Foxbody Chassis

The Foxbody chassis is of a unibody design. This means that rather than having a full frame running the length of the car, the Foxbody uses a set of subframes at the front and rear of the car, connected by the floor pans. Pretty much every modern, mass-produced consumer car uses this design (generally, only trucks use a real body-on-frame design) without issue. The problem with this design in, terms of its use for the Foxbody platform , is that Ford did not include enough bracing for even the stock engine's 225HP output. After years of abuse, it is actually pretty easy for these engines to twist and distort the stock chassis, especially for convertables! Properly bracing the chassis is a must for the Foxbody Mustang (really, any Mustang).

Use the links below to answer common questions regarding subframe connectors and overall stiffening of the chassis.

Subframe connectors
Bolt-on subframe connectors
Weld-in subframe connectors
Bolt-on vs weld-in
Which SFC should I choose?
SFC quality: eBay vs name brands
Couldn't I make my own subframe connectors?

Torque Boxes
Torque boxes

Subframe Connectors

The purpose of a subframe connector is to essentially connect the front subframe with the rear subframe. Starting at the front subframe, they run the under the floor pans, and link up to the rear floor pans.

Bolt-on subframe connectors

Well, as the name implies, a bolt-on subframe connector is installed by bolting them in. The idea behind them is to target the do-it-yourself enthusiast that does not have access to or the ability to weld. They usually include seat supports (which is good). To install them, essentially you drill two holes (at each end, for each connector) perpendicular to the factory subframes, overlap the aftermarket connectors, slot the bolt through and tighten them up. From an installation standpoint, it is certainly not complicated. They will stiffen the car up noticeably, but I feel that over time the shear forces being placed on the bolts will eventually elongate the holes, allowing for play in the connectors.

Weld-in subframe connectors

Weld-in connectors are not much different from the bolt-on;s, apart from that they are welded to the factory subframes. Overall, weld-in's will provide greater rigidity. If you're wanting to pick up a set, look for ones that have seat supports too. The seat support is an extra bracket mounted on a connector that bolts to the seat mounting point in the floor pan and provides some extra strength.

Weld-in vs bolt-on subframe connectors

Which to choose? I quite often see this question across different forums. Usually, bolt-on SFC's are cheaper, but in my opinion, the best option is to go with a nice set of weld-in subframe connectors. You might have to spend an extra $50 getting a shop to weld them in for you, but they definitely provide better bracing and overall rigidity to the chassis. Furthermore, a weld-in can act as a jacking point without worry of breaking anything. I am not too sure how the bolt-on variety would fair, as again all the stress would be placed on the bolts and the holes they are sleeved in. I personally would not use a bolt-in as a jacking point. That being said, bolt-on connectors are definitely better than no connectors, but to choose between the two, I would go with weld-in 100% of the time.

Which type to choose?

If you haven't got the gist of yet, weld-on subframe connectors are the preferred choice. Quite simply, a weld provides a much stronger bond and a more durable connection than a bolt and is therefore much more suited to the task of bracing the unibody.

Now, every brand from A to Z seems to have their own subframe connectors on the market. Sifting through them all to make a decision can actually become quite a chore. As previously concluded, full-length, weld-in subframe connectors are the recommended piece of choice. Which company to choose? There are so many to choose from... Kenny Brown, Maximum Motorsport, Steeda, UPR, Team Z, J&R... the list goes on. Furthermore, some come unfinished, some come tubular, there are many options.

SFC quality: eBay vs name brands

During your search for subframe connectors, you may notice that the prices can range anywhere from $70 a set to as much as $230 a set. Of course, everyone wants to get the best deal possible and save money where money can be saved. Now, this begs the question, what is the difference between say a cheap no name brand versus a more expensive name brand? To answer this, kpgubert, a member here on the site, has some personal experience to share. (source)

  1. Cheapies Verses Quality Subframe Connectors: To make a long story short, when I first realized I really should have SFCs in my car I bought a pair off ebay. They are short, thin-walled twigs. I never even bothered installing them, I can tell you they would be next to pointless. I have seen reputable places (like LRS) sell pieces that look similar. I would just make a clear note to people that they should not skimp on the quality (price) of these. Even the best ones money can buy (MM and possibly UPR, imho) still aren't that expensive. Another alternative would be to ask someone who has used a certain piece first.
  2. Bends Verses No Bends: It seems to be that quality SFCs have pre-bends in them to conform to the location of the front and rear subframes (no, they don't lie in the same vertical plane). Cheap ones like what I linked to are just straight pieces of steel (SVE). I think the intention is you just bend them to fit the car. And actually, they are pretty easily bent. If I set one of the ones I have up on a stair and stand on them, they bend a lot. If my skinny ass can significantly deflect it, I wonder what my 3500 lb. car would do...
Couldn't I make my own?

When you get right down to it, subframe connectors really aren't a complicated piece at all. Rather, they are just tubular steel items pre-cut to a specified length to fit on Foxbody Mustangs. Could you fashion your own homemade subframe connectors from material available from the local hardware store? If you are very handy and confident in your abilities to work with metal (bending, welding, cutting), yes, I certainly think you could fabricate your own for the fraction of the cost of an aftermarket set. What you do want to watch for is the quality and thickness of the tubing. It is easy enough to walk into the local hardware store and pickup some generic steel tubing, but that generic tubing may or may not be up to the task. There usually isn't much detail about the tubing at hardware stores, so be careful. An alternative would be to give a metal or machine shop a call and see what they can source for you.

So yes, it is more than possible to make your own subframe connectors. However, I would caution you that unless you are pretty experienced with metal and have a good source for materials, to otherwise hold off. The aftermarket has taken all of the guess work out of the equation and their connectors are proven to fit and stiffen things up. If anyone reading this has fabricated their own set, feel free to chime in via the forums.

Torque Boxes

The torque boxes are the metal plate like looking pieces at the back of the car where the lower control arm connects to. Just like the subframes, the torque boxes are a prime location on the Foxbody frame for reinforcement. Out of the factory, the torque boxes are simply spot welded in place. Hard launches, even from just a stock setup, can thrash the torque boxes beyond recognition. A simple stamped steel plate is enough to reinforce the stock boxes if they are still in good shape. If they are cracked or otherwise heavily damaged, you have a pretty big project on your hands. The whole rear pretty much has to come out as well as the interior to reinforce or repair the torque boxes. It is not as easy as an oil change, but not out of reach of the committed do-it-yourselfer. Again, welding experience or a welding connection is a must.

The aftermarket sells pre-cut plates that are ready to weld in. Or, just like the subframe connectors, if you are comfortable working with metal, you can always fabricate your own. Mind you, if I recall correctly, the aftermarket reinforcements cost around $25 a set, which isn't too heavy.

A Stiffer Ride

At the end of the day, subframe connectors are the minimum that should be done. They won't add power, but they certainly will improve how the Foxbody rides and handles! Subframe connectors are considered to be the #1 priority modification, and for good reason. The stock unibody design just isn't up to the task of dealing with the 5.0L engine up front. The torque boxes too ought to be given some serious consideration too, particularly for hardcore racers.

Additionally, I would like to add a section to the above article regarding through-the-floor subframe connectors. If anyone reading this has any experience with through-the-floor subframe connectors, it would be a great help if you could chime in via the official chassis FAQ forum thread or by emailing me directly through the contact page.