heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Can we talk about that PT Cruiser though, how did that thing do

Lol it was there getting a shakedown. Was hilarious to drive. Much more fun than expected.

It's fully racecar'd btw. TC design cage, zero interior anything, bucket, six point harness, fire suppression, etc. Pretty sure that a good part of the reason why it was fun to drive on track was because it's so light. Extremely slow though.

[Nate047]

Can we talk about that PT Cruiser though, how did that thing do

[heinzboehmer]

Friend asked me how the duct mounts to the caliper, so I took some screenshots of the CAD to explain. Figured I'd share here as well for future reference.

Basically, the duct has two tabs that go around that black pad securing pin on the calipers. Problem is that the pad spring clip needs to be compressed for the pin to get installed and then a cotter pin needs to be installed on the pin, so the duct can't be in the way of any of that. To solve this, I made the front tab a separate part. I was originally going to go with a removable top (seen in one of the prototypes above), but the locating features ended up being too small to print reliably. Install process is as follows.

First, the caliper is assembled with just the front mounting tab in place:




Note: this tab also serves to locate the caliper front/rear so that it can't move around and slip off, hence that boxy feature up front.

Then the duct is installed, making sure that the rear tab goes over the rear protruding part of the pad pin:




After that, the duct simply slips over the front tab and gets secured to it with a cotter pin (identical to the one used in the pad pin):



Very easy to install, but we'll have to see how those tabs hold up to vibration and heat cycles. Especially true for the front one, as it needs to be pretty thin to not interfere with the pad when the pistons are fully retracted.

[heinzboehmer]

Track day went awesome. Weather was perfect (cool all day, no rain) and there ended up being a great group of people there. Tons of fun.

M3 friends:




And of course the girodisc dust boots did not survive. Found a melted one on each front caliper:




Also, got my 3D printer and continued with the brake duct development. First prototype on the left and latest on the right:



Test fitted the third one from the left:





Fits great! Newest version has the fan clocked differently for better clearance and has a slightly different front mounting tab design, but is otherwise the same.

Speaking of the fan, I decided that it would be much easier to test the duct performance with one, so I went this route instead of the originally planned passive vacuum generation. I'm still not sure if the fan will live on the duct or if it will live in the belly pan and be connected to the duct with some hose. The fan itself isn't too heavy, but it spins up to 16k rpm, so it puts a decent amount of torque on the duct when the wheel is turned. Having it in the belly pan means I can go to a more powerful fan too if needed. I'll have to do some (destructive) testing and decide if I want to move it or not. More to come

[heinzboehmer]

Love the 3D scanning and CAD work. What program are you using? Maybe I'm thick headed but FreeCAD has not been that easy to understand.

Are you trying to extract air from the brakes? That area is probably high pressure and turbulent. The air coming from the brake ducts comes from a relatively low pressure area which is what makes brake ducts so challenging. People say that to not aim brake duct air to the rotor face, which is correct, but the reasoning of distributing the air through vanes from the hub is part of the reason. The goal is to vent into a low pressure area to encourage air flow, I'd guess that the hub is the lowest pressure area.

You might find that you're not getting enough cooling.

Maybe if you could run that air to a really low pressure area, you could use that duct to extract air and then run a more convention setup to feed air to the brakes.

I used a Revopoint Pop 3 (I think) to scan the car and the Revo Studio software to generate all the meshes and merges. Then imported them all into Onshape and have been using that to design the duct. There's definitely a learning curve to Onshape, but I do like it. Coolest part is that it's cloud based, so I can open up models on my phone, which is really handy when I'm down in the garage.

And yep! Plan is to pull air out through the calipers. I was hoping I'd be able to duct to a low pressure area or build a passive venturi vacuum generator to get the air out. But the more I think about it, the more it seems like I should just make these things active. Stick a fan on the flange and build a small duct to guide the air out of the wheel well nicely. If it's going to be active, then might as well do it properly and add temp sensors and a microcontroller to control fan speed.

This whole idea came to life because the design of the CSL rotors doesn't promote the most airflow from hub to rotor veins. Will likely still install some Bry5on style scoops (will need to adapt his design to my modified dust shield, but that should be simple) to get some extra air to the hub, but this duct I'm designing should help with pad and dust boot temps/life even without those.

[bigjae46]

Love the 3D scanning and CAD work. What program are you using? Maybe I'm thick headed but FreeCAD has not been that easy to understand.

Are you trying to extract air from the brakes? That area is probably high pressure and turbulent. The air coming from the brake ducts comes from a relatively low pressure area which is what makes brake ducts so challenging. People say that to not aim brake duct air to the rotor face, which is correct, but the reasoning of distributing the air through vanes from the hub is part of the reason. The goal is to vent into a low pressure area to encourage air flow, I'd guess that the hub is the lowest pressure area.

You might find that you're not getting enough cooling.

Maybe if you could run that air to a really low pressure area, you could use that duct to extract air and then run a more convention setup to feed air to the brakes.

[heinzboehmer]

Well I completely forgot to account for the weights that come on street pads. Scanned the car with track pads and designed the duct around those. Fortunately the street pads are on the bench, so I just measured them and added to the CAD:


Definitely not going to work with those:



Design needed some tweaking anyway (thinner walls, reworked caliper reliefs), so V2 it is:











Since I'm 3D printing these, my approach is a very software-engineery approach. That is to say I'm tweaking a few things at a time, not validating anything besides a quick eyechrometer clearance check and printing. There's bound to be more iterations of this thing, so I'll just update with a pic of the different versions when I settle on a final one.

[heinzboehmer]

First duct prototype (a.k.a. the vacuum cleaner attachment) done:







I just followed the radius of the caliper, so there should be no clearance issues with the wheel:



Here it is placed into the merged scan:





The merged scan has the wheel at full lock to check clearances. Looks like it will be fine!

Now just need to find some time to print and test.

[bigjae46]

Same connector as for vanos solenoid pack

Thanks! Note to self…don’t plug the auto level harness into the VANOS…🤣

[maupineda]

Same connector as for vanos solenoid pack

[heinzboehmer]

Do you have a part # for that?

I didn't find the connector keyed for that specific location, so I just used the universal one: 61138383300

[bigjae46]

Front xenon leveling sensor connector was crumbling apart and being held on by zip ties, so I changed that out for a new one:

Do you have a part # for that?

[heinzboehmer]

Track day in a week, so prepped the car over the weekend. Swapped pads, swapped wheels/tires and addressed a couple small things as well.

Front xenon leveling sensor connector was crumbling apart and being held on by zip ties, so I changed that out for a new one:




Also swapped out the rest of the dust boots on the front calipers for GiroDisc ones. Not fun to do.

Here's the condition of the Brembo ones that came off:



Three are ripped, but I'm fairly certain that happened when I was removing them. Regardless, they were definitely cooked and very brittle.

All the pistons were still clean though, so not worried about the pressure seals:



Rear Brembo boots looked perfect, so I just left those alone.



I also finally reached out to my friend with the 3D scanner and we scanned the caliper/wheel/wheel well. Scans came out pretty awesome:






Was even able to create a decent merge of all the scans with the scanner software:



Looks like a mess in that pic, but promise the 3D version is totally usable.

Looking forward to finally designing the caliper evacuation duct. Current plan is to have it be two pieces: one that attaches and seals against the caliper and another that will hang out somewhere that sees high velocity air flow. First piece will just serve as an air guide out of the caliper and will connect to the second piece with a short section of brake duct hose. Second piece will be a venturi vacuum generator that will create the necessary low pressure to pull air from the caliper.

I've already started designing some different venturi designs to 3D print and test the effectiveness of. None of my designs are based on any hard science, really. Instead, I plan to use the guess and check method on this . Print a couple different designs, test with a leaf blower, tweak things and keep iterating until I'm happy (or get stuck and have to resort to some actual theory-backed design).

I do also intend to try and see if I can make the final version a one piece thing. Would be a much more elegant solution, but I'm not sure that I can make something that can stick out into fast moving laminar airflow and attach to the top of the caliper and not be gigantic. Plus, the two piece design with definitely simplify testing of the different venturi designs.

Anyway, excited to start messing around with this. I have access to a 3D printer at work, but this project is also making me want to just go out and buy one...

[heinzboehmer]

To get DME data onto the bus, you have to command the k-bus to send it. Same thing testo does, takes control of the k-bus logging.

On my list of things to do is to find/replace everything I can from k-bus to CAN bus, then disable k-bus logging. It’s low on the list though, as I’m pretty sure all of the data I want is not sent over CAN.

Aah that makes sense. Completely forgot that Gauge.S is primarily, well, a gauge

[Bry5on]

Hmm, this is surprising. The k bus is usually decently active, so not sure why those are causing issues. Any idea what the commands being sent out are? Steering wheel button things?

To get DME data onto the bus, you have to command the k-bus to send it. Same thing testo does, takes control of the k-bus logging.

On my list of things to do is to find/replace everything I can from k-bus to CAN bus, then disable k-bus logging. It’s low on the list though, as I’m pretty sure all of the data I want is not sent over CAN.