam Lin

As an aside, how are those struts working for you on the track?

Sam

Laust Pedersen

Sam: “As an aside, how are those struts working for you on the track?”

Oh the struts, they have had a trying life, starting out as standard struts, “upgraded” by Huntley Racing and finally saved by Skip/Paragon with his Koni 8641-1414 Sport installation. The springs are 400# with ride height adjustment (bottomed out at 25.1” fender height) and I have set the Konis to max damping. As such the car behaved real well at the track and immediately drove in the direction I pointed it without wobbling.

I also have height adjustable coil-over 1.5-way adjustable aluminum shocks (from Huntley) set at position 8 of 14 with 500# springs (no torsion bar), but found that configuration too harsh. Sway-bars: 26/18 mm.

The front suspension and sway bars are now on the black car and made a huge difference, so now this car immediately goes where I point it without wobble. Oddly enough the soft stock rear with over-damped Konis works really well, but one of these days I will go through the dreaded task of removing the torsion bars and install the coil-overs, probably with softer springs and at a softer shock setting. Off-line testing of the aluminum rear shocks gave me some confidence in their characteristics and durability (no leaks).

Laust

Claus Groth

<< I also had a problem with changed camber after a track event and believe that it had two causes, namely power-coated struts, which provided a slippery clamp to the spindle and the fact that the OG-Racing ducts covers the camber adjustment nut, making it very difficult to get adequate torque (clamping force). I did the obvious, ground off the paint on the mating surface and installed the duct/shield after having set the camber and properly torquing the two bolts. Fortunately I have camber plates to easily switch between daily and track driving. >>

Laust, I also had camber change due to loosening strut/spindle bolts. Several times! I finally set the camber plates at maximum negative and adjusted the struts to minus 3-1/4 degrees. I then pinned the struts to the spindles with roll pins. That ended that problem.