GB for SLON Workshop CF Rear bulkhead, which can (optionally) be a back seat delete

[terra]

I think you mean the A8 L which is a big four door sedan and not the highly advanced sport coupe.

Notable this is like 2.5 times larger area than the product being discussed here. The Audi sedan one is 6-19 layers of carbon fber that is affixed to some 7 walls and 2 separate planes. As addressed earlier if ///M strengthened the M3 shell to achieve 18,750 nm/deg of Strutural Rigidity with the open trunk it doesn't seem well reasoned to assume adding a small panel insert will achieve the 1/3rd Audi gets here in gains with their twin panel two plane addition.

Seems the theory here is if BMW gets 5,000 nm/deg SR gain with the soild rear bulkhead on the E46 sedans that doing similair will result in the very similar gains. I'm not seing it being that equal. The E46 sedan has a solid bulkhead in the rear. With fold down seats (like coupe) it has side brackets. So it's not completely side to side tied in, but rather an insert. You can view and compare in my link to the ETK E46 Body rear bulkhead on #1 Solid no opening vs #2 with opening for fold down seats.

https://www.realoem.com/bmw/enUS/showparts?id=ET37-USA-03-2004-E46-BMW-325i&diagId=41_1105

It should achieve some structural gains but I can not see if being in the percentage promoted.

Then again these are just my thoughts and reasoning. By saying this I am absolutely open to seeing how I am missing something.

I'm not 100% sure I see what you're saying? Seems to me this panel would be filling in exactly the area that's missing on the fold down bulkhead vs the solid one. I don't know what the gains would be on an M3, but I imagine if you did the mod on a fold-down E46 sedan, the end result would be very similar to a non-fold E46 sedan.

[Obioban]

I did mean A8!

[usdmej]

It should achieve some structural gains but I can not see if being in the percentage promoted.

your observations make sense if you assume that the E46 doesn't have a rear deck that doesn't tie into the car already. with the Slonik bulkhead you're tying it all together, creating a bracing setup similar to the Audi piece.
on top of that, audi's claiming 30% increase in stiffness is on top of using present day (superior) materials and engineering. i think Slonik's claims are reasonable, although if they are able to come up with a number it'd be nice to see any kind of explanation as to how they got it.

[old///MFanatic]

E46 sedan rear body shell solid rear bulkhead.

[old///MFanatic]

your observations make sense if you assume that the E46 doesn't have a rear deck that doesn't tie into the car already. with the Slonik bulkhead you're tying it all together, creating a bracing setup similar to the Audi piece.
on top of that, audi's claiming 30% increase in stiffness is on top of using present day (superior) materials and engineering. i think Slonik's claims are reasonable, although if they are able to come up with a number it'd be nice to see any kind of explanation as to how they got it.

Oh thanks for your reply sir. Yep, would love to see numbers.
In regards to the Audi piece, it is 6-19 layers thick of CF. It is a major structural piece at that point. How many layers of CF is this piece?
It’s really not a good equivalent between the two imho.
As an example the CSL roof adds approximately 250 nm/° over the steel roof. Not 2,500 or even 500. The 250 nm/° is because of the CF material AND the advanced industrial structural adhesive used compared to welds (///M engineers wrote paper on it).
Sure they’re different areas, that’s not lost on me. Nor that they’re entirely different cars(which honestly should have ended discussion there). 😉
Point being it’s not just the material, it’s the thickness and strength of it combined with the dimensions it covers and multiple structural walls it adheres to as well as 50mm wide attachment strips it uses to make contact with the industrial structural adhesive.

Make a one piece 6-19 layer thick CF material panel that’s both the entire rear bulkhead AND rear top deck panel (that shores up the trunk walls). Make it so that it adheres in wide strips all along it’s perimeter with aerospace structural adhesive. Then I’d believe you’d be likely to gain similar. Just my humble opinion.

[timmo]

Number of layers, but what also matters is density (number of filaments per tow).

It'd drive up the cost a bit, but if you want to make it really, really stiff then you can add core to make a sandwich panel. And since it was stated this panel was infused, it wouldn't be too much more work to use a closed-cell foam like Rohacell since that can be added directly to the layup and infuse the entire sandwich panel in one go.

[old///MFanatic]

Well I’m not trying to redesign their product. Nor crap on thread. It’s a beautiful piece and as a rear trunk cover/seat delete with some benefits if fixed as an brace insert. Bought as such compared to other stuff out it’s a gem.

[Obioban]

Oh thanks for your reply sir. Yep, would love to see numbers.
In regards to the Audi piece, it is 6-19 layers thick of CF. It is a major structural piece at that point. How many layers of CF is this piece?
It’s really not a good equivalent between the two imho.
As an example the CSL roof adds approximately 250 nm/° over the steel roof. Not 2,500 or even 500. The 250 nm/° is because of the CF material AND the advanced industrial structural adhesive used compared to welds (///M engineers wrote paper on it).
Sure they’re different areas, that’s not lost on me. Nor that they’re entirely different cars(which honestly should have ended discussion there). 😉
Point being it’s not just the material, it’s the thickness and strength of it combined with the dimensions it covers and multiple structural walls it adheres to as well as 50mm wide attachment strips it uses to make contact with the industrial structural adhesive.

Make a one piece 6-19 layer thick CF material panel that’s both the entire rear bulkhead AND rear top deck panel (that shores up the trunk walls). Make it so that it adheres in wide strips all along it’s perimeter with aerospace structural adhesive. Then I’d believe you’d be likely to gain similar. Just my humble opinion.

The csl roof replaces an existing panel— its entire benefit is from the change of material/bonding process.

This replaces a void. A void that we know when filled is worth 5000nm/deg on the e46 sedan... with a stiffer material and better bonding process than the sedans equivalent.

[Icecream]

The csl roof replaces an existing panel— its entire benefit is from the change of material/bonding process.

This replaces a void. A void that we know when filled is worth 5000nm/deg on the e46 sedan... with a stiffer material and better bonding process than the sedans equivalent.

The one thing that sticks out to me though is, if BMW was so serious about the M3 and they could have made this change and made such significant gains - why didn't they? It seems a no brainer for such a serious car (with ITB's, bespoke engines, suspension, fenders etc) and especially seems it would have been a no brainer for the CSL. But they did not do it, not even on the CSL with all its changes and carbon- which is interesting to say the least. I want this piece to make a significant change since this chassis is getting old and noodly compared to todays cars but some actual data would seal the deal, can't wait to see what you guys think of it once it's installed.

As for the sedan argument, I have not looked closely at wheel base etc but to my tiny brain it seems a mod like this would make a bigger difference on a car with 4 doors to support and stop wiggling instead of two and the spacing from the fire wall to rear bulkhead is longer so again, seems like more room for improvement rather than on the coupe.

[SocalM3e46]

Kind of wish there was a cheaper steel option. Or would an oem sedan bulkhead work?

[Epsilon]

Kind of wish there was a cheaper steel option. Or would an oem sedan bulkhead work?

Was thinking the same. In my head, I'm thinking if a metal fabricator can make something like this for half the cost? Not as premium as the carbon, but it's hidden.

[Obioban]

The one thing that sticks out to me though is, if BMW was so serious about the M3 and they could have made this change and made such significant gains - why didn't they? It seems a no brainer for such a serious car (with ITB's, bespoke engines, suspension, fenders etc) and especially seems it would have been a no brainer for the CSL. But they did not do it, not even on the CSL with all its changes and carbon- which is interesting to say the least. I want this piece to make a significant change since this chassis is getting old and noodly compared to todays cars but some actual data would seal the deal, can't wait to see what you guys think of it once it's installed.

As for the sedan argument, I have not looked closely at wheel base etc but to my tiny brain it seems a mod like this would make a bigger difference on a car with 4 doors to support and stop wiggling instead of two and the spacing from the fire wall to rear bulkhead is longer so again, seems like more room for improvement rather than on the coupe.

The coupe is longer than the sedan and the fold through non M sedan is stiffer than the (always fold through) non M coupe.

I look forward to chassis twister results.

[empty]

Was thinking the same. In my head, I'm thinking if a metal fabricator can make something like this for half the cost? Not as premium as the carbon, but it's hidden.

A metal three dimensional shear plane that welded or bonded in place should produce nearly the same results, just might weight more.


Sent from my iPhone using Tapatalk

[Icecream]

The coupe is longer than the sedan and the fold through non M sedan is stiffer than the (always fold through) non M coupe.

I look forward to chassis twister results.

Of course it is lol. I wish the chassis twister was going to be an independent test but I am looking forward to it as well.

[heinzboehmer]

Any update on the GB?