Black & Tan 332iT

[Bry5on]

Well gents, I’ve finally got it. This morning, I did e89 Z4 RTABs with outer side limiters along with the 1mm larger CSL rear sway bar. Man, this is the hot ticket. I’ve finally got it right! That little bit of extra rear roll stiffness made all the difference. The car is more neutral and playful in corners now, super neutral and fast if you’re smooth, but it’ll still understeer on entry and oversteer on exit if you’re ham fisted/footed. Really nice to have that little bit of extra roll stiffness for the square tires on stock M3 springs, and it still has juuust a touch of understeer balance. The math says this should be keeping me off the bump stops and I’m inclined to agree. Just perfect, very happy over here.

What can I say about the Z4 RTABs? Well to my taste, they’re 75% of the precision of solid bushings, with the same NVH as stock bushings. No more rear end wiggling on throttle, but no NVH penalty. Really fantastic trade off as the rear is very well controlled again. The reason to go with Z4 bushings is all about how much rubber they have to press against the carrier (or limiter in my case). Otherwise they’re the same internal stiffness and geometry as stock e46 M3.

The bushings that came out of my car are near as new M3 parts, lemfoerder if memory serves, and had just a few thousand miles on them. You can see below that there’s plenty of evidence of the bushings toeing out all the way to the edge of the carrier. This calculates To almost a full degree of toe out. Hugely destabilizing! Again, these are new bushings! A solution to the rear end wiggling under throttle was required.


I used limiters from ECS for the outside of the Z4 bushings (half of the kit of four), which have a much bigger rubber lip on the outer side (toe out under throttle side). To fit the limiters, there’s just a minor trimming operation needed to make the limiter sit totally flush with the bushing. They then get installed all the way until the flanges touch the rear trailing arm. They get bottomed out, which looks a bit off, because the metal is not centered in the bushing like the e46 style, but this will place the bushing in the correct location.
By only installing outer limiters, this mitigates toe out under throttle while maintaining the factory designed toe in under braking for braking stability. I really wanted to keep that feature, and I’m happy to report that the results are great.
Other than that, install is totally normal. Make sure you set your toe correctly after or have the car realigned. Here are a bunch of pictures that might come in handy if you’re doing this yourself, including my method for keeping my alignment the same before/after.


And a few shots of the CSL rear bar going in, along with the final installed washer fluid reservoir for good measure. Happy Saturday.

[Bry5on]

Snuck a couple hours in to make the wagon that little bit more M3-like. In prep for the v-brace bracket welding, I installed M3 undertray panels with non-m sedan deflectors in front of the rear tires. I’m happy to report that the M and non-m parts fit perfectly together to support the v-brace while also mating up to the sedan side skirts.


After I got through that, I installed the M3 washer fluid reservoir and ran the wires to the level sensor. I’m waiting for a 5/32” union fitting before I plumb in the hydraulics and switch my wiring to the M3 pump. To fit the reservoir to the bumper carrier, I had to relocate the horn to just under the right side grille as the horn and washer reservoir were occupying the same space.
I may be the only e46 with two washer fluid reservoirs right now.

That’s all for today

[Bry5on]

And now ... we bring it all together. With the suspension modeled in CAD, all the car's measurements, and the known roll stiffness of the suspension setup, we can now calculate travel at the wheels (I'm approximating this within a few percent to keep the math simple) to make sure there's still some travel left and the car won't be on the bump stops. As far as I can tell, the factory setup was about 1/8" off the bump stops at 1G steady state, which seems about what I'd have expected. Maybe my math is off somewhere and cobra can validate my travel calcs . In any case, here's how my setup stacks up with stock M3 suspension (.90" @ 1G):


And with some additional sway bar stiffness (.78" @ 1G):


And to see what happens when we raise or lower the car..

[Bry5on]

Yeah. Bry5on let’s play. There’s only one catch. I’ll only take them if they’re hand painted.

You’re in luck! There’s a town about three miles back that way. I’m sure you’ll find a couple guys there.

Come on by, make a list so we don’t forget anything. I still have your 14mm Allen key and I’ve also got multiple thicknesses of spring pads if you like the Dinan springs and want more suspension travel (or the high roll center

[tlow98]

I regret not doing camber arms last time I had my subframe out. Might be worth to just do them now before you assemble the sedan.

Yeah. Bry5on let’s play. There’s only one catch. I’ll only take them if they’re hand painted.

[heinzboehmer]

Awesome! It’s been a long time since I cheated on my homework in dynamics, so at some point I’ll need to know the critical changes to apply this to my sedan 😂. Who can keep up with that syllabus anyway? Hopefully I’ll just plug and chug with a new weight bias.

The jury is still out until I get my alignment, but I might ping you about those rear LCAs!

I regret not doing camber arms last time I had my subframe out. Might be worth to just do them now before you assemble the sedan.

[tlow98]

Awesome! It’s been a long time since I cheated on my homework in dynamics, so at some point I’ll need to know the critical changes to apply this to my sedan 😂. Who can keep up with that syllabus anyway? Hopefully I’ll just plug and chug with a new weight bias.

The jury is still out until I get my alignment, but I might ping you about those rear LCAs!

[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.