heinzboehmer's 2002 Topaz 6MT Coupe

[bigjae46]

Really? The reason I mentioned CF is because some random website told me epoxy resin was good up to around 300 C. You have more experience with this than me though.

I'm trying to avoid the composite thing because I think it'll be very hard to get right. Hopefully the PET-CF survives.

The carbon will survive but the epoxy is the limitation. There are other processes that can raise the Tg of the epoxy but it would be extremely expensive.

For example… carbon ceramic rotors have no epoxy, made with heat and pressure. Lots of it. There might be an aerospace epoxy but it would also require a lot of heat and pressure.

[heinzboehmer]

I can help you make one sided molds for aluminum or steel ‘stamping’ if that’s where we end up. No problem

Awesome. PET-CF filament is finally back in stock, so I should be able to test it soon

[Bry5on]

I can help you make one sided molds for aluminum or steel ‘stamping’ if that’s where we end up. No problem

[heinzboehmer]

CF will probably do worse than PET-CF unless you use a polyester resin as the matrix instead of epoxy.

Really? The reason I mentioned CF is because some random website told me epoxy resin was good up to around 300 C. You have more experience with this than me though.

I'm trying to avoid the composite thing because I think it'll be very hard to get right. Hopefully the PET-CF survives.

[bigjae46]

Hell yeah. This PT3RS is the only PT Cruiser I've ever driven, so no idea how a stock one drives. But I agree, this thing is way more fun than it has any right to be.



Yeah, it's been pretty fun so far! Prototypes have been ABS, but the duct I'll test with will be PET-CF: https://us.store.bambulab.com/products/pet-cf

Heat deflection temperature of 205 C, so just barely enough based on what I've measured on track. Hoping that the fast moving air helps even further with having it not melt, but we'll see. Worst case, I'll print a mold and make it out of actual CF or stamped aluminum or something.

CF will probably do worse than PET-CF unless you use a polyester resin as the matrix instead of epoxy.

[heinzboehmer]

That's hilarious and awesome lol. We used to have a SRT-4 when I worked at Modified Magazine in a former life. The turbo PT Cruisers have the same engine. Honestly it was way more fun than I thought it could be.

Hell yeah. This PT3RS is the only PT Cruiser I've ever driven, so no idea how a stock one drives. But I agree, this thing is way more fun than it has any right to be.

The ducting is a cool project! what material are you planning on printing the final version out of?

Yeah, it's been pretty fun so far! Prototypes have been ABS, but the duct I'll test with will be PET-CF: https://us.store.bambulab.com/products/pet-cf

Heat deflection temperature of 205 C, so just barely enough based on what I've measured on track. Hoping that the fast moving air helps even further with having it not melt, but we'll see. Worst case, I'll print a mold and make it out of actual CF or stamped aluminum or something.

[karter16]

The ducting is a cool project! what material are you planning on printing the final version out of?

[Nate047]

That's hilarious and awesome lol. We used to have a SRT-4 when I worked at Modified Magazine in a former life. The turbo PT Cruisers have the same engine. Honestly it was way more fun than I thought it could be.

[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.