heinzboehmer's 2002 Topaz 6MT Coupe

[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.

[heinzboehmer]

Well, more than a year later and finally got around to finishing up my rear seat weight reduction project. Left off here:

Parts/tools ordered for V2.

Here's the V2 attempt that I tested out on the spare set of seats I took apart:





This worked okay, but it was pretty tricky to get even tension on the seat cover and required it to be permanently modified. So instead, I decided to ditch the Victorian age inspired approach and instead draw inspiration from the RC community.

I came up with this, a 3D printed structure reinforced with carbon fiber tubes, that is made to mimic the original steel frame:



I'm still a pretty big CAD noob, so making this honestly took forever. Fortunately the bigger seat is just a stretched mirror image of the smaller one, so that saved me a good chunk of time. Still, spent way more time on this project than originally expected (what a surprise).

Anyway, to ensure the plastic parts wouldn't break when assembling, I split it up into multiple pieces (which was needed anyway, as the whole thing exceeded the build volume of my printer anyway) so that I could print them all upright:




Yes, the amount of supports is kinda crazy, but this was unavoidable thanks to the print orientation I chose.

Printing everything standing up makes the lip that the leather hooks onto pretty strong, but also makes the structure fairly weak on its long side, hence the CF reinforcements:



I made the sleeves fairly tight around the tubes, but to make sure they wouldn't move, I modeled some clamps/notches into the sleeves where the tubes ended. This allows for the use of a couple small screws to clamp the plastic around the tubes. Here's a cross section showing that off (you can also see a bit of the keys I modeled into the lip that the leather attaches to):



First test prints:




Looking good, so I fired up the print factory and started cutting the tubes. Here's all the pieces needed for the right frame:



Assembled and installed for a test fit:






Super happy with how it came out, looks pretty much indistinguishable from stock.

[heinzboehmer]

Shoot Mark @ Driftec a message. He's super easy to get ahold of, I installed one of his hand brake kits and we chatted a couple times about the install. Nice guy.

Good to know, I'll reach out.

Skimmed through the install instructions for the handbrake kit and it seems very well thought out. Gives me a bit more confidence in the RTAB bracket.

[George Hill]

Shoot Mark @ Driftec a message. He's super easy to get ahold of, I installed one of his hand brake kits and we chatted a couple times about the install. Nice guy.

[heinzboehmer]

Is the toe adjustment range an issue?

Yeah, at my current ride height (higher than most track cars), I can't get less than 3/32" toe in at -2 deg camber in the rear. I could go lower and get more sensible toe at higher neg camber, but I was hoping to go back to stock height instead, so those brackets are probably my only option.

[bigjae46]

Oh also, came across this product that should allow me to run the rear toe + camber I want at a higher ride height: https://drifttec.co/products/high-to...ets-e36-e46-z4

I'm still undecided on them though. My biggest concern is binding, since there has to be a lot less clearance from the bracket to the bushing to allow for the extra toe adjustment. This image shows the difference in geometry pretty clearly:


I'll likely just leave it alone for now and reevaluate when I change springs/dampers/get an alignment.

Is the toe adjustment range an issue?

[bigjae46]

How are you securing the line from banging around?

I just let it dangle but you could zip tie it. Or use a bulkhead fitting and fab a bracket that is welded or bolted to the frame rail. In fact...I might end up doing that!

[heinzboehmer]

Oh also, came across this product that should allow me to run the rear toe + camber I want at a higher ride height: https://drifttec.co/products/high-to...ets-e36-e46-z4

I'm still undecided on them though. My biggest concern is binding, since there has to be a lot less clearance from the bracket to the bushing to allow for the extra toe adjustment. This image shows the difference in geometry pretty clearly:


I'll likely just leave it alone for now and reevaluate when I change springs/dampers/get an alignment.

[heinzboehmer]

Was pretty hot here yesterday, so took that as an opportunity to torture my car's cooling system on the highway and grab some data with the new rad. Ambient temps were ~40C and AC was on full blast.

Did my best to go WOT wherever I could to really stress the engine. Was able to get it hot by doing one of two things:

1. WOT at 2.5k-3k rpm in sixth going up a hill
2. WOT from 5k to 8k in third, then engine brake back down to 5k and repeat ad nauseam

Here's the data with a couple interesting points highlighted:



Was seeing 5-10C across the rad, which seems totally acceptable given the conditions. Think the most important part is that this drop was consistent, regardless of whether I was cruising or really beating on it. Sounds like the car is ready for another hot track day stress test.

Here's the full data if anyone is interested: https://datazap.me/u/heinzboehmer/ho...y-new-radiator

[heinzboehmer]

How are you securing the line from banging around?

Racecar grade zip ties is my guess

[Slideways]

IIRC, Its an M12 banjo bolt with a -6an male connection. Then a length of -6AN hose and a male thread -6AN plug. IIRC, I had to remove the VANOS pressure canister to get the banjo bolt in.

How are you securing the line from banging around?

[bigjae46]

That's a pretty great idea. What fitting did you use?

IIRC, Its an M12 banjo bolt with a -6an male connection. Then a length of -6AN hose and a male thread -6AN plug. IIRC, I had to remove the VANOS pressure canister to get the banjo bolt in.