heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Also, have a plan for the filter.

Looks like I can reposition it so that it will clear the braces and still get somewhat acceptable airflow across it (hopefully).

Here's a view from the back:



Here's how it fits into just the housing:



As you can see, the filter is completely above the fasteners, so that's nice. Means I can keep the locations of those unmodified and then extend a wall up for it to seal against, like so:



Above view also makes it clear that it will interfere with the top locating features on the firewall plug. Those serve to locate both the housing and the filter. I plan to trim them back, so that they don't interfere with the filter, but still serve to locate the housing. I'll add some locating features for the filter to the housing.

You can also see that the filter does not poke through the housing into the engine bay, so no risk of interference with engine bay components. Just need to thin the housing slightly up front.

Since the filter is moving down, the front section will also no longer seal against the cover. My plan is to keep the mounting bosses for that cover where they currently are and just have a wall on the housing that the filter can seal against, like so:



Note that this wall will not extend all the way down to the upper surface of the housing, as that would block all airflow to the filter. I'll add some ribs to make sure the wall doesn't flop around, should be fine. Might also need to add some protrusions to the underside of the cover, so that the filter stays in place.

Now onto airflow.

Unfortunately, I think this change + the clearance needed for the braces will negatively impact airflow across the filter quite a bit, but I don't think there's a good way around that without completely redesigning the housing and potentially using a different filter(s). Regardless, I'll start with this approach and if it really sucks, I'll figure something else out.

Here's a sectioned view to show how much airflow will be affected. Rough eyeball math says that a third or so of the intake area is going to be significantly blocked:



Keep in mind that the space between the braces is essentially useless now. The housing will have to come up to clear the braces (roughly where the pink line is), but I can't just add two notches for each brace, as water would pool in the middle and have nowhere to drain out to. Only saving grace is that the cross section of the big notch will get smaller the closer you move to the firewall, so the blocked filter area is not as much as the above image makes it seem.

Maybe adding a third drain is something I can explore if a bigger redesign is needed?

And lastly, some fit checks against the cowl + a comparison against the stock filter location (in yellow):




These views also show why the filter has to move down. If it doesn't, it'll interfere with the cowl and block the filtered air coming from the front.

So yeah, unfortunately a fairly big compromise in airflow with this bracing. I'll have to see if this design is adequate enough or if I need to figure out a better solution.

[George Hill]

Hard to say for sure overall, but the bolt hole and dowel line up.

[heinzboehmer]

Round 2

Awesome, you test fit the first print just to validate that I didn't get something (e.g. scale) wildly wrong?

[George Hill]

Round 2

[heinzboehmer]

I was referring to varying the thickness of the 3D printed part. I believe the lower half doesn't have any role in supporting the cabin air housing.

Ah gotcha. Redesigning the 3D printed part is a lot of work for not much benefit. Since you can print (mostly) hollow volumes, a thinner part is not necessarily lighter. Also, thinner would lead to higher thermal conductivity.

[bigjae46]

We used cork as core in the Slon version to get the thermal insulation properties back in line with the factory part, for what it’s worth.

The varying thickness of this part makes a normal core material tough if you want to preserve factory fit like Heinz is targeting. You could always print a plastic shell and wrap it in carbon though, which would work. I just don’t see the benefit there though, I think this is actually a pretty good application for a 3D printer vs carbon (and my car has a carbon part here).

I was referring to varying the thickness of the 3D printed part. I believe the lower half doesn't have any role in supporting the cabin air housing. If making a carbon part, you could use a 2mm core in some places and a thicker 3 to 4 mm core in other spots.

Didn't even consider using cork for NVH reduction which I would think would do better than soric. I looked up the coefficient of thermal conductivity, cork is .036 to .065 W/m.K, Soric is .064. So thermal performance should be similar. Actually this is great info that I will eventually need for a different project.

[heinzboehmer]

What is the total volume of the part and how does it compare to the carbon strut mount? You could get a pretty accurate approximation of what the weight would be in carbon. One option is to use a core material which can reduce the weight by up to 33%. Lantor soric is a flexible core material which would work in this application.

Couldn't you make the areas that don't support the cabin filter or seal against the firewall thinner? Use some foam if NHV might be an issue.

Volume is 702.9 cm3, but like Bryson said, there's varying thicknesses everywhere on this piece, so design would need to be modified quite a bit to make it suitable for carbon. Volume of the current design isn't really a good representation of what the volume of a carbon version would be.

Like you mentioned, it can be made a lot thinner, but then you start running into fitment issues. Slon part requires spacers for the fasteners, for instance.

We'll see what happens...

45min down, 17hrs to go, lol

Hell yeah! I'm excited to see how it turns out.

The varying thickness of this part makes a normal core material tough if you want to preserve factory fit like Heinz is targeting.

Yeah factory fit is the big thing. The aftermarket parts I've handled do not fit nearly as nicely as the BMW part does. I'd like to have my version fit as close to factory as possible.

[Bry5on]

What is the total volume of the part and how does it compare to the carbon strut mount? You could get a pretty accurate approximation of what the weight would be in carbon. One option is to use a core material which can reduce the weight by up to 33%. Lantor soric is a flexible core material which would work in this application.

Couldn't you make the areas that don't support the cabin filter or seal against the firewall thinner? Use some foam if NHV might be an issue.

We used cork as core in the Slon version to get the thermal insulation properties back in line with the factory part, for what it’s worth.

The varying thickness of this part makes a normal core material tough if you want to preserve factory fit like Heinz is targeting. You could always print a plastic shell and wrap it in carbon though, which would work. I just don’t see the benefit there though, I think this is actually a pretty good application for a 3D printer vs carbon (and my car has a carbon part here).

[George Hill]

We'll see what happens...

45min down, 17hrs to go, lol

[bigjae46]

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?

What is the total volume of the part and how does it compare to the carbon strut mount? You could get a pretty accurate approximation of what the weight would be in carbon. One option is to use a core material which can reduce the weight by up to 33%. Lantor soric is a flexible core material which would work in this application.

Couldn't you make the areas that don't support the cabin filter or seal against the firewall thinner? Use some foam if NHV might be an issue.

[heinzboehmer]

The air in the print should increase thermal impedance vs stock, yes. But also CF will decrease it, so this is an application where fiberglass filament will beat carbon filament.

For temps I’d probably assume 150C max, which is a 50ish C premium over coolant/head temp to account for heat from the exhaust manifolds from heavy ripping straight to idling and heat soaking. Keep in mind your setup is effectively vented to atmosphere through the hood right now.

Yeah good points all around.

But also, to the carbon point, higher infill means more thermal bridges. Sounds like there's an optimal point somewhere. Might need to do some testing to find it.

[Bry5on]

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.

The air in the print should increase thermal impedance vs stock, yes. But also CF will decrease it, so this is an application where fiberglass filament will beat carbon filament.

For temps I’d probably assume 150C max, which is a 50ish C premium over coolant/head temp to account for heat from the exhaust manifolds from heavy ripping straight to idling and heat soaking. Keep in mind your setup is effectively vented to atmosphere through the hood right now.

[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?