Moss Miata
Flyin' Miata Butterfly Brace

FM Butterfly brace

[2/16/2013] Reviewed by: Evan Bedford

Applicable to: '90 - '97 1.6 liter

Just an update on my previous review.

After an Alberta winter full of daily driving over very bumpy side streets at extremely cold temps, I found that it performed admirably. My main reason to install was to stiffen things up so that I could bolt down the hard-top (I had heard horror stories about bolted down hard-tops cracking either the rear window or the fiberglass in the cold).

And I found the bolts that I thought had dropped out of the box. When hunting down some bubble wrap for a non-related shipment, I found them taped to the wrap.

Over 30 minutes to remove completely

FM butterfly brace

[7/5/2012] Reviewed by: Evan Bedford -

Applicable to: '90 - '97 1.6 liter

A brace which connects the two frame rails, in order to add stiffness to the chassis.

The brace arrived in two boxes (one with the wings and one with the „thorax‰). The wings box only had foam in one end, so the pointy end of the wings pushed through the cardboard during shipping. There may have been some bolts included in the kit to attach the thorax to the wings, but I suspect they slipped out of the hole. I had installed the frame rail reinforcements a couple of years ago, so at least I didn‚t have to go through that again. But the gas and hydraulic lines were no less of a hassle (perhaps even more, since the wings now took up that much more space). I finally got the wings bolted in (driver side easy; passenger side a headache). Then I hoisted the thorax into placeand found that there wasn‚t enough room for it! So I unbolted the driver side wing and with a small, round file, I extended the bolt holes by about 1/8‰ (you can only go so far before you hit the vertical edge of the wing). And I shaved off a chunk on each of the washers so that they would snug up to the vertical edges. And then I crossed my fingers. But it didn‚t do any good. Still not enough space. So I had to remove the passenger side wing (with all of the hassle associated with the gas and hydraulic lines) and extended the bolt holes on it about 1/8‰ (and shaved down the washers). So including getting the car on jacks and removing the seats and carpet and putting everything back together, I spent 7 hours.

If anyone is following down this path, I would highly recommend bolting the wings and thorax together on the garage floor initially and then do some measurements first. Bolt holes to corresponding bolt holes on the wings. Then measure from bolt to corresponding bolt on the two frame rails. And it wouldn‚t hurt to use a straight-edge (I used a laser level) to ensure that the bolt holes are perfectly aligned (I found that some of the holes in one wing were out by about 1/8‰ to 3/16‰). Then, if something is a bit out, you can find out before you‚ve wasted an hour or two grunting and swearing underneath the car. Once the brace was on the car, it seemed to do the job it was intended to. Without the chassis flex absorbing some of the bumps, I could now feel more of the imperfections in the pavement. I have the hard-top bolted on, so I haven‚t yet had a chance to see if the cowl shake has disappeared, but I don‚t doubt what others have said about the brace‚s effectiveness on this matter.

Over 30 minutes to remove completely

Flyin' Miata Butterfly

[1/31/2007] Reviewed by: Daniel Born -

Applicable to: '90 - '97 1.6 liter 1.8 liter

This is the "butterfly" brace that includes the frame rail reinforcement kit and butterfly brace.

Pros: really stiffens up the car. This is especially true on older Miatas as they have less braces to begin with and probably have a little more "looseness" due to age and mileage. Cons: On my 92, there is not enough clearance between the exhaust system (downpipe just ahead of the cat) and the brace. Even after pounding the heck out of the OEM downpipe's "lip" and cutting out a bit of non-essential metal on the brace, there is still only about 1/4" of clearance between the two. When the exhaust is hot and the engine is under load (made even worse if turning right), the exhaust will come in contact with the brace and cause some very uncomfortable grinding and vibration noises in the car. I don't like what you have to do to your brake and fuel lines to make this central "butterfly" section fit. You have to strain them and pull them down from the car's underside, leaving them in greater danger of damage, especially on a car this low. I keep scraping on objects (rocks, bad pavement, cement ramps, speed bumps, etc.) with the "butterfly" part even though my car isn't lowered at all. Installation and removal of the central butterfly parts is a real pain (but that's just a minor annoyance in the end). Conclusion: It does wonders to the car's handling but due to several problems with the central "butterfly" part of the brace, it's coming off. I will keep the frame rail reinforcements though as they don't cause any problems at all (besides, I've got 16 holes in my floorboard that need something to put in there). I expect to loose some stiffness but am ready to live with that.

The product is great and does work as advertised but for me, the central butterfly section is not worth the hassle.

Difficult to remove without leaving damage

Flyin Miata Butterfly Brace

[3/25/2006] Reviewed by: Dave G

Applicable to: '99 +

Butterfly brace and frame rails

Installation: There are 3 steps with this install.

1. Remove interior carpeting.

2. Line up rail and drill up through the body. When doing this, at least on the NB, make sure the front of the rail is right on the seam as the directions state. Others have posted that you should move the rail back slightly. If you move the rails back 1/8th of an inch you’ll have a problem drilling the last hole; the drill bit will not come up into the interior of the car. FM has spread the holes out as much as possible, so if you don't follow directions, you'll be in trouble.

3. Install all of the bolts. The center section is brutal as everyone else has posted. FM is currently working on ways to make this part of the installation easier. In the current setup, you'll need an open ended wrench and socket set with a universal joint. Buy some socket extensions and joints (not the glaucoma relieving kind, although after contorting your hands and tools in new and creative ways, the pain relief may be welcome). This step goes MUCH quicker if you have another kind person to hold the wrench on the nut while you tighten the bolt on the other side.

4. A month later, go and retighten everything. I expect everything to settle after a month of being under load. As a result, some bolts may not fit as tightly as they initially did.

Performance: Improvements:

1. Let me first point out that I installed the rails and brace at the same time. As a result, I can't differentiate the improvement from the individual parts. My instinct is that the rails help more than the brace.

2. Everything feels solid. You know how your OTM is fine over some sections of road, yet your Miata shakes and rattles on those sections? Well, your Miata just became your OTM in that respect. That "My car is having a seizure" feeling is gone. You'll still feel big bumps when your shock runs out of travel, but that is the case with any car. I highly recommend this mod for a daily driver.

3. The performance of the car feels like it is improved, but the only way to really determine this objectively is to time oneself before and after on a well known stretch of windy road. Unfortunately, I haven't done this. Skip Cannon claims that his autocross times were lower with the brace installed


1. You will lose ground clearance. Expect to lose 1/4 of an inch to 1/2 an inch. My car, equipped with S-Tech springs (which lower the car about 1-1.25 inches) went from just enough ground clearance, to just short of enough clearance on speed bumps. Since this car is my daily driver, I will have to install taller springs as my next mod.

2. I think that it could be argued that the car is slightly less communicative with the brace. If you want as much feedback from the road as possible, you will feel less of it with a stiffer frame, and should pass on the BB. You won't lose all or even most of the feedback, but you'll lose some of it. Again, if you want to feel every bit of the road, don't get this mod. If you want a car that isolates you from most road imperfections, buy another car. If you want a car that is still communicative, but isn't going to jolt and shimmy on imperfect roads, this is your mod. I love it.

Difficult to remove without leaving damage

Back to Product Reviews 15 January, 2014

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