heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Speaking of packaging, I scanned the engine bay with the braces installed and then individually scanned the firewall plug, the cabin air filter housing and the cable tray. Here's how they fit up in CAD:




Interference with the firewall plug is minimal, which is nice. Very little work needed there:



As expected, there's tons of interference with the cabin air filter housing. This one will need significant modifications:




Fortunately, it looks like I can keep the stock cable tray! I was not looking forward to redesigning that part:



Of course, not all good news. Braces interfere significantly with the air filter:



Looks like if I raise the rear by 30mm, it'll clear:



Mocked up what that would look like with some spacers and I might be able to pull it off:




The rear edge doesn't really seal with it propped up and the air flow over it looks like it would be greatly reduced



I don't know if spacing up is the right solution. I need to give this more thought. Might need a more substantial redesign of this interface on the cabin air filter housing.

[heinzboehmer]

To do something like this, you’d want to modify the auxiliary fan support to tie the two frame rail attachments into the upper core support, then triangulate that to the strut towers. Then you’d need to essentially build a mini front subframe that could tie back to the frame rails in front, or maybe pick up on the sway bar mounts as that’s what’s doing the frame rail twisting. Tie that mini front subframe into both the aux fan support and the existing subframe. A lot of work.

BMW does something similar to what you describe with their modern cars. Here's a G30 for reference, since that's the simplest implementation I came across during my research:



They skip the "mini subframe" thing you're talking about and just do the frame rails to the radiator support part. Probably because the actual subframe is extremely beefy and spans a good chunk of the front end. Other cars like the G80 have a separate v brace going from the frame rails down to the subframe.

But anyway, the G30 braces go from the top of the frame rails to the top of the radiator support and then another set of braces go to the strut towers.

Forward facing strut tower pickup points on the E46 would be fairly easy to do by bonding in the E85/6 brackets (or similar):



But yeah, sounds like packaging would be pretty hard. I think there might be room to squeeze the diagonal braces in between the aux fan and the kidneys, but can't say for certain. Then you'd need to clearance a good chunk of the front shrouds to be able to snake the strut tower braces through.

[Bry5on]

Man, good question. You can see how well supported the frame rails are with the stamped and tubular braces, then that it is boxed in to the strut towers and the lower subframe and frame rails. This would be pretty effective in torsion but I’d wager less so than the things we’ve already done. Also way harder to package in the e46 engine bay I think.

To do something like this, you’d want to modify the auxiliary fan support to tie the two frame rail attachments into the upper core support, then triangulate that to the strut towers. Then you’d need to essentially build a mini front subframe that could tie back to the frame rails in front, or maybe pick up on the sway bar mounts as that’s what’s doing the frame rail twisting. Tie that mini front subframe into both the aux fan support and the existing subframe. A lot of work.

[George Hill]

As you can see the F8X has a much beefier front crossmember/radiator support that the E46 which is long spans of flimsy thin gauge steel. I wonder how much of a benefit there is in improving that.

Bry5on

[bigjae46]

It seems like it's one of those big generational jumps. E9x is way stiffer than E46 and every car of the E9x era has some version of these triangulation braces. E85/6 is a weird E46/E9x hybrid and it lucked out with the E9x chassis rigidity.

Think we're just slightly too old and missed out on that.

Also, just for fun, this is the bracing in the F80 M3. Again, way stiffer than the previous gen, but man, it essentially needed a full exoskeleton to get there:

As you can see the F8X has a much beefier front crossmember/radiator support that the E46 which is long spans of flimsy thin gauge steel. I wonder how much of a benefit there is in improving that.

[heinzboehmer]

I am curious why it didn't come from the factory. As in, the Z4M did, and wasn't that much later.

It seems like it's one of those big generational jumps. E9x is way stiffer than E46 and every car of the E9x era has some version of these triangulation braces. E85/6 is a weird E46/E9x hybrid and it lucked out with the E9x chassis rigidity.

Think we're just slightly too old and missed out on that.

Also, just for fun, this is the bracing in the F80 M3. Again, way stiffer than the previous gen, but man, it essentially needed a full exoskeleton to get there:

[Slideways]

I am curious why it didn't come from the factory. As in, the Z4M did, and wasn't that much later.

E85s started production in 2002, a good 5 years after the E46 (1997).

[Obioban]

I am curious why it didn't come from the factory. As in, the Z4M did, and wasn't that much later.

[heinzboehmer]

Ok...now I get what you are trying to do. Skim the OE part, make a layer that the thinner OE part can sit on that will provide the mounting point for the E86 bars. I know...I'm dense sometimes or at least that's what my wife tells me...lol

Yep! That's exactly it. I have a bunch of left over adhesive from the windshield mount, so I'll likely bond the skimmed OE part to my custom part, for that last little bit of extra stiffness.

Just need to figure out how to combine that with powder coating. I haven't found a reference where 3M outright states the operating temp range that 07333 is intended to work at, but the data sheet seems to imply that it shouldn't be exposed to temps higher than 80 C. Might need to get everything painted instead of powder coated because of this, we'll see.

Bro…I LOVE IT!!!

And thank you! I'm honestly really, really happy with how this turned out. Looks like it could have come like this from the factory.

[bigjae46]

Finally got myself in the machine shop.

3D printed fixture worked incredibly well. I could have probably made it half as stiff and it would have still been totally fine. Playing musical bolts to get to the bosses was a bit annoying, but no big deal

Machine operator worked okay. I do have experience on a mill, but this is my first time ever on one without supervision, so go easy on me.

Ended up removing 4.5 mm from bosses to new flat surface. This is 0.75 mm more than I had originally thought I would need, but that's totally fine with me. My brackets will be 4.75 mm thick, so the final assembly will sit pretty much exactly where the stock ones do.

I did forget one thing when designing the fixture. The strut bar surface is angled on two separate axes compared to the strut tower surface, so the fixture needs clearance on the sides as well to be square on the vise when using those two reference cuts I added. Got around that with some creative shimming, but this was far from the stiffest setup, as you can probably tell.

My "lightest of skims" turned into a 0.75 mm cut, which I'm not thrilled with. I fell into the trap of trying to get the surface flat with a subpar setup and removed more than I wanted to. I kinda wish I had just flattened the high spots with a file, but oh well. It shouldn't really make a difference in the end, but lesson learned.

With the final dimensions of the stock brackets known, I jumped into CAD and adjusted my brackets. No big design changes, just some planes moving around a bit:

Ok...now I get what you are trying to do. Skim the OE part, make a layer that the thinner OE part can sit on that will provide the mounting point for the E86 bars. I know...I'm dense sometimes or at least that's what my wife tells me...lol

[bigjae46]

Bro…I LOVE IT!!!

[heinzboehmer]

Also, this is worth pointing out.

I started this whole project because I didn't like that the Slon brace requires that you remove the strut tower brackets to work on the engine. At this point, I've removed and resintalled my strut tower brackets dozens of times. The irony is not lost on me.

I have to admit I was mistaken. Removing the brackets frequently is nowhere near as annoying as I thought it would be. Yes, there's a chance you can lose your alignment, but as long as you keep the tires on the ground (or plan ahead and temporarily bolt the stock brackets on before lifting the car), it's not a problem at all.

And yes, I've likely spent about as much money developing this as I would have just buying the off the shelf solution.

Still 100% worth it though. I've learned a ton doing this and I really like the subtlety of this solution. Can't wait to have it 100% complete.

[heinzboehmer]

I know I've test fit these things fifty million times now, but having the stock brackets machined got me excited, so I printed up plastic versions of my brackets and fitted everything to the car.





This picture gives a rough idea of how the engine bay will look when everything is ready. I'm a huge fan of how subtle this mod is:



And this one gives a good sense of how tight the clearances are:



Windshield wipers work no problem:

Have tomorrow and Friday off, so I'll scan the engine bay, the cabin air filter housing and the firewall plug. Then get lost in CAD land for a while, figuring out what needs clearancing where.

Also, got this in the mail today:



Will be waiting for me in the stash until the time comes to do my head gasket.

[heinzboehmer]

Are you using a maker space? I had access to one in Wichita, KS. It was outstanding! Wish I had something here in Houston. All the ones I've found require you to be a college student.

Did this at the machine shop at work.

I'm surprised about the college student thing. Over here, the maker spaces don't care who you are. All they care about are your monthly membership fees

[bigjae46]

Are you using a maker space? I had access to one in Wichita, KS. It was outstanding! Wish I had something here in Houston. All the ones I've found require you to be a college student.