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For more than a month now I've been patiently gathering materials for my DIY brake ducts project, based on another forum member's trials and results. I figured, since I'm spending $400 on track pads why not spend a little more (plus lots more elbow grease) and put in some brake ducts - it certainly can't hurt.

So what's different between mine and his? Mainly, two things:
- the diameter of the ducts & flanges - he went with 3" and I went with 2.5" for easier routing
- the routing - his come out in the bottom pan (easier install) and mine come out higher through the fender liner (allegedly better flow direction).

Here is my materials list:
4 x 2.5" aluminum flanges
18" x 2.5" reinforced hi-temp silicone hose
4 x 2.5" aircraft quality stainless steel continuous hose clamps
6 x 6mm BMW OEM screws with integrated flanges
6 x OEM BMW threaded clips
6 x nylon screws/nuts license-plate style
1 x discarded piece of fender liner, manufacturer unknown
1 x tube of hi-temp RTV gasket silicone (or any other automotive-rated silicone)
1 x can of Rustoleum Metal primer (flat grey)
1 x can of Rustoleum rubberized underbody black paint/sealant
1 x roll of aluminized thermal wrapping tape

Give or take, around $100 in materials. If anybody else is interested I can post links for easy purchase of some of these specialized materials - the rest can be easily sourced at Home Depot and any local auto parts store.

The main steps involved were:
1. Removing fuzzy material undertray pieces (one big center piece and 2 end pieces).
2. Cutting holes into the main tray, notching the end pieces.
3. Cutting 2 of the aluminum flanges to fit the front of the car and painting them.
4. Hammering the 2 remaining flanges to achieve a curved flange surface.
5. Creating templates for these curved flanges, to aid in fender liner trimming.
6. Trimming the fender liner.
7. Installing the painted flanges at the front.
8. Cutting and Installing the silicone duct to the front and rear flanges.
9. Thermal-wrapping the ends of the oil cooler hoses, wrapping bowden cables in electrical tape.
10. Installing the underbody panel and fastening the fender flanges.
11. Sealing fender flange gaps, if any.
12. Going faster and faster without any brake fade - hopefully.

Here we go...