heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Alright flimsy racecar seat backs made a couple things very obvious.

First up, the way I had attached my plywood barrier was fine for stopping sharp objects from cracking the carbon wall, but not for actually stopping heavy objects from entering the cabin.

I wanted to attach it to as many stock structural points as possible, but with the seat latches gone, I had nowhere to attach the barrier latches. Dug through the stash and found a couple nuts that fit the stock seat latch bolts:



The captive nuts in the seat latches aren't in line with each other, so I was only able to get one bolt through my latches. Decided to add a couple rivets to keep them from rotating:




I would have preferred to use both bolts, but these top latches aren't what's gonna be seeing most of the load in a crash, so it should be fine. What will be seeing significant load are the bottom two points that attach to the frame tie down brackets:



I had previously used wood eye screws for this. They would have 100% ripped out under any significant load, but I was fine with that cause the stock seat backs were still in place. That is no longer the case, so I got some proper bolt through eye bolts and big fender washers:



Did a similar thing up top:



First issue fixed, onto the next one.

The Slon wall has acted as a giant speaker that amplifies all the annoying noises/vibrations that get to the the rear subframe/RACP since I installed it. However, the seat foam absorbs the majority of that, so hasn't really been a problem. Turns out the stock seat backs were contributing to the attenuation and absorbing a very specific resonance from the panel as well. Poked around and found that if I put pressure on two specific points on the panel, I was able to get rid of the resonance completely.

Following video shows my testing for this. I'm hitting the panel with my fist where the green circle is and am placing one finger with very light pressure where the red x is:

Headphones encouraged, but you can hear the resonance right at 201 Hz. You can even clearly see it in the waveform of the audio in that video. Notice how much longer the decay of each hit is when I'm not damping the left/right sides with my finger:



Printed some modified sections for my seat backs and added some adhesive window foam seal to put some pressure on the panel at the two dampening points that I identified:





Resonance is gone! I'm so glad this was an easy fix, it was driving me crazy on the highway. If you want to feel my pain, type 201 Hz into this website and just let it play for a while: https://www.szynalski.com/tone-generator/

That's what I had to listen to constantly whenever I went above 60ish mph. So glad it's gone.

[heinzboehmer]

Thanks! I also don't love the "regular" back seat deletes, the NVH increase is crazy.

And yeah I would absolutely not do this if your kid rides in the back regularly

[Obioban]

I like it! THIS is my kind of back seat delete.

I'd love to do similar, but ues the back seat routinely for my child, so...

[heinzboehmer]

Also, feel the need to reiterate this in case anyone wants to replicate the project: This is pretty sketch.

The stock seat backs are chunky because they play a big role in keeping the rear passengers safe in a crash. They both prevent stuff from flying into the cabin from the trunk and they also prevent passengers from going into the trunk if you get rear ended.

No one has ridden in the back of my car in the last few years (and they won't in the future because of the lack of seat belts) and the Slon wall + plywood barrier help protect against stuff flying into the cabin. Without all of this, I wouldn't feel comfortable with this mod.

Okay, onto weights. Here's the weight of everything that came out:

• Stock left seat back: 15.3 lbs
• Stock right seat back: 8.7 lbs
• Armrest frame: 1.9 lbs
• Armrest back flap: < 0.1 lbs
• Middle belt: 0.6 lbs
• Seat back latches: 1.8 lbs

(Note that the left and right seat back weights are different to what I measured before. I think that's because the others had the ski pass through. There's still only a 0.2 lbs difference between both sets, so close enough.)

And here's everything that went in:

• My left seat back: 1.5 lbs
• My right seat back: 0.9 lbs

So, 28.3 lbs came out and 2.4 lbs went in, giving a net weight savings of 25.9 lbs, nice.

[heinzboehmer]

Here's all the parts needed for the other side:



Mostly assembled:



Here's some closeups of the clamps:





Since this side also has the armrest, the stock metal frame has some tabs for the leather that goes along the perimeter of the armrest. I originally planned to print some hooks that would slip onto the carbon tubes, but then completely forgot about those and put a bunch of clamps all around that would interfere with them. Sooo zip ties to the rescue:



Speaking of the armrest, I had already ripped out the foam from the spare set of seats, so I disassembled the armrest that came out of my car and reassembled it with just the foam. I also seam ripped the flap that's attached to the back of the armest because racecar or whatever:




To mount the frames to the car, I modeled a pin that goes into the chassis just like stock:



For the middle pivot point, I made a cap for the carbon tube that can fit the stock plastic bushing:






For the top, I modeled some tabs into the frame that I stuck some velcro on. A corresponding piece of velcro went on the Slon wall. The tabs can kinda be seen here:



Frames up:



And same pics, but with the foam and leather installed:




Armrest got attached with some more velcro. There's two bits along the top and bottom sides and a bigger one that goes to the X clamp directly behind the armrest:



Latches were no longer needed so those came out:



I wanted to keep the receptacles for the rear three point belts cause I use them for my harnesses, but was sketched out about modifying the metal mounting hoops, so decided to just cut the middle belt out:



And that's about it! I'll post the final weight breakdown in a bit, but I ended up removing roughly 25 lbs with all of this, pretty pleased with that.