heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Yeah, I actually chatted with SLON about this notion 3 years ago— if you are using the back seat as a seat, this is not a good idea. If you have heavy items in the trunk, not good in a crash.

100% agreed. I wouldn't be considering this if there was any chance of people riding in the back. However, the buckets make it so hard to get back there that the car effectively became a two seater when they got installed. I also made the decision to remove the rear seat belts a while back, which means the rear seats are completely off limits now and I don't expect that to change anytime soon.

Fortunately, this is easily reversible if I do ever change my mind.

Interesting idea.

I've been passively trying to figure out a rear seat delete option that doesn't look like crap. I never use the rear seats and if I had the Slon wall, I'd pull them. But I don't like an unfinished look in a street car, so something would have to go in its place that isn't a piece of plywood covered in carpet.

Yes, exactly! I knew there was a bunch of weight to be saved, but I don't like the look of any of the rear seat deletes.

I think this path is a good compromise between losing weight and keeping the factory looks and sound/heat insulation. I don't plan to touch the bottom section of the seats.

The safety stuff is the only bad part about all this, but I've probably talked about that enough.

[heinzboehmer]

Continued prototyping today. First I cut/ripped the armrest foam away from the armrest frame. Looks very ugly, but holds it shape surprisingly well. Will probably use this instead of some other foam now that I've seen what it looks like. Updated the weights in the previous post btw.




Then I stuffed the foam back into the armrest:




Pretty much indistinguishable from stock.

After that I reattached the leather onto the small seat back foam. Used zip ties because I didn't feel like messing around with the hog rings:



Then came tensioning the leather onto the foam. For this prototype, I just stuck a bunch of zip ties through the leather and foam. Worked pretty decently, but the shape isn't perfect:




I'll use a different tensioning solution for the final version, which should work better.

This did give me a pretty good idea of how it can be made to look, so I'm happy with that. Parts/tools ordered for V2.

And here's how both those pieces look in the car. Clearly not perfect, but I'm pretty confident that I can get V2 to look pretty much exactly the same as the stock seats.

[heinzboehmer]

Practiced my CAD skills today:



Then cut the same shape out of some 3/4" thick plywood:



The point of this thing is to act as an impact barrier for whatever I put in the trunk, especially to/from the track. It's not unlikely that I'll have some bigger/heavier stuff there (i.e. a small jack) and I really don't want that stuff to crack the carbon wall under braking.

Still need to figure out the attachment method. I have an idea that should make install a 10s job, but still need to try it out.

[Casa de Mesa]

Still need to figure out the attachment method. I have an idea that should make install a 10s job, but still need to try it out.

So I have this idea if yours doesn't pan out...

[heinzboehmer]

Lol that would probably take it from a 10s install to a 20m install

[heinzboehmer]

Finished the trunk partition.

Decided to make it a little nicer by wrapping it with some of the remaining materials I still had from when I made my seat cushion. First, wrapped in a couple pieces of the foam backed fabric. I used some spray adhesive to glue the flat part on and then some staples on the back:



Then wrapped it again with some leftover dinamica. Used same technique as before.

Back and front faces glued on:



Front overhang fabric wrapped around and stapled:




Yes I know my stapling job kinda sucks. It's pretty obvious that I have limited textile skills. Whatever, this thing is already way nicer than it needs to be, so I don't really care enough to redo it.

Then came the mounting solution. I used a pair of quick release hinges on the top and two eyelets with spring snap clips on the bottom. The hinges are attached to the chassis using the same bolts that hold the rear seatback latches in. For now, the bolts are running through the hinges and into the latches, but the latches will get replaced with nuts once I finish my rear seat lightening project.

Here's how to install this thing (mostly because I know I'll forget the steps in the future). First the passenger side clip gets clipped, then the driver's side and finally the whole thing gets pivoted up so that the hinges can latch into place. Removal is reverse of install:





Yes, I could have made this easier to install by placing the eyelets slightly lower in order to be able to clip the clips in after the hinges are latched in. However, I decided not to as I wanted to keep the clips slightly in tension to help reduce rattles and movement of the partition while driving. Clips also got some heat shrink tubing on them for rattle prevention. Might need to get some better rubber isolation for them though, as the heat shrink tubing does slide around a good amount.

Still only takes ~30s to install/remove, so I'm happy.

[heinzboehmer]

Track day tomorrow, so bunch of stuff got done this week.

First, I swapped the front bi xenon auto leveling sensor, as the original one cracked and the lever arm kept slipping out. Here's the old one:



New sensor and new lever arm installed:



Decided to swap out the lever arm as well because the control arm clip broke off a long time ago. Zip ties held up great though!



Unfortunately, the outside portion of the sensor connector crumbled when I went to reattach it, so I added some zip ties to keep it in place (visible above). Guess I just ended up swapping one set of zip ties for another.

Then I swapped out the turn signals, as the originals were falling apart.

Old:



(Note the deteriorated weather stripping and broken mounting tabs)

New:



Last came the new track wheels/tires and track pads. Wheels are ARC-8 in 17x9.5" ET35 up front and 17x10" ET25 in the rear. Tires are RE-71RS 255/40R-17 square. Yes, a bit of an unconventional setup with staggered wheels and squared tires, but I wanted to avoid spacers as much as possible.

I did quickly weigh this new setup vs my old track setup and it's significantly lighter. Should be fun on track. Here are the weights (per corner):

18" Style 67 RE-71R Front	48.7 lbs
17" ARC8 RE-71RS Front	43.6 lbs
18" Style 67 RE-71R Rear	53.7 lbs
17" ARC8 RE-71RS Rear	45.1 lbs

So total savings of 5.1 lbs per side up front and 8.6 lbs per side in the rear. Great!

Anyway, I knew I was going to need spacers to clear the front brakes, so I ordered a set of 5mm spacers. Here's what the clearance looked like with those:




It technically cleared, but there was <1mm between spoke and caliper, so I decided to step up to a 7.5 mm spacer.

Aah, muuuch better:




Here's what the car looks like dressed up in it's new track clothes:







And here's what the trunk looks like all packed up and with the partition in place. Even though the partition reduces trunk space a bit, everything still fits!

[Obioban]

7.5mm is a scary amount of spacer. I'd bump that up to a hubcentric 10mm.

... I'm thinking after I install my rear bulkhead, I may just hit it with some spray adhesive and put a superleggera pad of some sort on it for good.

Edit:
Actually, how close does it sit to the seat backs when installed? If it's right up against them, I'll probably just leave it alone-- I don't care if it gets visually scuffed up, just don't want it getting broken by something flying around in the trunk. If it's right up against the seat backs, probably minimal danger of that...

[repoman89]

7.5mm is a scary amount of spacer. I'd bump that up to a hubcentric 10mm.

Because of the limited contact with centering lip? From reading the Core4 Motorsports wheel mounting stuff, it doesn’t seem like the centering lip actually has any role in holding the wheel on. They write that the wheel is held in place by friction between the actual mating surfaces and the friction is maintained by clamping force from the lugs. Centering lip is just for centering. Makes sense to me, but I’m also going the route of eliminating spacers altogether for my track setup to avoid thinking about it.

[bigjae46]

I would recommend a tire OD of at least 25.5" and IIIRC a 255/40R17 is under 25" especially on higher speed tracks. A shorter OD results in a more RPMs for the tire at the same speed which adds a lot of heat into the tire. You run a much higher risk of overheating the tire which at best will force a cool down lap. I've found it causes the tire to wear out much quicker - in my case it was about 20% to 25% quicker. I essentially got one event less out of the tire.

I ran a 245/40R17 tire and they would get greasy after 4 laps. The gearing effect was nice.

[heinzboehmer]

7.5mm is a scary amount of spacer. I'd bump that up to a hubcentric 10mm.
... I'm thinking after I install my rear bulkhead, I may just hit it with some spray adhesive and put a superleggera pad of some sort on it for good.

Edit:
Actually, how close does it sit to the seat backs when installed? If it's right up against them, I'll probably just leave it alone-- I don't care if it gets visually scuffed up, just don't want it getting broken by something flying around in the trunk. If it's right up against the seat backs, probably minimal danger of that...

Oh! I forgot a picture!



I installed hub extenders even with just the 5mm spacer, so no sketchiness here.

And the wall does not butt up against the seat at all. There's a couple inches between them. I'll grab a picture later. But yeah, that's exactly why I built this partition.

Because of the limited contact with centering lip? From reading the Core4 Motorsports wheel mounting stuff, it doesn’t seem like the centering lip actually has any role in holding the wheel on. They write that the wheel is held in place by friction between the actual mating surfaces and the friction is maintained by clamping force from the lugs. Centering lip is just for centering. Makes sense to me, but I’m also going the route of eliminating spacers altogether for my track setup to avoid thinking about it.

I really wanted to stay away from spacers too, but also wanted to stay away from much lower offsets than stock, which is why I went for the ET35 wheel. Had I known that a 5mm spacer wasn't going to work, I would probably have just gone for the ET25 wheel to keep them square.

Oh well, I might swap the front wheels out when the tires are dead.

I would recommend a tire OD of at least 25.5" and IIIRC a 255/40R17 is under 25" especially on higher speed tracks. A shorter OD results in a more RPMs for the tire at the same speed which adds a lot of heat into the tire. You run a much higher risk of overheating the tire which at best will force a cool down lap. I've found it causes the tire to wear out much quicker - in my case it was about 20% to 25% quicker. I essentially got one event less out of the tire.

I ran a 245/40R17 tire and they would get greasy after 4 laps. The gearing effect was nice.

Interesting! I hadn't thought of that. Appreciate you sharing.

Looks like 255/40R17 is right over 25" and I didn't feel the tires overheating too much today, but what you're saying makes total sense. I'll keep it in mind for my next set of tires. Looks like I might be messing around with the setup anyway.

[bigjae46]

Interesting! I hadn't thought of that. Appreciate you sharing.

Looks like 255/40R17 is right over 25" and I didn't feel the tires overheating too much today, but what you're saying makes total sense. I'll keep it in mind for my next set of tires. Looks like I might be messing around with the setup anyway.

A 275 on a 10” wheel can fit with about -3.0
camber and fender mods. The lip just needs to be rolled flat which is pretty easy. Just need to be careful at the forward edge and the backside of the arch - might need to make a small relief cut in those spots to flatten the lip. It’s worth it.

[heinzboehmer]

Obioban here's what the gap between the seats and the wall looks like:

[heinzboehmer]

Been busy lately, so didn't have time to undo all the track stuff until recently.

Track day went great though. Cars feels amazing and is so much faster than me. Best lap was a 2:08 at Thunderhill East, which was 5 seconds faster than my previous best. Yeah it's not crazy fast, but I'm happy with it. Good friend of mine (who's a better driver) jumped into the car and put down a 2:07 first try with me in it. Clearly the car is capable of even faster laps.

The huge jump in time is partially due to all the changes to the car, but probably mostly due to the fact that I got an instructor for one of the sessions. Was great to have someone in there to point out all the bad habits I had developed. Felt so much more confident in my driving after that session and will definitely do it again if I get the chance.

The one complaint about the car I have is that it's a bit unstable under high speed braking. I changed too many variables to know for sure what caused it, but probable causes are the more rear biased 996 setup or my solid RTABs. I might swap the RTABs out for E89 rubber RTABs with limiters on the outside so that the car doesn't toe out under acceleration but does toe in under braking. It wasn't hugely unsettling though, so it's not a priority.

Anyway, grabbed a pic right before heading back home that I think turned out pretty good. That S2K is owned by that same friend who drove the M3 around:



First thing I did after the track day was to swap out the diff bushings. The slon wall acts as a speaker and made the poly bushing diff whine go from annoying to intolerable, especially after driving a total of 5ish hours on the highway.

I got some tools laser cut to press E36 bushings in without removing the diff. Basically just glorified washers and a thin wrench.



Started by removing the poly bushings, which wasn't too hard. Removed the aluminum insert with a big screw extractor and then just pushed the poly part out. Then used the different bolts to push the new bushing in. Was going great until the last mm or so. The E36 bushings are slightly shorter than the diff cover, so I made sure to make the press tool with a slightly smaller diameter to be able to get the bushing fully seated. Unfortunately, the press tool must have gone in crooked or something cause I heard a loud crack.

Sooo diff cover came out:





Bummer, but I was half expecting this to happen, so not too heartbroken. Brand new diff cover prepped and installed:





Opted for the liquid gasket instead of the paper because I wasn't confident that I would be able to get the diff side of the surface prepped well enough for that to not leak (since the diff case did not come out of the car). So far no leaks, but we'll see how it holds up to track abuse.

Since I had the diff cover off, I went in and measured backlash. I absolutely did not have the proper tool to do it with, but I managed to get a very repeatable measurement with my caliper. I stuck it to the diff with a magnet and used a wrench on the ring gear bolts to move things around:




I then used a similar technique to take backlash measurements of the spider gears through one of the cutouts in the carrier. This measurement was much less precise, but it told me what I needed to know. Here's what I measured:

Ring-pinion: 0.14 mm
Spider gears: 0.55 ± 0.03 mm

Note that the spider gear measurement is the lash between adjacent spider gears, so the total lash at the ring gear would be even more. Crazy how much play those things have. Left it alone for now, but something will need to be done about this diff in the future.


With the diff back together, I was able to do the rest of my track un-prep. Brake ducts removed, track pads swapped out and street wheels back on. The cause of my steering wheel vibration on the way back from the track became super obvious pretty quickly:




I always forget to do the aluminum tape after balancing the wheels. Will try my best to not forget before the next track day. Not a lot I can do about the rubber though

As a bonus post track surprise, I found a catastrophically failed front dust boot:



Hard to see in that picture, but it failed all the way around. Thing came out in two pieces. This was the only boot I found with a serious failure, but I did find a few others that were half melted. Replaced it with a girodisc boot for now and will likely replace the rest before the next track day. We'll see how those hold up.

Also, friend of mine recently bought a 3D scanner and said he'd be down to help me scan the car so I can design my V2 brake ducts. Those should help the boots last longer as well.

[heinzboehmer]

Some more pics from the track day:




About to launch off the bypass:



Aaand landed:



This last one is probably my favorite pic of the day. Was chasing my friend in the S2K down while he had a passenger in the car. Passenger had zero track experience, don't think he had ever really been in a fast car on the street. Guess my chasing was a bit too much for him, as they had to pull into the pits (one turn after where the pic was taken) to let the dude puke lol. Fun times.