DIY - Chassis reinforcement ideas

One thing I notice when driving the car hard on tight twisted roads is that the chassis flexes. As I’m about to get my car repainted I was wondering what people have found to be the most useful for chassis strengthening. I know Coupeking is doing that almost as standard procedure. A lot of the work seems to be around adding welds to things like the rear wheel well to the bulkhead behind the rear seats. I’ve also seen a triangle shape being added in the engine bay between the frame rail and the firewall.

Does anyone have any experience to share in that area?
 
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eriknetherlands

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In my view the additional tube does not really help. it is putting a beam *inside* another beam. As an engineer that is the most hopeless place to add mass; in the center of the element! It is however easy; weld it in & forget. It also helps tremendously when you're hit from the side by a low nosed car like a Ferarri.
I considered it also; I even bought a roll cage quality tube for it but choose not to go that route. It's easily 15 kg of mass added to the car; too much for me.
Also the corrosion aspects of such a modification are tricky. The inside of such a tube and between the tube and inner sill it can hardly be protected effectively by DIY techniques; only an acid dip and paint dip will work for such enclosed volumes.

The sill itself isn't really weak I think. what makes the body weak is that the various stiff parts (Vertical A-pillar, frame rails, tunnel, sills, firewall, front struts) aren't rigidly connected to each other. Our e9 chassis are missing triangle shaped links between these various components, we have just nearly flat sheets of 0,8 mm metal. Think of forces flowing through a body following the lines that are visible in tubular designs as the Maserati birdcage and 300SL.
Besides what is already mentioned, i see a few places on an E9 body that could be improved in my view:
- top of tunnel (around gear shift) to corners of the upper firewall/ upper a-pillar (but there is a lot of stuff in the way).
- frame rails to sills, directly connecting lower A-pillar to the frame rail near the firewall, and another triangle hiding under seat structures. (serious 3D metal crafting)
- the rear diff mount, as done for instance with the Coupe King solution.
 
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Gazz

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Agree. This is an an engineering exercise. The challenge is to find the structural antidotes to the compromises of the original design. But..... perhaps the original design compromises are not compromises in the sense of efficiency of design and taking the probable brief into consideration. I.e. we have a budget here Ja?
So, what is is the optimal structure without regard to cost, weight. aesthetics, etc?
Good luck with this exercise because what we may end up with is....... an E9. Or not.

Is an E9 an E9? Can it be a better E9?

Perhaps. Perhaps not?
 

dang

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Seems like the issues with the E9 chassis twisting is more like that of a convertible, or lack of a complete "box" for rigidity, or at least a weak upper half. Obviously a box roll cage solves this, but how are convertible chassis' different than coupe/sedan chassis'? Seems like the most benefit would be some kind of diagonals added in the lower corners of the A-pillars and C-pillars both laterally, forward and aft. Basically creating a stiff box with no top. I'm imagining a stick-frame E9 chassis and how it would flex under load.
 

tmh

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In my view the additional tube does not really help. it is putting a beam *inside* another beam. As an engineer that is the most hopeless place to add mass; in the center of the element! It is however easy; weld it in & forget. I considered it also; I even bought a roll cage quality tube for it.
Also the corrosion aspects of such a modification are tricky. The inside of such a tube can hardly be protected effectively by DIY techniques; only an acid dip and paint dip will work for such enclosed volumes.

The sill itself isn't really weak I think. what makes the body weak is that the various stiff parts (Vertical A-pillar, frame rails, tunnel, sills, firewall, front struts) aren't rigidly connected to each other. Our e9 chassis are missing triangle shaped links between these various components, we have just nearly flat sheets of 0,8 mm metal. Think of forces flowing through a body following the lines that are visible in tubular designs as the Maserati birdcage and 300SL.
Besides what is already mentioned, i see a few places on an E9 body that could be improved in my view:
- top of tunnel (around gear shift) to corners of the upper firewall/ upper a-pillar (but there is a lot of stuff in the way).
- frame rails to sills, directly connecting lower A-pillar to the frame rail near the firewall, and another triangle hiding under seat structures. (serious 3D metal crafting)
- the rear diff mount, as done for instance with the Coupe King solution.
The end results of your modifications will be amazing. It will be like driving a different car. How many hours would you estimate you have invested into the modified structural elements? The end result will be worth every minute, so very impressive!
 

Bmachine

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Awesome bits of information everyone! Super helpful.

In terms of the front strut bar between the two front shock towers, would it help to also secure it to the firewall? For example by welding a couple of tabs on the upper firewall near where the strut bar passes so it can be bolted there as well? Or would that create too much stress on an unreinforced section of sheet metal?
 
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eriknetherlands

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Would be very grateful for any info on the strut bar source,
and for the trunk one too...

Regards, Alberto
Daddywad here on the forum makes beautiful front struts; real accurate csl copies.
Walloth and Nesch have more simple and lighter priced options.

Not aware of rear strut reinforcement source, but they are available somewhere.
 

JamesE30

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Daddywad here on the forum makes beautiful front struts; real accurate csl copies.
Walloth and Nesch have more simple and lighter priced options.

Not aware of rear strut reinforcement source, but they are available somewhere.

Daddywad also makes a rear strut brace. A replica of an Alpina one apparently but I’ve never seen pics of a real Alpina one.

EA971D8B-4FA1-4F84-8CC2-AA6C412C79B2.jpeg
 

Gazz

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Here's a pic of my diff to chassis brace. The four bolts are the diff mount bolts. I had to modify the flooring sections by raising them 10mm to clear the bolt heads and the fuel tank lines and wiring. Yes that's also a strut tower cross brace. If you really want to stiffen these cars you have to consider everything.
 

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m5bb

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Here's a pic of my diff to chassis brace. The four bolts are the diff mount bolts. I had to modify the flooring sections by raising them 10mm to clear the bolt heads and the fuel tank lines and wiring. Yes that's also a strut tower cross brace. If you really want to stiffen these cars you have to consider everything.
Now available as a track car?
Wow major work. Good job!
 

JFENG

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what is is the optimal structure without regard to cost, weight. aesthetics, etc?
If you ignore aesthetics I think a multipoint GT3 style racing cage is the quickest/easiest. It ties together key suspension and power train mount points, making the car a partial tube frame. If you’ve driven a tube frame car (even an open top), they have good bending stiffness for their weight.
 

Patton

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Thanks, autokunst.

Ain't real computer-savvy. But I can do some cool things to an E9.
Just gotta get my wife to show me how to post pictures...seriously, not computer savvy.

RP
 

teahead

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These E9s are flexible as hell. I lifted the left corner to mess w/my ps/alt bracketry.

I could NOT open the driver's door.
 

Gazz

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E9s were safety pioneers in utilizing the crumple effect in an impact so maybe I'm doing myself a disservice in rigidifying my car.
 

Bmachine

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Does anyone know how much chassis stiffness the two "bridges" under the seats add? The reason I ask is that I saw @JetDexter and @Patton seemed to have removed those bridges completely in order to mount more modern seat. I'm sure it affects the chassis behavior to a certain degree but I wonder how critical it would be.
 

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autokunst

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Does anyone know how much chassis stiffness the two "bridges" under the seats add? The reason I ask is that I saw @JetDexter and @Patton seemed to have removed those bridges completely in order to mount more modern seat. I'm sure it affects the chassis behavior to a certain degree but I wonder how critical it would be.
I have no scientific data, nor actual tests. But I have removed one side "bridge" out of my bare chassis, and would suggest it is very relevant and a significant part of tying the sills (which are one of the more significant pieces of the puzzle) to the tunnel. Without this connection (and the inherent stiffness that the bridge adds to the tunnel) the whole floor and tunnel can flex quite a bit. Just my observations.
 
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