heinzboehmer's 2002 Topaz 6MT Coupe

[Obioban]

Honestly, the stock suspension feels pretty firm after all the chassis stiffening. Pretty wild. But the car can finally accept more spring rate and still control the body, which I didn’t think it did a great job at before with aftermarket/stiffer springs personally. I actually went from aftermarket -> stock!

My aftermarket setups have gotten softer and higher every time I've changed setups!

[Bry5on]

Didn't realize your (plural) suspensions were so stock. Since I'm 19 years into various aftermarket suspensions, I sort of consider them... stock? standard? not sure what the word is, but stock didn't occur to me as a possibility 🤣

... Carbon roof was my least favorite DIY project I've ever done.

Honestly, the stock suspension feels pretty firm after all the chassis stiffening. Pretty wild. But the car can finally accept more spring rate and still control the body, which I didn’t think it did a great job at before with aftermarket/stiffer springs personally. I actually went from aftermarket -> stock!

[Obioban]

I had a similar conclusion to Heinz. It feels like the car ‘wants’ more spring now. It’s definitely working the springs harder and you can feel it. It’s also better damped. In mine, I’m able to push it to its g-limit much more consistently now and since I’m on stock springs (and he’s a little lowered/stiffer) we’re probably both using the bump stops too regularly in hard corners.

The carbon roof is worth a 4% body roll reduction on a 3400lb e46, which is roughly an equivalent change to an 8% stiffer spring. In conclusion, I think carbon roofs are the correct next steps.

Didn't realize your (plural) suspensions were so stock. Since I'm 19 years into various aftermarket suspensions, I sort of consider them... stock? standard? not sure what the word is, but stock didn't occur to me as a possibility 🤣

... Carbon roof was my least favorite DIY project I've ever done.

[Bry5on]

Awesome! Chassis stiffness is the second best mod after lightness

... I am surprised you're thinking stiffer springs as a result. IIRC conventional wisdom is that a stiff chassis lets you get away with softer springs, all else equal (and soft springs = more grip).

I had a similar conclusion to Heinz. It feels like the car ‘wants’ more spring now. It’s definitely working the springs harder and you can feel it. It’s also better damped. In mine, I’m able to push it to its g-limit much more consistently now and since I’m on stock springs (and he’s a little lowered/stiffer) we’re probably both using the bump stops too regularly in hard corners.

The carbon roof is worth a 4% body roll reduction on a 3400lb e46, which is roughly an equivalent change to an 8% stiffer spring. In conclusion, I think carbon roofs are the correct next steps.

[discoelk]

Strut bar is really cool. Are you planning on using the OEM cabin filter?

[Obioban]

Awesome! Chassis stiffness is the second best mod after lightness

... I am surprised you're thinking stiffer springs as a result. IIRC conventional wisdom is that a stiff chassis lets you get away with softer springs, all else equal (and soft springs = more grip).

[heinzboehmer]

Do your threads have a radius on the outer ridge? Those BMW nuts are designed for rolled thread fasteners, so if your studs have cut thread fasteners, you could be fighting that.

They do not, I think you're right on the money with this one.

Hell, you could also just print it out of PPA or something rated above 150C or so with a 'closed cell' inner support structure for thermal insulation. I think the factory parts are fiberglass filled nylon (eg: PPA-GF). That's a 3D print for the win situation.

Factory parts are both stamped UP-GF, so very similar. Interesting idea about the using the infill as thermal insulation! I'll have to mess around with that.

Ideally, I'd like to make these parts much lighter than the stock ones, since I'm going through the trouble of remaking them entirely. Will have to see what the weights end up at before making a material choice.

Thats awesome news! I would love to do that to the car one day.

I'll share the designs for everything once I've sorted out all the small details!

[0-60motorsports]

Thats awesome news! I would love to do that to the car one day.

[Bry5on]

Do your threads have a radius on the outer ridge? Those BMW nuts are designed for rolled thread fasteners, so if your studs have cut thread fasteners, you could be fighting that.

On the cork insulation topic - you can apply the cork or other insulation of choice (zotek peel and stick foam is phenomenal...) to the engine bay side of the HVAC housing which would allow you to print it. Hell, you could also just print it out of PPA or something rated above 150C or so with a 'closed cell' inner support structure for thermal insulation. I think the factory parts are fiberglass filled nylon (eg: PPA-GF). That's a 3D print for the win situation.

[heinzboehmer]

Congratulations man - you must be so stoked with how this has turned out!!! It's been awesome following along and seeing you bring this together. Very, very cool.

Man, you have no idea. I'm so happy with how this turned out. Took me forever cause I didn't know what I was doing, but the end result is so worth it.



Have a bit more seat time now and all of the above is still true. It's hilarious how much more capable the chassis feels now. I think what has most surprised me is the throttle steer thing. I wasn't expecting it to be this noticeable. You can give it throttle mid corner and it keeps turning, whereas the front would just kinda wash out before. It feels like it has SO much more grip.

Have a track day coming up in a couple weeks, so will really put these things to the test then. Gotta hurry up with the HVAC plastics though. Still lots of CAD ahead of me...

Also, one thing I forgot to mention earlier is that the stock BMW nuts for both the E86 braces and the E46 strut bar do not like my studs. The nuts are oval shaped so they don't back out, but they're meant to be used on fairly short studs. With these longer ones, the top threads start to get mangled as you thread the nut in. For now, I just ran a tap through all the nuts so that the threads are no longer oval. I likely need a better solution though, as the nuts under the windshield are facing the floor and could potentially back out. Cut down the studs? Get some nyloc nuts? Not sure yet, have to give it more thought.

[karter16]

Congratulations man - you must be so stoked with how this has turned out!!! It's been awesome following along and seeing you bring this together. Very, very cool.

[heinzboehmer]

So I went through the trouble of adding fast charging to the Gauge.S ashtray housing because I knew it would come in handy at some point. Even though I don't really ever use it (my phone usually sits on the wireless charger), it's nice to have the option of plugging it in, especially when using it for navigation.

The couple times I have wanted to use it, I've been unable to because the board overheats and shuts off. Stuck a couple heatsinks on top of the ICs and it seems to have fixed the issue:



Previously, those capacitors were bent downwards and attached to the ICs with some double sided thermal tape. Interesting thermal management strategy...

Oh also this



Took the car back up to scenic spot for the first test drive with the braces installed. Driving impressions in a bit, first gonna dive into how we got here.

As previously mentioned, I took the brackets down to TC Design for welding. Overkill, but they build racecars everyday (including that PT cruiser featured in this journal many pages back), so I knew the quality of work would be great.

Scribbles for Tony:




Studs pressed in and welded up! Tony was able to turn them around in a couple hours:





Hard to tell, but I had Tony tack all the studs to the brackets. I was able to press them in to where they don't back out, but they spin if you apply any meaningful torque to them. I think I might have made the holes for them a bit too big. Data sheet gives a range and I targeted the middle of it, but seems like I should have targeted the lower end. Lesson learned.

Actually, same thing happened with the windshield attachment point, even after putting it in a hydraulic press. For that one, I just roughed up the surfaces and added a bunch of the 3M 07333. This is absolutely not what it's meant for, but I just need it to counter hold the studs a bit until friction takes over. Worked like a charm:



I shouldn't have designed this piece for press in studs. Captive bolts would have been a better choice. If this adhesive bandaid fix ever fails, I think I can mimic the captive fastener thing with low profile hex head bolts and 3D printed inserts. Again, what's holding the bolts captive takes almost no load, so no need to go crazy with it.

Back to the strut tower brackets. As mentioned previously, I planned on bonding both parts for max stiffness.

Started by doing the last bit of grinding to match the profile of the stock parts perfectly. I also had to grind some clearance on the ID so that the stock plastic covers can clip in, completely forgot to design that it before having them laser cut. Then roughed everything up and prepped with acetone + IPA:



Of course, no project is complete without a huge fire hazard:



(stood next to this for the entire half hour they were in there with an extinguisher ready)

Bonding went super smoothly cause I was able to use the studs and fastener holes to clamp both pieces together.

And ready to drive!



I still need to give the brackets a final sand to smooth out any adhesive drips and get them painted, but they're good for now.

Onto driving impressions:

The car feels incredible! Exactly the same as how I remember Bry5on's car feeling when he first installed the Slon brace. Drove it back to back with and without the braces, just to make sure I wasn't making things up. Can confirm that there's a very tangible difference.

Front end is super eager to follow what your hands are telling it to do now. Makes it feel like the steering is quicker even though the ratio hasn't changed. It feels weird to not have to do any mid corner corrections, after driving the car for so long without this bracing. Now you can essentially just point it where you want it to go and it'll go there. I'd compare it to the difference when going from a grippy street tire (e.g. PS4S) to a 200tw track tire (on track of course).

I also noticed that I can steer the car with the throttle much more precisely in corners. Very much a welcome change.

A friend described the change super accurately: feels like the front wheels are pointing in the same direction now

Think this is the first time I've ever thought the car needs more spring rate. Feels like the suspension is getting left behind with the increase in chassis stiffness. Can't wait to get the Bryson braces installed for max stiffness gains. Then I'll go chasing suspension/CG adjustments.



P.S. HVAC plastics aren't ready yet, so they weren't installed for the test drive. The intake is LOUD with them out of the way, wow. Definitely gonna have to make my versions as thin as I can get away with. Think this will require carbon + some airy core (e.g cork, for thermal reasons), not printed plastics.

[heinzboehmer]

3M never got back to me about whether or not the 07333 will survive powder coating cure temps. Need to bug them again.

Just called 3M to ask and I was told the max temp this adhesive should be exposed to post-cure is 180 F. So right around the 80 C that the data sheet says not to exceed while curing.

Sounds like these parts are getting painted, not powder coated!

[bigjae46]

Wow! That looks slick!

[heinzboehmer]

Heinz, you can scan mine, and in the process scan the opening on the front so I can design my snorkel?

Thanks! I want to scan it in the M3 engine bay so that I can roughly copy the routing for my own version, so I'll probably just scan Slideways's car. Appreciate the offer though.

Down to scan you car for your snorkel whenever though! You know where to find me