Interest check: custom CNC brake duct backing plates for E36/E46. Need 20 people committed to get unit price under $150. Anyone in?

Let's be honest: if you track your E36 or E46, you've probably fried a set of pads, boiled fluid, or cooked a wheel bearing. Brake cooling isn't optional once you're running real track pads and pushing the car. The problem is that proper backing plates — the ones that actually route air into the center of the rotor instead of just pointing a hose vaguely at the hub — cost a fortune.

I've been looking at options for my E36 track car. GruvenParts sells a set for $109.99, which is affordable, but their design intentionally blocks off half the inlet to prevent "abrupt cooling" of the rotor surface — I'd rather have full flow and manage temps with driving technique. The AAF kits from Turner run $155–341 depending on options-. Hard Motorsport's aluminum backing plates are solid but you're paying premium pricing for the brand. And if you want carbon? $300–400.

So I started talking to a local CNC shop about doing a small production run of our own design.

The Design

We're CAD-modeling a plate that:

• Fits behind the wheel bearing hub without requiring hub removal (install by cutting the factory dust shield)

• Routes 3" hose directly into the rotor hat area — air goes into the center of the rotor and exits through the vanes, which is where it actually does cooling work

• CNC machined from aluminum (aiming for 9–10 oz per plate — about half the weight of steel options)

• Features an inner flange that fits inside the rotor face to direct more air into the rotor vanes

• Powder-coated satin black for corrosion resistance-

• Uses factory mounting locations with stock hardware

The shop has already cut a prototype on their water jet and the fitment looks promising. The duct hole is as large as we can make it without hitting the cast upright or requiring expensive forming of the tube. The tube angle is designed to clear the upright, strut, and clears a 9" wheel.

Compatibility

• E36 — M3 and non-M (328, 325, etc.)

• E46 — M3 and non-M

• Fits stock rotor sizes; BBK compatibility can be discussed if there's enough interest

• Accepts standard 3" brake duct hose

Pricing

Here's the breakdown the shop gave me:

So the magic number is 20 commitments to get under $150 a pair. That includes:

• CNC-machined aluminum plates (pair)

• Powder coating

• All mounting hardware

• Shipping to continental US (international at cost)

Timeline

• Interest check: now through end of July

• If we hit 20 commits: shop starts production mid-August

• Estimated delivery: 4–6 weeks from production start

What I need from you

If you're interested, reply with:

1. Chassis (E36 or E46)

2. M3 or non-M

3. Rotor size (stock or BBK — if BBK, please specify)

4. Quantity (1 pair or more)

Discussion points

• Would you prefer raw aluminum (uncoated) to save a few bucks, or is powder coat a must?

• Any interest in also sourcing the 3" SCAT / silicone hose as an add-on? I can probably negotiate a bulk rate.

• Anyone have feedback on specific clearance issues with aftermarket control arms or bigger wheels? I want to make sure the design works for the widest range of setups.

Why not just buy from Gruven or Turner?

Gruven's price is good at $109.99, but their design intentionally blocks half the inlet. I want full-flow. Turner/AAF kits are $155+-, Hard Motorsport plates are well-made but priced at a premium. And a used set on Bimmerforums recently sold for $120 shipped, so there's clearly demand for affordable aluminum plates. I'm trying to split the difference — better design than Gruven, better price than Turner.

A note on the "why"

If you've ever had brake fade in a long session, you know the feeling: pedal goes long, you start braking earlier, your confidence evaporates, and your lap times go to hell. Brake cooling is one of those upgrades that doesn't make you faster on paper — but it keeps you fast lap after lap. It protects your pads, your fluid, your wheel bearings, and your ball joints from heat damage. For a track car, it's not a luxury. It's maintenance.

Let's make this happen

I'm not a vendor. I'm just a guy with a track car who wants good parts at a fair price. If we get 20 people on board, this run happens. If not, I'll probably still get a set made for myself and a few friends — but the price will hurt.