Exo Car ‘Ghettocet’ Build Guide Part 8: Roll Cage Mount Plates

It is finally here: the fabrication portion of the exo car build. Getting to this point has been quite the process: digging up all of my old equipment and piecing together a functional fabrication space. But with all of the prep work behind me, it is time to build the roll cage. The first step is to build and install the floor plates.

Roll Cage Preparation Revisited

In the last installment, I reviewed a general guideline of what I needed to build a roll cage for the ghettocet. That list ended up growing. I converted the JD2 Model 3 mechanical tube bender to hydraulics using an adapter from SWAG offroad. This also allowed me to mount the bender on an old engine stand, which made the whole unit portable. Finally, my workspace is somewhat exposed to the elements, and I built a wall on the long side to prevent any more rain from getting through. This wall allowed space for a bench to hold items like a tube notcher, grinder, metal saw, and more. Tools that will see extensive moving forward.

The ever evolving workspace at Driftopia HQ
The ever-evolving workspace. The wall keeps the elements out while I work on the roll cage fabrication. The shelf along the wall works great for all of the extra tooling.

Roll Cage Mount Plates

The roll cage mount plates connect the roll cage to the car’s chassis. Traditionally, the plates and mounts attach to the floor pan. However, the exo car’s lack of body panels and a roof opens up many different mounting possibilities. In this case, the vehicle will see extensive track use and potential endurance use, so I want to accommodate various driver sizes.

To do this, I am mounting the main roll hoop on the area behind the driver on the horizontal plane above the floor pan. The main hoop will also reach slightly above the factory roof line. This allows a larger containment seat installation—something rather tricky in a standard Spec Miata or any Miata racecar, for that matter.

The door bars will also mount to the door seam, further increasing the driver room.

Constructing the Roll Cage Floor Plates

Floor plates are constructed from 1/8″ to 3/16″ plate steel. Starting at the back of the car, I first made the rear strut tower plates. There will be bars on each side of the chassis that triangulate the rear strut mount to the main roll hoop. These were the most complicated plates to construct as well. So, to get it right the first time, I used a piece of cardboard to cut a plate template. Then transferring the template to the metal.

Cardboard template used to approximate the rear roll cage mounting plate on the exo car 'ghettocet' miata.
The rough cardboard template for the left-side rear strut roll cage plate is here. Flipping it over for the right-side template.
Steel plate for the rear strut mounting plate cut out and ready to be welded.
It’s always nice when things fit the first time. With a bit of surface prep, the rear plate will be ready to weld in place.
The rear roll cage mounting plate welded to the strut top area of the miata.
Here is the result after welding with the problematic 20-year-old Lincoln Electric machine. This plate also nicely reinforces the strut top.

The rest of the floor plates were easy. Mainly consisting of square or rectangular pieces. Pushing the main roll hoop mounts out as far as possible for maximum space. I can’t think of what to name this area for the life of me, but the pics below show the location.

Main roll hoop location for the mounting plate on the exo car 'ghettocet' Miata.
The location for the main roll hoop mounting plate after prep. I ground the seams a bit so they are level with the weld. This will add strength to the mount.
Main roll hoop mounting plate welded and installed on the exo car 'ghettocet' miata.
The main hoop mounting plate.

Once again, to maximize the interior room, the forward bars will be mounted just behind the A-pillar on the door seam instead of inside the pillar on the floor. This area has a slight curve, so I bent the plates slightly to ensure a tight fit.

The forward a-pillar bar mount plate on the exo car 'ghettocet' miata.
Pictured is the forward a-pillar bar mount and one of the four door-bar side impact mounts I added. The side points aren’t a requirement per the rules but are something I am used to having on my racecars.

Of course, there is a time lapse of this process, and this one is a bit longer. Wearing long sleeves in the summer heat of the Southeast is brutal, causing me to take several breaks throughout the day.

Next Steps

Now, it is time to bend some tubing and weld the cage together. There are a few considerations, as I want to tie the front strut mounts to the cage as well. But in the meantime, the main cage attachment points are set, and it is time to move forward.

The test weld tree I built to dial in the lincoln electric welder.
For fun, here is the weld ‘tree’ I built to familiarize myself with the welder again. I was eventually happy with the results, but the 20-year-old welder sometimes has a mind of its own. I am using it to finish this project and then upgrade.

By Chris Simmons


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