DIY: Slonik E9X CF Reinforcement Panel

[SYT_Shadow]

I finally got around to installing the CF panel! There a GB going around so it's a good time to get it done and provide some instructions.

From the E9X to the F8X generation there was an increase in torsional rigidity. Both are very rigid, but I’ve been jealous the F8X is a 20% stiffer!
Looking at data, the E9X is 33000Nm/deg and the F8X is 40000Nm/deg

In some cars like the previous gen M5, BMW did not offer a folding rear seat, with the goal of increasing the car’s rigidity.

My track E90 has fold down rear seats like every E9X, although the rear seats are removed in its current config.

Audi uses a CF panel to increase torsional rigidity by a whopping 33% in its A8... what about doing that on the E9X?
Enter Slonik’s CF reinforcement panel!








Specs:
-Vacuum infusion with post-curing
-Base options – oem look plain wave, small or large size twill wave (the latter was my choice). Any other options on request at time of order
-Can be installed behind oem seats if desired, no need to rip up your interior or irreversibly turn your car into a track-only machine
-Installs with structural epoxy, which can be removed with a heat gun
-Has a sweet ///M in the panel so no one is confused about who builds your grocery getter
-Weight below 4lb (1.7kg)
-Thick enough - about 2.5millimeters of pure carbon layers.


LIST of materials needed for install:
180 grit sand paper. I use the foam block style.
Alcohol and microfiber cloths (having a source of water handy helps)
BMW SF-7888 (K-3) structural glue and applicator gun. This is the same glue I used for the CF roof install (https://www.m3post.com/forums/showthread.php?t=1792840) a few weeks ago, and the same glue BMW recommends for installing CF onto steel panels in their cars.
Locking pliers, 1/4", x4
Rubber gloves
Tyvek full body suit (Home Depot) and N95 mask for sanding CF


Steps:
First fit the wall with no glue to see more or less where it goes
Use masking tape to seal off the area around the wall where glue does not go. This is not strictly necessary but will make cleanup a lot easier. Protip: use more masking tape than I did, especially in the bottom... that glue drips everywhere! :S
Use masking tape to seal the wall on both sides. Anywhere you don’t want glue should be taped up
Sand CF mating surface while wearing special suit and mask
Sand car’s mating surface. Clean CF and car's mating surfaces with alcohol
Heat up the BMW K3 glue. I used really hot water for 30 min.
Stage 1 -put glue on the sides, bottom, top of the car’s mating surface
-put glue on the wall, only bottom and half of the side
-put locking pliers on top both sides and something on the bottom to hold the wall tightly
Stage 2: -from the trunk, apply glue to all the perimeter, push it in with your fingers (with a glove on)
Clean Up: remove the masking tape and plastic sheeting from both sides. Be careful not to get epoxy on random surfaces. Change your gloves often.


Like everything Slon Workshop/Slonik makes, this is a real piece of art








Here's a pic of the BMW epoxy that is used. K-3





We start by taping up both sides of the wall. We don't want any rogue epoxy getting on the CF








We test fit it just to make sure we understand where it goes. Also, while it's in place we mask up both sides of the car so the epoxy doesn't overflow and mess everything up later. This takes a while but I think it's the easiest solution. Again, use more masking tape than I did in the bottom area!







Remove the reinforcement wall from the car and look at the mating surfaces




Get a 180 grit sandpaper block and rough up the part of the car where the glue goes. The objective is to roughen it up, not sand all the paint off, so take it easy. When finished, get a microfiber cloth and alcohol to clean up the surfaces and ensure they are clean


Now you have to do the same thing to the CF reinforcement wall. Sanding CF is nasty business, so we put on the Tyvek full body suit we got at home depot, goggles and an N95 respirator, then start sanding the panel's mating surfaces. After sanding we clean the surfaces with alcohol.
Remove the Tyvek suit and throw it away, then change your gloves


Now get the epoxy that's been heating up for 30 min, put it into the applicator gun and start applying it. We need to apply it both to the car and also to the CF panel. The CF panel's side and bottom get glue and then the car gets glue as well.
Note we are not double-gluing. There are parts in the wall perpendicular to each other, same as the car. We put a glue bead on the car's surfaces and then another glue bead on the wall's bottom and side which are angled differently.
Once you apply epoxy you're on the clock. Figure you have 20 minutes of set time to work, after that it gets dicey.
Once you put the wall against the body and the glue starts doing its thing, we apply some locking pliers/clips to the top surface to hold the wall in place, then I used a piece of wood going from the front seats to the wall to apply pressure










After this step you need to go to the back side of the wall: in through the trunk and apply a second stage of glue to make sure all the voids are filled in. I put extra glue all over and then used a glove to press it into a more or less clean bead with my finger. You do this on the bottom, both sides and the top through the trunk

After that it's cleanup time! You want to remove the masking tape from the car and from the reinforcement wall. Be careful because the tape is messy, this will require you to change gloves many times. Eventually you finish!
















Finally, I left it to dry for a few days without moving the car



More info:

Idea of this rear wall was born after watching on e46 torsional rigidity figures:

E46 Sedan (w/o folding seats) 18000
E46 Sedan (w folding seats) 13000
E46 Touring (w folding seats) 14000
E46 Coupe (w folding seats) 12500
E46 Cabrio 10500
What do we need to see here? Comparing two sedans' torsional rigidity – the difference between two chassis is limited to the steel wall behind the rear seats! 38% increase of torsional rigidity with only one chassis element difference!
Another interesting fact is that e46 coupes and even e46 m3s don’t have chassis options without folding seats (with the factory wall). Same for the next generation e9x chassis – bmw didn’t offer “w/o folding seats” option at all, so all versions have a hole instead of a wall.
Second comparison of the two chassis, which has a difference in the roofs – one has steel installed with spot welding, second one – glued with structural glue carbon fiber roof panel.
E46 M3 18500
E46 M3 CSL 18750
These are the factory figures, and BMW shows us that a carbon fiber panel installed with the structural glue give us even more stiffness than spot welded steel.
So the idea was to make the a unique product, inspired on the factory engineered chassis solution.

It’s important to note the main idea of this product was to get noticeable improvements in torsional rigidity of the body and at the same time, make a street compatible solution without transforming it into a track only car.
This is why the stiffness wall was designed to be compatible with the rear seats.

In the end, our beloved cars had a great chassis in their time, but time moves on. This is like an anti-ageing upgrade to stay competitive vs more current generations' cars.

[SYT_Shadow]

reserved

[DRLane]

Awesome write up! How are you always 1 step ahead of Mathieu's GBs? Anyhow, beautiful piece!

Btw, I'm very jealous of how clean your trunk and back seat area are! I have work to do...

[SYT_Shadow]

Originally Posted by DRLane

Awesome write up! How are you always 1 step ahead of Mathieu's GBs? Anyhow, beautiful piece!

Btw, I'm very jealous of how clean your trunk and back seat area are! I have work to do...

It's because after 6 months of sitting on a piece, Matt does a GB and I feel so guilty that I stop doing other things to the car and just get it done!!

Unless I've had a part for a good 6 months in the basement collecting dust I'm not ready to install it

[Epoustouflant]

Originally Posted by DRLane

Awesome write up! How are you always 1 step ahead of Mathieu's GBs? Anyhow, beautiful piece!

Btw, I'm very jealous of how clean your trunk and back seat area are! I have work to do...

SYT's one step ahead, every time - the definition of an innovator.

Amazing write up. You mind if I share some pics in owners groups?

[SYT_Shadow]

Originally Posted by Epoustouflant

SYT's one step ahead, every time - the definition of an innovator.

Amazing write up. You mind if I share some pics in owners groups?

Please go ahead and share the pics as you see fit. It's a beautiful piece!

[Redd]

Awesome work SYT! I love how Slonik goes to the trouble of putting the ///M logo in a different weave just so that it stands out more. Definitely a work of art.

[SYT_Shadow]

Originally Posted by Redd

Awesome work SYT! I love how Slonik goes to the trouble of putting the ///M logo in a different weave just so that it stands out more. Definitely a work of art.

You have a sharp eye!

[rhyary]

Great write up!
Thank you for sharing

[Rochen_00]

Amazing! It looks like a work of art to me, and with the M logo it looks spectacular.

Very good job SYT, looks awesome

[M43S7RO]

Great write up! Im a sucker for improving chassis rigidity & reached out to slon when I saw this on his ig. Got it in a few months ago, quality really is top notch & slon was accessible with questions that I had about the install. One thing I did different is I used ratcheting cargo bars from harbor freight to push & hold the lower corners in place while the epoxy set.

Bottom picture is my take on a rear seat delete for a street car. I bought a set of used e92 lower seats and bolsters for pretty cheap and wrapped in suede material. Kept my oem parts in case I get that "what was I thinking" feeling one day, I can easily revert to stock interior.

I have solid subframe bushings, upgraded suspension bushings almost everywhere else and stiff springs and so from my experience it is hard to perceive the difference this makes if you are looking to feel it. For me it is more about the fact that a more rigid chassis allows the suspension to do the work.

[SYT_Shadow]

Originally Posted by M43S7RO

Great write up! Im a sucker for improving chassis rigidity & reached out to slon when I saw this on his ig. Got it in a few months ago, quality really is top notch & slon was accessible with questions that I had about the install. One thing I did different is I used ratcheting cargo bars from harbor freight to push the lower corners while the epoxy set. Bottom picture is my take on a rear seat delete for a street car. I bought a set of used e92 lower seats and bolsters for pretty cheap and wrapped in suede material.

I have solid subframe bushings, upgraded suspension bushings almost everywhere else and stiff springs and so from my experience it is hard to perceive the difference this makes if you are looking to feel it. For me it is more about the fact that a more rigid chassis allows the suspension to do the work.

Wow! That looks spectacular. And good idea with those bars holding the bottom edges together!

[Richbot]

I'm sure Motorsport looked at it and went :"eh, anybody competing even semi-seriously in one of these will be caging it anyway, this is a 400+hp car, you'd be crazy not to"

And then *gestures at track forum*

Also, E90M's *were* available without the folding rear seats. It was an option, included in the cold weather package, or as a separate line-item option. 2008 order guide here. I've only seen one in the wild without them.

https://www.google.com/url?sa=t&rct=...yiZuDbRwlv30Uj

So, you bought the *wrong* E90M for track work, and should just give up and start over once you find one optioned correctly. I'll give you $1500 for yours so it's not a total loss.

[wyatth]

I have an E90 without folding rear seats (of course BMW makes them standard in the coupe and optional in the practicality-driven sedan). Don't really mind since I never haul stuff in the E90 anyway. That said, I don't think the folding rear bench or fixed rear bench makes much difference in the E90. In previous gens, the chassis seemed modified and you could not easily swap folding benches between cars. In the E90, it's quite simple which makes me think the chassis is identical. And since the seat back itself isn't structural, theres's probably minimal torsional rigidity gained with fixed back in this car. That doesn't mean filling the void with something like this carbon panel won't help, but it's not the same as filling the void in an E46 with folding rear seats.

I totally need this behind my son's carseat.

[derbo]

Originally Posted by Richbot

I'm sure Motorsport looked at it and went :"eh, anybody competing even semi-seriously in one of these will be caging it anyway, this is a 400+hp car, you'd be crazy not to"

And then *gestures at track forum*

Also, E90M's *were* available without the folding rear seats. It was an option, included in the cold weather package, or as a separate line-item option. 2008 order guide here. I've only seen one in the wild without them.

https://www.google.com/url?sa=t&rct=...yiZuDbRwlv30Uj

So, you bought the *wrong* E90M for track work, and should just give up and start over once you find one optioned correctly. I'll give you $1500 for yours so it's not a total loss.

From what I recall, the non-folding rear seat E90s were fundamentally the same chassis wise. This was not the case in E46 were they were structurally different.

[SYT_Shadow]

Originally Posted by Richbot

I'm sure Motorsport looked at it and went :"eh, anybody competing even semi-seriously in one of these will be caging it anyway, this is a 400+hp car, you'd be crazy not to"

And then *gestures at track forum*

Also, E90M's *were* available without the folding rear seats. It was an option, included in the cold weather package, or as a separate line-item option. 2008 order guide here. I've only seen one in the wild without them.

https://www.google.com/url?sa=t&rct=...yiZuDbRwlv30Uj

So, you bought the *wrong* E90M for track work, and should just give up and start over once you find one optioned correctly. I'll give you $1500 for yours so it's not a total loss.

M3Post: "hold my beer"

You're right, there was an option for non folding seats!

[Richbot]

Originally Posted by derbo

From what I recall, the non-folding rear seat E90s were fundamentally the same chassis wise. This was not the case in E46 were they were structurally different.

But if you have folding seats you can't claim 1337 stripper track special CSL status, those latches and cables and stuff are almost as heavy as an amp bracket with no holes in it

[derbo]

Originally Posted by Richbot

But if you have folding seats you can't claim 1337 stripper track special CSL status, those latches and cables and stuff are almost as heavy as an amp bracket with no holes in it

Civic CX spec

[Richbot]

careful getting too close to EG-OGness or ur car will get stole

[dogbone]

Fantastic....where do my skis go now???!!!! Oh wait I don't ski!

Great stuff!!

[Epoustouflant]

Originally Posted by dogbone

Fantastic....where do my skis go now???!!!! Oh wait I don't ski!

Great stuff!!

Rooftop 😂 style points

[Biginboca]

This is really cool! I picked up a Cusco rear strut brace because I deleted the rear seats also, I wonder how the rigidity compares between them. The Cusco is just a cross rod that connects the 2 stock black side braces (the ones from the fender tops to the side panels).

What’s great about this panel you have installed is it also kills 2 birds with one stone, you get a rear seat delete panel as well... and obviously looks killer too!