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

[terra]

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.

Wheelbase itself is about the same

[Icecream]

Wheelbase itself is about the same

I think firewall to bulkhead is more critical dimension.

[terra]

I think firewall to bulkhead is more critical dimension.

I’d be surprised if that’s truly significantly different. The overall length difference is mostly the bumpers sticking out a little further.

[old///MFanatic]

Wheelbase is used for the testing. If I remember correctly, Structural Rigidity numbers are only tested within its wheelbase, where the loads are applied by the suspension. The ends or “overhang” at the ends doesn’t contribute to a car’s core strength that’s measured in the test.
Basically it’s done at the four wheel wells. Ours had the back two fixed and the front gets one wheel dropped and deflection/twist measured.
Maybe it’s changed recently but that’s how’s testing was measured.

[PetrolM3]

I never realized how much difference the rear bulkhead makes until I got my non-folding sedan after years of M3 ownership. Driving the two cars back to back, I felt that the non-folding sedan was much more rigid than the M3 despite the numbers released by BMW.

However, as one of the methods to combat the RACP issue on the M3, I decided to get a Mason GTR brace which ties the rear subframe to the shock towers. This brace is a quality replica of the original part found in the E46 M3 GTR. My first drive in the car post brace install blew my mind as to how dramatically the brace increased the rigidity of the M3. It is still one of my favorite mods simply due to increase in rigidity and how the car feels.

I'm not sure how much more or less effective the Slonik CF panel would be for rigidity increase but it sure looks like a nice rear seat delete option. However, for those who want to use their folding seats, or for the sake of reversibility, the GTR brace makes more sense whether you leave it installed or remove it when needed (it takes 15 minutes). At 6 pounds, I doubt it's much heavier than the CF panel (at least the aluminum version; they also make a steel variant) and it costs significantly less. It also addresses part of the subframe issue in a very clean way versus the invasive alternatives such as the Vince bar and other similar products. PS. I don't work for Mason - I simply love this product and highly recommend it!

Interestingly, the GTR road cars (I think only 10 were made for homologation reasons) seem to be the only E46 coupes which did have the rear bulkhead from factory, but they also had the brace - likely to keep the subframe from ripping out considering they had quite a bit more torque than a standard M3. Pics of the brace and the bulkhead can be seen at the following link: https://www.supercars.net/blog/2002-...trasenversion/

The GTR race cars did not have the bulkhead but did have the brace in place along with a full cage and torsional rigidity of 46,000!

I'm honestly surprised that BMW didn't install this brace in the CSL, or at least offer it as an option...

Mason GTR brace: https://www.ebay.com/itm/MASON-ENG-E...-/273182400526

[Icecream]

I never realized how much difference the rear bulkhead makes until I got my non-folding sedan after years of M3 ownership. Driving the two cars back to back, I felt that the non-folding sedan was much more rigid than the M3 despite the numbers released by BMW.

I'm honestly surprised that BMW didn't install this brace in the CSL, or at least offer it as an option...

Mason GTR brace: https://www.ebay.com/itm/MASON-ENG-E...-/273182400526

I don't know about the first part, you probably just drove a tighter sedan. Agree though, find it odd the CSL was not stiffened more if so simple.

[0-60motorsports]

Very Nice and i am sure the quality is beautiful but for that price Hard pass. As our cars get older (and me too) I am actually starting to slowly return some parts to stock lol.

[ZHPizza]

I don't know about the first part, you probably just drove a tighter sedan. Agree though, find it odd the CSL was not stiffened more if so simple.

Just to throw in another subjective data point:

I had a ZHP sedan with the solid rear seatback and it was a very noticeable difference in feel. The turn-in felt great with that stiff chassis, even with worn suspension.

I recently added an SME X-Brace to my ZHP coupe and it made a big improvement. Feels much more like the bulkheaded sedan now.

Had I been thinking when I installed it, I would have taken the time to tie some strings in an X across the rear seat opening, lift a corner of the car, measure the droop, then repeat with the X-Brace installed to see how much less droop you get. Could give a nice idea of how much stiffness you gain across that opening.

[Slonik]

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

Notable the Audi A8 is like 2.5 times larger area than the product being discussed here.

yeah, right, cause you have the steel shelf from factory already. we can also remove it and make larger section of carbon fiber, like audi makes. but this will not make such noticeable difference in torsional rigidity, compared to our present solution when we have carbon/steel section. and anyway, how many people will goes on that solution? okay - me. and somebody else? i think another one or two of our regular customers, which e46's stays in our workshop, who can say, "wow, i want it! so, lets fit it in my e46 also!".
so, let's be little bit more realistic - idea was to get max result and same time stays bolt-on solution, which already happening on the edge, due to the user's about zero experience with the structural bonding .

The Audi sedan one is 6-19 layers of carbon fber that is affixed to some 7 walls and 2 separate planes.

to understand "why", you need to be more attentive - audi's wall have the hole in the center, so they had a LOT harder task, to get same stiffness as on the wall without the hole.

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.

how do you think, panel with same stiffness will give similar gains in percent on 18000nm/deg body and for example on 40000nm/body?

"The flagship’s torsional rigidity – the critical parameter for precise handling, pleasing acoustics and top workmanship – surpasses its predecessor model’s rigidity value by up to 24 percent"
predecessor model - Audi A8 D4 45,000 nm

so, A8L generation with carbon wall has fantastic 55800nm/deg!
and even on those overall figures, their wall gives another 30% of torsional rigidity.


but anyway, we are continue to work on real testing figures.

[Slonik]

6-19 layers thick of CF

to understand, why 19 layers:

[usdmej]

find it odd the CSL was not stiffened more if so simple.

hate to keep saying the same thing over and over again, but they put effort towards lightening the rear seat considerably while still maintaining fold down functionality, indicating that pass through functionality was not something they were interested in deleting

[Icecream]

hate to keep saying the same thing over and over again, but they put effort towards lightening the rear seat considerably while still maintaining fold down functionality, indicating that pass through functionality was not something they were interested in deleting

While that may be true the only way it makes sense for them to do that is if putting a bulkhead there would yield negligible performance increase, then I could understand why they would go through the trouble. Otherwise it was just a bad call on BMW's part, which could be but seems unlikely. Nobody is carrying broomsticks in a CSL and I doubt any CSL has ever had the seats folded down. But I guarantee everyone of them has been to the track.

Dealer: "Sir, this CSL has a carbon roof, lighter seats, carbon interior, no AC, no radio and is the ultimate lightweight track weapon to beat up GT3's with"
Buyer: "yeah but does the rear seat fold down though?"

I don't know about you but I don't think that is a possible conversation lol.

[ZHPizza]

While that may be true the only way it makes sense for them to do that is if putting a bulkhead there would yield negligible performance increase, then I could understand why they would go through the trouble. Otherwise it was just a bad call on BMW's part, which could be but seems unlikely.

I mean even if there was no possibility of a stiffness increase they could have shaved several pounds off of the back seat if they got rid of the hinges/latches/etc that goes into making the fold down option work. They were already making a completely new design so someone high up must have said the pass thru was a requirement. I agree that it seems silly af tho.

[usdmej]

Dealer: "Sir, this CSL has a carbon roof, lighter seats, carbon interior, no AC, no radio and is the ultimate lightweight track weapon to beat up GT3's with"
Buyer: "yeah but does the rear seat fold down though?"

I don't know about you but I don't think that is a possible conversation lol.

a more realistic conversation BMW was trying to avoid was

Dealer: "Sir, this CSL is every bit on par and maybe even better than a GT3 on track"
Buyer: "then why don't i just buy a GT3?"

[EnzoAtMonza]

Did this close? Did we make it to 20?

Jeff