Black & Tan 332iT

[Bry5on]

So I finally finished my project of modeling the roll centers at each end of the car, along with the roll axis and CG so I can calculate total roll and correctly set my front/rear roll couples for steady state handling. For the setup I've modeled, I'm on stock e46 M3 springs with flipped front camber plates and maxed out rear lower control arm negative camber. I've also got Turner RACP plates which drop the subframe by I think 1/8".

As you'll see below in the following images, the e46 has a pretty steep roll axis curve. What this gives the car, is natural stabilizing tendencies on dynamic corner and throttle changes, and a tendency to provide front end grip on steering input changes (contrast to a 911 which is a bit different/backwards). The way to think about roll couple geometries is all about dynamic transitions. When your car is going through an instantaneous change to steering/cornering load, your suspension takes time to settle into its steady state. At initial steering input, your roll stiffness comes from your suspension geometry, rather than your springs and sway bars. As you settle into the corner, your damper settings control the transition of load from your initial suspension geometry loads, to your steady state spring/roll bar driven loads.

I'm over-generalizing a bit, but the skinny is that the roll axis is very important for dynamic transitions, and is also extremely important for calculating ideal roll couples (FRC or Front Roll Couple) in that wonderful FCM Ride Harmony spreadsheet.

I measured my car, an M3 converted wagon with 48.5/51.5 F/R weight bias, to have a CG at 540mm, a front roll center height of 39mm, and a rear roll center height of 284mm. This means that the roll moment arm for the front suspension is 501mm and the rear suspension is 256mm. In other words, the front roll moment is 1.96x the rear one. Using these numbers, we can now calculate the ideal steady-state roll couple for my car on square tires, with the untrue-but-generally-practical assumption that the roll center does not move from here. What's the answer? A Front Roll Couple of ~66% is the theoretically balanced steady-state chassis that will yield maximum corner holding. This is impractical for most folks, as a perfectly balanced car can feel skittish when on the power, and will not tend to understeer at the limit for safety, among other reasons.

Now that the weather has gotten a bit more dry, I've noticed that my car does indeed have a tendency to understeer at the limit with my current FRC of 71.5% - I'll be installing the CSL rear bar I have to bring this down to an FRC of 69.9% to see how that does. Wish me luck!

edit: Also note, that the more you lower the front of the car relative to the rear, the higher your FRC needs to be to compensate!

Full Model isometric view


Front Model



Rear Model



Side/Axis Model



Roll couple numbers

[Bry5on]

Today was a long day under the car, not a lot of pictures but a fellow local e46 friend @tflow (tagging never seems to work with you man) came by to lend me a hand with this one. Thank you! The list of things done today:

• Installed rebuilt 3.62:1 wavetrac diff, REM polished gears from diffsonline
• Replaced my brand damn new rear lower control arms with ECS adjustable ones
• Replaced rear sway bushings and links
• Replaced the lower shift pivot. I hate that thing.
• Replaced inner half shaft CV joints
• Replaced driveshaft rear CV joint
• Dropped the subframe and drilled and tapped the holes for the upcoming vincebar

I once again chickened out on doing solid subframe bushings. I decided at the last minute to keep the urethane ones that are in there as I really didn’t want to re-do that job if I got some diff whine. Anyone want some almost-new rear lower control arms, some new ground control lower control arms, or new bimmerworld solid subframe bushings?

The rear feels normal now, like a regular car without any issues, easy to shift smoothly. Even new many of the e46 M3s had enough lash in the diff that they felt like something was wrong, and this one feels better than my long time ago almost new e46 M3 did. I could also swear that it’s quieter under normal driving and I’m 100% certain that it’s quieter under limited-slip action. So far so good.

I also pinched the steering rack boots to feel for indication of leaks past the seals. No leaks yet, so the rack rebuild continues on strong!
The car really feels great, I’m looking forward to the chassis work to stiffen it up and bring in some of that e39 rigidity feeling. Once the Slon brace, vincebar and v-brace are in, this’ll be an objectively better car than any of the ones out of the factory way back when.

[Seano666]

Good lord, I need that carbon brace in my life!

[heinzboehmer]

The airbox is very certainly much louder at WOT, but low loads sound imperceptibly similar to me. You can hear a heavy throttle blip a bit more than before, but I don’t think any of this is a bad thing. It sounds rowdy only when you’re rowdily on the throttle.

That actually kinda sounds awesome. More noise but only when you want it. This brace is becoming more and more tempting

[Bry5on]

Well it’s not yet bonded in, but I did assemble most pieces in situ and check hood clearance with play-doh. The Slon brace is in the same place as the factory brace, so I nipped off 1/4” of the non-m hood brace and hit the exposed metal with a coat of paint. The brace and filter housing are currently installed and working.

The airbox is very certainly much louder at WOT, but low loads sound imperceptibly similar to me. You can hear a heavy throttle blip a bit more than before, but I don’t think any of this is a bad thing. It sounds rowdy only when you’re rowdily on the throttle.

Fitment isn’t OEM good, but it’s impressive for a v1 of an aftermarket part that does this much. I did have to swap the left and rightmost air filter housing bolts with some fully threaded T30 bolts that I had lying around from Tesla battery modules. Slon provides spacers because the partially threaded factory ones would have shanked out. I preferred to eliminate the spacers and just use different fasteners.

The vacuum line at the top of the airbox needs to be deformed as it routes directly through the bar. I used a hot air soldering iron setup and this made quick work of rerouting the hose, in a way that shouldn’t cause problems without the bar.

Tape is on the bar to make sure I see any evidence of the hood impacting it before it starts to cut into any carbon or epoxy. Lots of pics:

[Bry5on]

So the Slon brace is pretty clever in the way it spreads load without putting the carbon in compression. I'll share a few pictures in a minute here.

Some brief mocking up and measuring shows that this'll be a real close fit to the non-m hood. I already have a little bit of interference to a formed flange supporting the hood to the stock strut bar, which is fine with aluminum, but the carbon would wear through and this could cause a failure. The M3 has more clearance here due to the different hood design, so I might need to get creative. The strut slots look a bit longer than the stock ones, which is good, because this bar needs to be removed as one piece and the studs are at an angle, not vertical, so the slots will provide appropriate clearance here.

The carbon filter housing is incredibly light, it doesn't damp knuckle noise as well as the stock pieces. I'll be paying close attention to whether or not this adds too much noise into the cabin, with the concern being particularly lifters and valve train at low loads. I can always add sound insulation to this later.

There is a little bit of an air gap (<1/4" x 6" long) at the firewall to air filter housing interface where the strut brace attaches. My current plan is to fill this with Butyl to avoid pulling hot unfiltered air into the cabin.

Here's how it all goes together, as I know many folks are curious (as was I):
Carbon piece gets bonded to become the windshield support, firewall insert fits over two square bosses on the windshield support:


Strut brace to support adapter sits directly on the bosses in the windshield support:


Filter housing goes on top of Strut brace support adapter, two square washer/bosses fit through holes in the filter housing, two fasteners go through this whole stack. None of the carbon pieces are in compression:



Getting my hood height measurement datum set:

[Bry5on]

Ha, that level of mud... been there done that. Question is - how do you clean yourself off after, I guess there's probably a washroom nearby? Or get in the back of the wagon and use that as the changing room 🤣? I went to a gravel race with a friend and it was held after a lot of rain - we had a similar level of mud, the interior of his car got kinda dirty but he doesn't care and we used Lysol wipes to clean it after.

Ha! You know the struggle. I always bring a change of clothes and I’m just not shy about parking lot changing. Anything to keep that leather nice and smooth!

[timmo]

Ha, that level of mud... been there done that. Question is - how do you clean yourself off after, I guess there's probably a washroom nearby? Or get in the back of the wagon and use that as the changing room 🤣? I went to a gravel race with a friend and it was held after a lot of rain - we had a similar level of mud, the interior of his car got kinda dirty but he doesn't care and we used Lysol wipes to clean it after.

[Bry5on]

I managed to coax a couple family members in town to help me install the shadowline trim today. Looks good!


while we were doing that, another package showed up..

[Bry5on]

A couple big things arrived in the mail today, looking like something good will get done this weekend

1) Full set of shadowline touring trim, doors and window frames, from German eBay
2) The wavetrac diff

Along with the diff, I’ll be doing:
1) ECS lower adjustable control arms for the adjustment range. I chickened out on the ball joint option due to 2)
2) Solid subframe bushings (fingers crossed)
3) Drilling & tapping holes for the vincebar
4) Driveshaft & halfshaft CV joints
5) Sway bar bushings

At that point, I’ll be down to just six more things:
1) Slon strut stiffening brace
2) vincebar
3) M3 subframe v-brace
4) black headliner upholstering
5) machining the adapter for the stealth hitches 2” hitch and installing
6) OEM M3 washer fluid reservoir setup

Going to be a nice setup!

Diff still boxed away:

Weekend duty from last Sunday:

Oh, and I nerded out with the correct coolant reservoir clamp and clamp cover, along with new harness and coolant line clips along the core support:

[Bry5on]

The rebuilt 712 steering rack went in this afternoon, so far so good, no evidence of leaks. There was some noticeable play on the pinion of the M3 rack I removed and zero play on the 712 I rebuilt that went in. I’d say the more noticeable thing (having already had a 712 in previously that leaked) than the ratio change was how precise the rack is after the rebuild. I’d certainly recommend doing this to anyone who’s noticing some vagueness on center or with mid-corner corrections. The rebuilt rack solved that for me.



While I was in there, I finally cleaned all the grime off the shear plate and undertray. Much more pleasant.

[Bry5on]

The Hotchkis front sway bar showed up earlier this week. I didn't want to install it using the urethane bushings that come with it (if you can't tell by now, NVH matters to me and I hate urethane), and since it's only .5mm smaller than the CSL bar, I decided to chance the install with CSL rubber bushings. The OEM bushings use a 1mm diametrical interference, so the CSL bushings with Hotchkis bar have a .5mm diametrical interference. I installed them as-is with .5mm interference and the test drive felt totally normal. While I was in there, I put in the steel sway bar bushing clamp that the non-m and CSL use and dumped the M3 aluminum ones.

If you want to replicate this, and you're dead set on OEM 1mm interference, a ~1mm plate between the bushing and frame rail will deform the rubber to get you to an equivalent interference to stock.

I set it to the soft setting, which is 11% stiffer than the 27mm cabrio bar that I had in there previously (I ran the numbers, Hotchkis seems to be quoting stiffness differences from the 27mm cabrio bar, not the 26mm coupe bar). After the first test drive, it definitely feels firmer, with more confident turn-in and like there might even be more front end grip? I was expecting a little less front grip and more understeer bias. Either way, it feels good, and I don't think I'll be installing the rear CSL bar that I have here + setting the front to the medium setting. I'm pretty happy with where it is.

The Hotchkis bar, bushings and clamps come in at 4.2lb less than the 27mm cabrio bar, bushings and aluminum clamps that came out, which was a nice bonus surprise. Once I install the hitch, Slon brace and remove the roof rack, I'll be under 3400lb with 1/4 tank with no compromises. That brings me to the same weight as an e46 M3, but ~1% more rear biased B).

Some pictures of the bar in the bushing, and yes I'm redoing the leaky power steering lines and reservoir soon..

[0-60motorsports]

I’m using a kit made by Gates. It’s got everything including the little o-rings for the transfer pipes. I bought it a while ago, this looks like it: https://www.ecstuning.com/b-gates-pa...it/348654~gat/

Awesome Thanks.

[Bry5on]

Well it was rainy all day today, so that means house and car work. The 6001 bearing at the bottom of the pinion shaft didn't feel so great, so I finished off the rack rebuild other than replacing this bearing (which arrives this week). I didn't bother replacing the PTFE seals as I don't have tapered tools to stretch/install them properly. Yet another concession that I hope I don't regret down the road..





I also got to painting the ground control lower control arm replacements. I haven't been able to get camber in spec on either side (maxing under 1.6 degrees on both sides), and I figured I'd try a set of arms with a ball joint a la CSL. The ground control arms are a nice shade of red, but I'm not exactly jazzed about having some red arms showing from underneath my car as folks follow me. It just screams 90's Honda Civic to me. I also found it a bit odd that the two arms are using what appear to be different brand ball joints.

[Bry5on]

That's great. Where did you get parts to rebuild the steering rack?


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I’m using a kit made by Gates. It’s got everything including the little o-rings for the transfer pipes. I bought it a while ago, this looks like it: https://www.ecstuning.com/b-gates-pa...it/348654~gat/