Black & Tan 332iT

[Bry5on]

I was pondering torsional rigidity last night - do you think there would be anything at all to be gained by replacing the 2x transmission/exhaust tunnel brackets with a single torsion plate across those 8x mounting points? Not from the perspective of preventing the tunnel from spreading out /collapsing in but in terms of helping to prevent longitudinal twisting? In theory it would make a non-zero difference, but the two brackets are fairly close together so not sure if there would be much, if anything, to be gained in practice? The non-M3 convertible had a similar sort of thing (although I believe that was only 4x mounting bolts not 8). BMW didn't do that on the M3 vert though so 🤷♂️

I was just talking with some friends about this. I think the cabrio part is the answer as in that case the four inner fasteners won’t be doing much. I’m keeping my eye out for one and will swap if I come across one. It’s also lighter which doesn’t hurt.

[karter16]

On top of that, it does seem to be even more torsionally rigid when exiting extreme driveway angles.

I was pondering torsional rigidity last night - do you think there would be anything at all to be gained by replacing the 2x transmission/exhaust tunnel brackets with a single torsion plate across those 8x mounting points? Not from the perspective of preventing the tunnel from spreading out /collapsing in but in terms of helping to prevent longitudinal twisting? In theory it would make a non-zero difference, but the two brackets are fairly close together so not sure if there would be much, if anything, to be gained in practice? The non-M3 convertible had a similar sort of thing (although I believe that was only 4x mounting bolts not 8). BMW didn't do that on the M3 vert though so 🤷♂️

[Bry5on]

As you know, I “just” got the M3 and have no cracks and yet to schedule my reinforcement. Your brace, even if I got the exact fit, doesn't fit the coupe, right? Just trying to understand where to throw my wallet.

I'm doing my front suspension refresh next weekend - been dealing with family stuff. I'll grab your address and ship it all to you

Sweet, thank you!

This v-subframe-brace fits the M3 only. Since my wagon is converted to all M3 underneath, it fits my wagon The top X-brace behind my fold down seats will not fit the coupe as it's substantially different back there though.

I'll get this cart saved for sharing so you, Heinz, Stas, and any of the other Bay Area folks can do a batch order to save on pricing.

[YoitsTmac]

If I had an M3 with no cracks in the floor I'd do this, solid subframe bushings and a rear-only vincebar install and call it done. That would be a huge upgrade in performance and stiffness with almost no downside (the slight NVH of solid subframe bushings). Then add a Slon wall if you're alright losing the fold down seats and making that compromise.

As you know, I “just” got the M3 and have no cracks and yet to schedule my reinforcement. Your brace, even if I got the exact fit, doesn't fit the coupe, right? Just trying to understand where to throw my wallet.

I'm doing my front suspension refresh next weekend - been dealing with family stuff. I'll grab your address and ship it all to you

[Bry5on]

Great stuff! loving following all this and seeing all these rigidity improvements.

(also amused by the growing number of intake scoops on your bench in every new photo)

You know, I've got to throw an easter egg in there for you!

Got the chance to put more miles on the setup today, and all of the above still holds except for #3 - after warming up the gear oil, the m-clunk is still there, although it's now a more muted m-thud without the distinct clunk noise there. Additionally, I've got a lot more shifts in and it's very noticeable there. The drivetrain doesn't really wind-up or wind-down so there's less active thinking and feathering of the throttle to make shifting smooth. Tip-in and tip-out are way more responsive but also way smoother. That slight delay on throttle lift before you can feel the deceleration seems to be very nearly gone, and starting from a stop is easier to be both smooth and quick at the same time, whereas before it was kind of one or the other. My wife and I also both thought the car was quieter on the highway.. bonus. I was skeptical that I might have just been experiencing the placebo effect after the change, but I'm no longer skeptical.

Also now that I've had more time with it, I'm super convinced that this will mitigate subframe carrier failure. Feeling the absence of the movement has convinced me just how much carrier movement there was and even still is with the vincebar alone. If I had an M3 with no cracks in the floor I'd do this, solid subframe bushings and a rear-only vincebar install and call it done. That would be a huge upgrade in performance and stiffness with almost no downside (the slight NVH of solid subframe bushings). Then add a Slon wall if you're alright losing the fold down seats and making that compromise.

[karter16]

Early days and not a whole lot of seat time but I can say reasonably confidently that the hypothesis has been validated, and this brace mitigates a lot of that flexibility.

Great stuff! loving following all this and seeing all these rigidity improvements.

(also amused by the growing number of intake scoops on your bench in every new photo)

[Bry5on]

Another win today.

This evening I decided to install the first version of the v-subframe-brace.

As a recap, the hypothesis is that:
1) The remaining rear bump oscillations I felt after installing the X-brace are related to a lack of fore-aft/bending stiffness
2) The subframe can rock forward aft, sort of 'around' the axle axis, under throttle application, related to subframe mount failure, and the stock v-brace is not enough to constrain this movement
3, unstated so far) The m-clunk is related to 2) and additionally, the subframe floor acts as a bit of a speaker, amplifying the clunk






I wasn't thinking for a bit and ended up installing M6 rivet nuts instead of M8 rivet nuts, probably because I decided to do this on jack stands instead of driving the 2 miles down the street and getting on the lift. At some point I may try to remove the M6 guys and go to M8 as the design intended, but we'll see how we get along for now.

Early days and not a whole lot of seat time but I can say reasonably confidently that the hypothesis has been validated, and this brace mitigates a lot of that flexibility.

Response and oscillations following bumps are much tighter, and throttle applications are more 'instant' and don't have that coil-up feeling that the e46 has. You can be a bit rougher with throttle application and removal and it doesn't feel as rough on the chassis, it just follows your foot.

I've only got a handful of miles on the car, attempting to provoke it of course, but so far I haven't been able to get it to m-clunk. You can for sure get it to cluck by going on/off/on/off throttle very quickly, but this is true even on the newer G80 cars. Shifting feels a little smoother? Not so much in the lever, but in the car itself. Definitely need more miles to validate this.

On top of that, it does seem to be even more torsionally rigid when exiting extreme driveway angles. I can tell again that the front is less rigid than the rear. I wonder if recreating the e30 cabrio front strut mount gusseting would be useful. I'm really going to have to do those control arms and a new set of bushings now.

Anyway, pleased with this! The car has really transformed a generation or two in ride feel in the past few weeks.

[Jamesone]

Awesome build..

[Bry5on]

V-brace to subframe brackets showed up today, press fit nuts and powder coat both look great. If I'm lucky I'll get to installation this weekend.



I also ordered stainless pistons for the 996 calipers to hopefully finally get rid of my pad dragging issues. Removing the additional Porsche pad dampers seems to have helped a bit (also with pedal feel) but I've still managed to get that loud brake hum and I'm seeing pad wear differences between inner/outer pads on my freshly rebuilt calipers. Good times.

[Bry5on]

Today another package arrived - powder coat looks great. Also featured here is a hell of a garage hack - a used stainless 8' x 3' kitchen prep table as a nice hard wearing workbench! Pretty stoked with this.


I made a mistake and ordered the spacers as 1/4" instead of 3/8" so I'll need to order more of those before I bond everything into place. Otherwise the M8 holes and slots all fit up really well, so I think the flat patterns are all set. To get the clevises oriented right, you've got to hold the brace up to the edge of the clevis while you torque it down like so:


It's not all sunshine and roses though, the bolt and clamp strategy is not as nice to assemble as the stud and nut version as you've got to disassemble more things and it gets pretty fiddly. I've got another part coming in from sendcutsend that's got powder coat and press fit inserts, so I may try doing press-fit nuts and going back to studs if that works okay. Anyone got any recommendations for press-fit nuts?

Going in:

Seats down:

Seats up:

Cover in place:

I'm pretty sure there's no difference in stiffness, or at least not much, from removing the top bar although I'm driving myself nuts second guessing and trying to feel something.

[karter16]

Very exciting - can't wait for this!


Sent from my iPhone using Tapatalk

[heinzboehmer]

I think these are the possibilities:

1. Karb snorkel is not the same dimensionally as OE.
2. My intake isn't fully seated.
3. My car's bumper fitment is off.
4. My car's stamped aluminum brake duct bracket is far too bent out of shape (I know it is at least somewhat messed up).
5. Scanned car has some tweaked dimensions thanks to the fender bender.
6. Some unknown differences between early and late model years.

Okay so it turns out that none of these were correct. Actual culprit was the wishbone bracket under the airbox. Guess it got bent at some point:



Duct fits great with the bracket bent back to where it should be!

[Bry5on]

Might not actually be the worst idea to have a gap and flexible section, to accommodate the engine twisting under load.

Excuse to print something in TPU :P

By design there’s a 25mm gap and a flexible ‘accordion’ TPU boot. The boot slips over the duct, then the CSL snorkel ‘clips’ into the boot like factory and pulls the boot up slightly. The boot has 20mm of engagement so it can act like a slip joint and also can deform axially/radially. It’s the yellow modeled part in the section view above

In fact it would be better if you could attach something to the snorkel shaped like a funnel that goes over the intake pipe to decrease the chance of air turbulence and ensure the air gets rammed in regardless of engine tilt.

There is also a lead-in to the TPU boot to transition the ID smoothly instead of into an abrupt lip. I think this makes 0 difference practically but makes my OCD much happier. Also can be seen in the section view above.

[heinzboehmer]

Might not actually be the worst idea to have a gap and flexible section, to accommodate the engine twisting under load.

Excuse to print something in TPU :P

Bryson already designed that in

Issue with my car is that the duct alignment is too far off for the TPU coupler to accommodate (hence why I left it off for the pictures).

[YoitsTmac]

In fact it would be better if you could attach something to the snorkel shaped like a funnel that goes over the intake pipe to decrease the chance of air turbulence and ensure the air gets rammed in regardless of engine tilt.