No offense to anyone offering brake ducting solutions out there - but we thought we could do something better and I'm happy to say I think we achieved it with this prototype setup. This is based on a motorsports design that we have observed on pro cars and then adapted to our RX7's and now to the Plaid.
The plates are made of 1/8" 6061 aluminum, cut to fit the Plaid axles/knuckle. This version is about 80% of the way to good, next rev will have a few more updates to better conform and therefore reduce air leakage. The lip around the edge fits into the MPP 400mm rotors with about 2mm of clearance to seal the back of the rotor. We didn't modify the knuckle - so that meant for the duct entrance we had to do a cutout for the wheel speed sensor and wiring. We've got a couple ideas on how to modify this further so that we can ease the manufacturing and increase the airflow a bit more. This backing plate is sized for a 3" brake duct hose, and while working, we would like to go bigger if possible in a future rev. For comparison the general setup for endurance sports cars is twin 4" hoses!
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For the connection to the nose our friend Damian (a friend by way of our RX7 racing endeavors!) helped us design and print some PC-CF pipes to get from the back of the front duct around the corners to a spot that can be anchored to the horns and then to the 3" hose. This was a ton of fun to model and build but a real challenge too especially with 12+ hour print times! The hose has a built in flange that connects to the front duct sandwiched through the grill. Very solid in the end - and the pipe is held to the car frame with a flexible captured coupling to avoid breaking anything when the bumper flexes a bit. One note - we do not have the air suspension anymore, so we removed the air pump as well. The design we have now wouldn't work with the air pump - something to figure out if we decide to manufacture these for others!
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The final piece of the puzzle was the front duct - from the beginning we had the idea to use the space next to the grill opening - it's just too perfect. Obviously others had the same idea - you can see that in the options that are commercially available now. We wanted to do something that was good enough to look OEM if you didn't know what you were looking at - but the grill and bumper are a very complex shape. In addition we were not willing to run without some sort of screen - we run the car on the street and the track and want to make sure we don't suck a bunch of junk into the duct that block the rotor cooling passages. With some scanning and careful modeling I think we are 95% of the way there. The duct is now a 2 piece part, the main duct is a large area with the screen held in shear on the front via screws to ensure that the screen blockage doesn't limit the airflow through the 3" duct, and then a 3d funnel that matches up with the pipe behind it. There is a cosmetic cap on top of that to hide the screen edge and screws. In order to install it successfully it has captured nuts/threaded rod on the back - there is not a ton of room in there! We've got some ideas on how to improve this design a bit - but in general it works great. We installed it with some 1/16" foam around the edge to ensure we are not damaging the bumper.
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I don't have pictures - but we ran the duct hose like normal, only modifying the fender liner a small amount. We did have to oval the hose as is the case with many cars, and at full lock it can still rub. We are thinking about creating/printing a duct to avoid this as well, but ran out of time for this version and wanted to get some data to prove the value first! The routing is up on top of the sway bar and then under the shock and across to the entrance and it's secured with zip ties and protected with silicone hose.
Here's what the car looked like all ready to run this past weekend. At NCM and Nelson ledges the Motec data appears to show that we achieved the original goal - we are more than 100C down on peak temps (closer to 150C!) The temps decrease more quickly (slope of the cooling curve) and they are not continuing to rise when the power runs out as before. More testing is needed, but we are headed the right direction!
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