Dreaming: Miata-style butterfly brace

[xLibelle]

I have a close friend that works heavily with miatas and we have discussed this component and the possibility of something like it for the e30 but investigating the potential design needed.... lets say it would be difficult to produce the outcome thats gained with the miata.
We've heard a bunch of good feedback from the FM belly brace and the design of that car benefits greatly from it. The e30 on the other hand is a totally different design than the miata though.
Here's the reason for its need in the Miata. The car is based around subframe design and the Power Plant Frame (PPF). The body just ties the frames together at key points with bushings. (there's 22 of them in total btw, thats a lot of rubber.) Remove those few bolts and you can pull the body off and end up with this:

The butterfly is key to triangulating the rigidity of the entire car. Something the e30 could possibly use, but doesnt have the problem that the miata does.

A couple points on the e30 are worth mentioning though - front end and rear end... obviously. The control arm bushings can be solidified from moving toward or away from each other... explained here. (And in Red below)
The rear subframe motion can be dealt with by installing solid SF bushings. But also the addition of something like what the Miata rear subframe has that ties it to the body of the car is feasible. The two bars can be seen in the miata belly picture in rcko's post.
The rest of the bodies structural rigidity is addressed with heat shielding and other brace work below the drive shaft, above the exhaust. But here could be a suggestion for realistic bracing, though i dont know if it would be worth it. (In green)
The quick sketch is not a proper design, but rough idea at what points describe possible linear deflection... or whatever.

[Coco Savage]

interesting.

[Wishno87]

good insightful post

[92 mtechnic cabrio]

What kind of ground clearance would the e30-version butterfly brace have?

two of my miata friends have lowered miatas and have had their butterfly braces ripped off (along with damage to the cars' original parts from having the brace ripped off the car)

can't blame FM for that though, or anyone but themselves, they have the same beliefs in ride height as I do

[kishg]

looks interesting. i think this would benefit verts more than coupes/sedans.

[mxseven]

Ok, first time I've looked at this thread since I posted, so I'll try to answer a few questions.

1. FM butterfly brace is made from 12 and 14GA stainless steel. Tin snips WILL NOT apply here. I wouldn't call it heavy gauge, but it's plenty sturdy. There are hidden gussets welded in at key locations that make it work like heavier material, while being relatively light (35lbs I think, all in).

2. Large exhausts, trannies, and typical ground clearance figures are both very helpful in knowing the feasibility of this product. How much room is available to design around is critical.

3. The Miata subframes are NOT tied to the unibody with rubber. They are solidly bolted. The control arms, however, are attached to the subframes using rubber bushings, 18 of them. The drivetrain is isolated from the chassis with rubber, and the PPF attaches the diff to the tranny without either one of them being bolted directly to the unibody. this was done to minimize drivetrain slack, reduce NVH, and ease the factory assembly process. All that said, the Miata chassis has a fundamental issue that makes it inherently more flexible than most other cars. It's a convertible. A lot of what the butterfly does, IMO, is take care of that problem. That's not to say it wouldn't help the E30, and that's why I originally asked how flexible the E30 is out of the box, compared to similar cars.

Thanks for everyone's input so far, I'll try to keep track of this thread more...

[devonjordan]

Ok, first time I've looked at this thread since I posted, so I'll try to answer a few questions.

1. FM butterfly brace is made from 12 and 14GA stainless steel. Tin snips WILL NOT apply here. I wouldn't call it heavy gauge, but it's plenty sturdy. There are hidden gussets welded in at key locations that make it work like heavier material, while being relatively light (35lbs I think, all in).

2. Large exhausts, trannies, and typical ground clearance figures are both very helpful in knowing the feasibility of this product. How much room is available to design around is critical.

3. The Miata subframes are NOT tied to the unibody with rubber. They are solidly bolted. The control arms, however, are attached to the subframes using rubber bushings, 18 of them. The drivetrain is isolated from the chassis with rubber, and the PPF attaches the diff to the tranny without either one of them being bolted directly to the unibody. this was done to minimize drivetrain slack, reduce NVH, and ease the factory assembly process. All that said, the Miata chassis has a fundamental issue that makes it inherently more flexible than most other cars. It's a convertible. A lot of what the butterfly does, IMO, is take care of that problem. That's not to say it wouldn't help the E30, and that's why I originally asked how flexible the E30 is out of the box, compared to similar cars.

Thanks for everyone's input so far, I'll try to keep track of this thread more...

Exactly why I want one, e30 Vert

[mxseven]

Hey, I just want to bump this thread again to see if anyone in the Lexington, KY area has a car they'd like to offer to put on jackstands and get a good look at, and possibly be a guinea pig for this project. Also, are there any E30/BMW events held in this area annually?

[rcko]

posting in general discussion might help... add the link to this discussion.

Maybe an admin can shime in and help get in contact with a member from KY.

[m42technic]

Having owned both E30's and a Miata, I'm not convinced that non-vert E30's have a whole lot to gain from a butterfly brace. Miata's (especially early models) feel worlds better with additional chassis bracing, but sedan E30's arent exactly noodles. I'm sure it certainly wouldn't hurt, but I'm not certain the gained rigidity would be very substantial.

[mxseven]

Thanks. Do the verts and non verts look the same underneath?

[scabzzzz]

Having owned both E30's and a Miata, I'm not convinced that non-vert E30's have a whole lot to gain from a butterfly brace. Miata's (especially early models) feel worlds better with additional chassis bracing, but sedan E30's arent exactly noodles. I'm sure it certainly wouldn't hurt, but I'm not certain the gained rigidity would be very substantial.

I believe this as well. Would a proper cage not fix all this chassis flex? If we're talking about HPDE or higher, cage would be assumed to begin with for safety and rigidity. At that point, the solid state CAB's should do enough of the work. Right?

I was driving down my 6 story garage after really cold weather the other day, and I could hear my car flex because it was so cold out by driving dwon the ramps. Weird stuff. I could hear exactly where the weak points were at and they all seemed to be mid section of the car drivers side and passenger side.

[soul rebel]

It would a great product for e30 verts, I'd like on on mine.

[jw 325ic]

id buy one for sure...

but why not make something like this:
http://www.turnermotorsport.com/html...RODUCT_ID=E36X

the e36 "X" brace

[m42technic]

id buy one for sure...

but why not make something like this:
http://www.turnermotorsport.com/html...RODUCT_ID=E36X

the e36 "X" brace

Because you can already use E36 x-braces on your E30?