Note: This kit allows you to upgrade your v2.0 FM frame rails to the full butterfly specification. It is not compatible with the older frame rails. It cannot be mounted to a car without a set of frame rails.
If you don't already have a set of v2.0 frame rails, you're looking for the full butterfly brace.
The butterfly brace "closes the box" for improved chassis rigidity.
First, why do you want chassis rigidity? Because a stiff structure allows the suspension to work better. If your chassis flexes, it's basically a big undamped spring that changes your suspension geometry under load and shudders every time you hit a bump. A stiff chassis will give your suspension a solid platform to work from, leading to better, more predictable handling as well as improved ride quality. There really is no downside. Chassis stiffness is usually measured as torsional rigidity - resistance to twist - because that's how loads usually travel through a car.
When it came time to update the design of our popular and effective butterfly brace, we did it properly. We tested Miatas in a variety of configurations, from a high mileage 1990 to a late NB with the full Sport bracing. Here are some of the highlights:
- our frame rails alone increased rigidity by 17.5% over the late NB (without bracing)
- our butterfly brace took that improvement to 29%
- the butterfly is 11% stiffer than the stiffest NA/NB Mazda ever made - the late NB with Sport bracing
- the new design is stiffer than the original
- the new design is 10% lighter than the original
- the new design has mounting points for a flat undertray (not currently available)
Ground clearance is unchanged from the factory Sport bracing. The new design gives more clearance for various exhaust configurations and is easier to remove if you need to do work like dropping the trans. It's fully compatible with factory front and rear subframe braces. Cars with the "Sport" undercar bracing will have to remove two cross braces in the center. It's made of stainless steel so there is no concern about rust. Naturally, it's made here in the US. The butterfly upgrade adds 13 lbs to the car, low and in the center of the car.
The butterfly brace upgrade adds the center section to an existing set of 2.0 frame rails. If you have our older frame rails then they're unfortunately not directly compatible without welding in some mounting plates.
Lighter. Stiffer. Easier to install. Lower price. Now that is progress.
Miatas with stock headers will likely need to cut the heat shielding off to prevent interference. This is a relatively easy modification.