Black & Tan 332iT

[Obioban]

Seems like the vert brace is missing some mounting holes?

[heinzboehmer]

https://www.motorsportparts.nl/bmw/bmw-e46-z4/body/e46-dubbele-tunnelbrug---1-stuk

Been done already, karter16

Oooh, very nice. Thanks for the link.

Any idea on weight? Convertible piece is 0.946 kg according to realoem.

[bmwfnatic]

In case you want to do some more pondering: https://wilhelmraceworks.com/blog/me...ssis-stiffness

I'm currently pondering about the best way to build a similar thing for myself to get data from my car. Would be awesome to be able to quantify these changes instead of trying to feel them out.

About the tunnel brace, I think a plate sandwiched between the stock parts would yield the most gains for the least effort. Boxing the stock parts in would be even better, but that requires welding. Non-M part is likely the best answer though.

https://www.motorsportparts.nl/bmw/bmw-e46-z4/body/e46-dubbele-tunnelbrug---1-stuk

Been done already, karter16

[Bry5on]

I think I used M8x1.25 x 16mm button (and e-torx, because why not make it complicated) head screws, I will have to double check length. Then just M8x1.25 rivet nuts with 2mm ground off the nose so that they’d fully seat into the subframe before hitting the upper wall. Installed wet with POR-15 to prevent rust just in case.

edit: I ordered some of these to test grip range. Will report back: Low-Profile Rivet Nuts, Tin-Zinc-Plated Steel, M8x1.25 Internal Thread, 15.2mm Long

https://www.mcmaster.com/91230A011

Ok this is definitely the right part for this application. Should fit in the available space and installs into a .500” hole

[Bry5on]

What hardware did you use?

I think I used M8x1.25 x 16mm button (and e-torx, because why not make it complicated) head screws, I will have to double check length. Then just M8x1.25 rivet nuts with 2mm ground off the nose so that they’d fully seat into the subframe before hitting the upper wall. Installed wet with POR-15 to prevent rust just in case.

edit: I ordered some of these to test grip range. Will report back: Low-Profile Rivet Nuts, Tin-Zinc-Plated Steel, M8x1.25 Internal Thread, 15.2mm Long

https://www.mcmaster.com/91230A011

[heinzboehmer]

Alright, here’s a link for those in the US where you can purchase this v-subframe brace directly if you so desire: https://cart.sendcutsend.com/styxqbkx1nth

Reminder, this link is not me selling anything, I make no money on this, and I’m not affiliated with sendcutsend other than really liking their service.

What hardware did you use?

[Bry5on]

Alright, here’s a link for those in the US where you can purchase this v-subframe brace directly if you so desire: https://cart.sendcutsend.com/styxqbkx1nth

Reminder, this link is not me selling anything, I make no money on this, and I’m not affiliated with sendcutsend other than really liking their service.

[heinzboehmer]

I was pondering torsional rigidity last night - do you think there would be anything at all to be gained by replacing the 2x transmission/exhaust tunnel brackets with a single torsion plate across those 8x mounting points? Not from the perspective of preventing the tunnel from spreading out /collapsing in but in terms of helping to prevent longitudinal twisting? In theory it would make a non-zero difference, but the two brackets are fairly close together so not sure if there would be much, if anything, to be gained in practice? The non-M3 convertible had a similar sort of thing (although I believe that was only 4x mounting bolts not 8). BMW didn't do that on the M3 vert though so 🤷♂️

In case you want to do some more pondering: https://wilhelmraceworks.com/blog/me...ssis-stiffness

I'm currently pondering about the best way to build a similar thing for myself to get data from my car. Would be awesome to be able to quantify these changes instead of trying to feel them out.

About the tunnel brace, I think a plate sandwiched between the stock parts would yield the most gains for the least effort. Boxing the stock parts in would be even better, but that requires welding. Non-M part is likely the best answer though.

[Obioban]

Ordered a couple

[Obioban]

Thanks!

[Bry5on]

3D file attached as well, by request

[Bry5on]

Here you can see more clearly how I got my bends incorrect. When bent correctly, the holes should be offset right and pretty centered around the subframe drain hole.

[Bry5on]

I really have no concept of what kind of loads the hardware is being subjected to here. Sheer point of a M6 bolt is ~2000 lbs, and we have two of them-- Do you think we actually need M8 hardware?

Semi related: CAD file or sendcutsend link?

Awesome idea! I'm increasingly convinced that torsional rigidity mods are second only to weight savings-- and they come with much less cost/trade off.

I think M6 is likely not going to fail honestly, but the bearing area under the fastener head is pretty small, so the joint could slip. I also don’t have a good sense of the loads, but I can tell you that if I don’t push hard on the x-brace toggle clamps to tension up that joint, I can hear the joint slip in the cabin.

I also totally agree with you on torsional rigidity being of high importance. My stock M3 springs feel surprisingly firm now after reducing the “chassis as a spring” effect. These low weight (lighter weight for Slon brace!) mods are netting massive benefits. I would prioritize these changes over aftermarket suspension all day any day for any car.

I’ve requested to share the cart from sendcutsend, but here’s the DXF for now. I’m going to need to re-do that sendcutsend cart as I forgot the bracket isn’t symmetrical and mine is bent upside down. No functional change, but the two subframe fasteners aren’t centered in my car for aesthetics

edit: all six bends are 90 and in the same direction

[Obioban]

I really have no concept of what kind of loads the hardware is being subjected to here. Sheer point of a M6 bolt is ~2000 lbs, and we have two of them-- Do you think we actually need M8 hardware?

Semi related: CAD file or sendcutsend link?

Awesome idea! I'm increasingly convinced that torsional rigidity mods are second only to weight savings-- and they come with much less cost/trade off.

[Bry5on]

I made it over to the lift today, drilled out those M6 rivet nuts and replaced them with the M8 I'd originally intended. There's not quite enough room for the rivet nut to insert all the way, so I had to nip 2mm off of them so that they'd fully seat before I riveted them in. Tight squeeze!

Also, today I took the Porsche anti-squeal pads off of the rear of the car in addition to removing the ones on the front. They were on top of the textar anti-squeal pads already bonded to the brake pads. Of course the brakes got noisy coming to a stop after I removed the front ones, so I gave all 4 pads the sil-glyde treatment today and so far so good. Pad dragging issues are FINALLY GONE and the pedal feel is a bit nicer. Whew, only a year and a half to solve that one.

Do NOT add the Porsche anti-squeal pads to your 996 textar brakes!!