heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Alright, some data. Car up to temp for a while, couple redline pulls then straight into the garage to measure temps:



It in the 60s today, so I'm guessing the firewall can easily reach 100 C on an actual hot day, once everything is nicely heatsoaked. PET-CF should be fine for this application. If I start seeing warping, it'll be an excellent excuse to try out PPA-CF.

[George Hill]

For reference here is 40%

[heinzboehmer]

Generally the best thermal impedance will come from the smallest air volumes and the lowest gravimetric density you can get away with, so you’re on the right track. I’d probably pick a reasonably high infill personally as the weight penalty isn’t that great. Cubic is a good choice as you definitely want closed cells. You should re-run the Slon test with a desk heater and an IR thermometer!

Hmm, going from 10% to 75% cubic increases weight from 345 g to 746 g.

I know 75% is a lot, but it's right around what looks correct for a moderately closed cell insulator:



Stock is fully solid, so any air volume inside the part (assuming identical exterior dimensions) should increase thermal impedance, no?

[Bry5on]

Yep! That's the plan. I've been doing some research to see what the optimal infill config would be. At first glance, I would think a fairly high infill percentage would work better, as that would minimize convection in the small air pockets. But then you also get more thermal bridging from the infill walls, so would need to do testing to find the optimum balance.

However, I did have a thought this morning. "My" design is a 1:1 copy of the stock piece (i.e. same thickness), so if I print it out of a material with similar thermal conductivity to UP-GF, then any amount of air in the interior should result in a lower thermal conductivity.

Quick (unsubstantiated) search says that UP-GF and PET-CF have similar enough thermal properties, so I'll probably just choose an infill with a non-continuous volume (e.g. cubic) and print it with the lowest infill percentage that still results in a strong and dimensionally accurate part.

Generally the best thermal impedance will come from the smallest air volumes and the lowest gravimetric density you can get away with, so you’re on the right track. I’d probably pick a reasonably high infill personally as the weight penalty isn’t that great. Cubic is a good choice as you definitely want closed cells. You should re-run the Slon test with a desk heater and an IR thermometer!

[heinzboehmer]

Depending on the design, you're also getting infill with a 3DP part. So effectively, some open cell "insulation" is created.

Yep! That's the plan. I've been doing some research to see what the optimal infill config would be. At first glance, I would think a fairly high infill percentage would work better, as that would minimize convection in the small air pockets. But then you also get more thermal bridging from the infill walls, so would need to do testing to find the optimum balance.

However, I did have a thought this morning. "My" design is a 1:1 copy of the stock piece (i.e. same thickness), so if I print it out of a material with similar thermal conductivity to UP-GF, then any amount of air in the interior should result in a lower thermal conductivity.

Quick (unsubstantiated) search says that UP-GF and PET-CF have similar enough thermal properties, so I'll probably just choose an infill with a non-continuous volume (e.g. cubic) and print it with the lowest infill percentage that still results in a strong and dimensionally accurate part.

[discoelk]

Depending on the design, you're also getting infill with a 3DP part. So effectively, some open cell "insulation" is created.

[heinzboehmer]

Love it!

Lol, that seems to be the story for all the doing projects I table on this car

You're making a mold? Have to be careful with any vertical surfaces. That may cause release issues. Need a slight draft angle...maybe 1-2 degrees?

Have to factor in exotherm with the mold. Could see up to 200-300 degrees depending on the exact epoxy you use.

Just gonna print the part, not a mold.

Rough math says that making it out of carbon + cork core will weigh around the same as the printed part, so not even gonna bother trying. The modern printable materials can take heat really well, so I see no downside to printing.

[bigjae46]

Also, this took absolutely forever:

I started with this piece cause it looked simpler than the cabin air filter housing, but, man, was I wrong. Essentially no surface on it is flat, except for the one that butts up against the firewall. Took me a really long time to figure out how to approach all of the curves.

Yes, I realize that a lot of the geometry is there for mold release, but I want to make something that fits all E46s, so I decided to spend the extra time and recreate it as closely as possible. More time spent in CAD land saves me from redesigning the piece down the road if it turns out to not fit on some other chassis configuration.

I also decided to not model the front clip retainer into the piece. I like the idea of using the stock injection molded piece for serviceability. BMW does not sell these separately, so I'm gonna have to go junkyard diving for some. Fortunately, they're just plastic welded in, so they're easy to pop out with a razor blade. This part could also conceivably be recreated, but printing it in a favorable orientation might be tricky.

Also, did some preliminary slicing of the model and the printed version should weigh in at 300-400 g, depending on my choice of material and infill. For comparison, the stock piece weighs in at 1618 g. I do need to split it up into three pieces to fit in my printer, so I'll add some features to bond all of them together nicely. For now, I just added some slicer-generated dowel connectors:

With the stock geometry recreated, I can work on modifying it to accommodate both the braces and the tilted filter. Got some ideas flying around in my mind already for how to approach that. More to come.

Sidenote, since I essentially made a 1:1 replica of the piece, anyone can print it out without modification and save ~1.2 kg. Who's up to be the test fit guinea pig? Hit me up and I'll send you the stl (I'll distribute widely once fitment is validated).

You're making a mold? Have to be careful with any vertical surfaces. That may cause release issues. Need a slight draft angle...maybe 1-2 degrees?

Have to factor in exotherm with the mold. Could see up to 200-300 degrees depending on the exact epoxy you use.

[George Hill]

I started with this piece cause it looked simpler than the cabin air filter housing, but, man, was I wrong.

Love it!

[0-60motorsports]

Thats amazing! I would so buy this from you once its all done.

[heinzboehmer]

Also, this took absolutely forever:




I started with this piece cause it looked simpler than the cabin air filter housing, but, man, was I wrong. Essentially no surface on it is flat, except for the one that butts up against the firewall. Took me a really long time to figure out how to approach all of the curves.

Yes, I realize that a lot of the geometry is there for mold release, but I want to make something that fits all E46s, so I decided to spend the extra time and recreate it as closely as possible. More time spent in CAD land saves me from redesigning the piece down the road if it turns out to not fit on some other chassis configuration.

I also decided to not model the front clip retainer into the piece. I like the idea of using the stock injection molded piece for serviceability. BMW does not sell these separately, so I'm gonna have to go junkyard diving for some. Fortunately, they're just plastic welded in, so they're easy to pop out with a razor blade. This part could also conceivably be recreated, but printing it in a favorable orientation might be tricky.




Also, did some preliminary slicing of the model and the printed version should weigh in at 300-400 g, depending on my choice of material and infill. For comparison, the stock piece weighs in at 1618 g. I do need to split it up into three pieces to fit in my printer, so I'll add some features to bond all of them together nicely. For now, I just added some slicer-generated dowel connectors:



With the stock geometry recreated, I can work on modifying it to accommodate both the braces and the tilted filter. Got some ideas flying around in my mind already for how to approach that. More to come.

Sidenote, since I essentially made a 1:1 replica of the piece, anyone can print it out without modification and save ~1.2 kg. Who's up to be the test fit guinea pig? Hit me up and I'll send you the stl (I'll distribute widely once fitment is validated).

[heinzboehmer]

Nice WORK!

This sounds more and more like a MUST do, IMO you should be damn proud of what you have pulled off.

I am so curious how must of an impact this will have on my convertible.

Appreciate it!

It should still make a difference. Hard to quantify how much, but it'll for sure help with strut tower deflection in a similar way as it does on the coupe.

That's amazing! Great work

Thanks!

Had another friend drive it a few days ago and he was similarly blown away. Hell yeah.

[0-60motorsports]

Did a B-A-B test with a friend today and confirmed that I'm not crazy!

Started with the braces on, drove around the block, removed them, drove around the block, put them back on, drove. He was skeptical that they would make much of a difference, but once the car got up to speed (~30 mph), he immediately noticed a difference. He was kinda blown away by how different the car felt to drive with and without the braces. Felt pretty proud when I saw that reaction

Anyway, firewall plug CAD is almost there. Should be able to start cutting/printing soon.

That's amazing! Great work

[Ramage]

Did a B-A-B test with a friend today and confirmed that I'm not crazy!

Started with the braces on, drove around the block, removed them, drove around the block, put them back on, drove. He was skeptical that they would make much of a difference, but once the car got up to speed (~30 mph), he immediately noticed a difference. He was kinda blown away by how different the car felt to drive with and without the braces. Felt pretty proud when I saw that reaction

Anyway, firewall plug CAD is almost there. Should be able to start cutting/printing soon.

Nice WORK!

This sounds more and more like a MUST do, IMO you should be damn proud of what you have pulled off.

I am so curious how must of an impact this will have on my convertible.

[heinzboehmer]

Did a B-A-B test with a friend today and confirmed that I'm not crazy!

Started with the braces on, drove around the block, removed them, drove around the block, put them back on, drove. He was skeptical that they would make much of a difference, but once the car got up to speed (~30 mph), he immediately noticed a difference. He was kinda blown away by how different the car felt to drive with and without the braces. Felt pretty proud when I saw that reaction

Anyway, firewall plug CAD is almost there. Should be able to start cutting/printing soon.