Fitting an Elephant in a Suitcase: a DIY on mounting race seats to the floor

16944 Views 18 Replies 13 Participants Last post by  Mehata
To start off I'm 6'4" and close to 200 lbs, most people laugh when they see me get in/out of my car. For the last 8 months or so that I've owned my car I have been trying to make it more tall-friendly. Hell, everyone sees it as a small car, so I feel like a lot of people could benefit from this write up. I originally ordered a set of KazeSpec PCI seat mounts ( They lined up perfectly with the existing seat mount holes and allowed for a clean and easy install. However, I'm a tall, long-torsoed guy so this is where things got tricky. For this install I was using the Corbeau FX1 Pro in micro-suede. When mounted as low as possible on the PCI mounts, the left shoulder bolster contacted the door panel badly, when mounted high enough to clear the door panel I was crammed into the cockpit and couldn't even keep my head straight up. So the time came for something creative and absolutely necessary...

Disclaimer: I am not responsible for any damage done to your car, yourself, or others. All this is done at your own risk I am not an expert just an enthusiast.

So at this point I had two issues:
1) Getting low enough to clear my roll bar
2) Getting the seat bolster to clear the door panel

The PCI mounts got me as low as possible by using the stock seat mounts there's no doubt about it, so it was out with the old:

Using a combination of Dremel cutting wheels and crow bars I was able to pop them off. This allows for a flat install of the seat side mounts it also allows me to mount the seat as far back as possible allowing for the shoulder bolster to clear the door panel.

The FX1 Pro has the option of side-mounts or bottom-mounts. The bottom mounts include four small pedestals at each corner to aid it mounting it, however these 1" protrusions would add 1" in ultimate height of seat mount. So out came the saw and I took off those pesky little suckers! Note: I only saw it necessary to remove the rears as I wanted a slight layback to the seat thus also increasing the geometric distance to the roof of the car/top of the rollbar.

There we go, 1" closer to my goal of LOW. Next up I fabbed up some backing plates to mount under the car to hold my side mounts in. I took 1/8" steel in a 2"x48" segment and cut 1.5' sections. I used the side mount brackets supplied with my PCI mount but you can easily fab up your own.

I matched up the side mount brackets to the steel flat stock and marked where I wanted the holes to line up.

At this point I took the now drilled flat stock and lied it inside the now gutted floor-pan and marked the holes with a permanent marker. Note the arrows pointing to the black dots, the X-d out dots were mismeasured, make sure that not only are the dots spaced appropriately front to back but also side to side, last thing you want is brackets mounted too narrow.

Now drill those suckers out! the floor pan isnt that thick, which makes this seem like a sketchy operation, but with the backing plates all should be sound in the event of an accident.

Now replace the carpet, locate the holes in the floor board and punch holes through the carpet. Now place a grade 8 bolt through a grade 8 washer then through the sidemount and finally the floor board. Repeat this for the other side's. Now jack the car up, locate the bolts sticking out of the car and match the backing plates up and thread the grade 8 nut onto the bolt. You might need to dremel and hammer some heat shield out of the way.

There we go both sides finished, torque down those bolts and look over everything! at this point i also took the time to drill a mount for my harness. Now this is where backing plates become absolutely important. I chose to drill the inside mount through the transmission tunnel near the rear o2 sensor pass-through (as you can see the previous owner destroyed the o2 sensor some how)

I used the biggest bolt that i could pass through my harness mounting hardware all grade 10 hardware. The quality of the hardware used for mounting seat belts is very important this isnt a place to cheap out. The outside mount i used the stock seat belt mounting hole. After drilling the hole through the transmission tunnel (keeping in mind you want both sides to be even to maintain an even load from the belts on your hips in the event of an accident) Taking the harness mounting bolt, thread it through the transmission tunnel, and then using the largest washer you can find, torque down that grade 10 hardware nice and tight.

The top belts of my harness wrap around my harness bar and a secured safely with the supplied mounting hardware. The 5th and 6pt will be mounted similarly to the 4th point at a later date.

The seat now gives me enough head room to nearly pass the broom stick test, I feel much safer driving now. The shoulder bolster clears the door panel perfectly tucking behind it. I have tons of leg room now and nearly have to stretch my legs out to reach the pedals. :lol: Well anyways, this is the way I squeezed every last bit of room out of my little Miata interior. I'm open to any conversation or critiques on my technique. This is really the deepest Ive gotten into my miata without having a write up to follow so I figured I'd provide others with a guide!

Look forward to hearing your thoughts and comments guys.

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Nice write up, I took an identical approach for the seat rails, but used 1/4" steel bar instead. 2 drill bits later, and I had some sweet rails that are probably stronger than any aftermarket rail.
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