Rob Kinnan
Brand Manager, Mustang Monthly
December 1, 1998
Photos By: Brendan Maze

Step By Step

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Kenny Brown’s Extreme Subs System consists of three parts per side: the subframe connector; the jacking rail, and the Extreme Matrix Brace that ties the other two together.
The first step in installing the subs is making room for them. In the case of this car, GRC had to remove the rivets holding the brake lines in place, so that they could move the lines out of the way.
Since the subframe connectors will be welded to the floor as well as the subframes, GRC cleaned all the crud from these areas to ensure a good weld. This included scraping away the factory caulking, and taking a wire wheel to the sheetmetal.
The subframe connector is initially bolted in place, using the seat belt bolts and a pair of nuts.
Once the bolts are tightened, the connector is welded to the front...
...and rear subframes.
The jacking rail goes on the inside of the rocker panel lip, as shown. The outside of the lip is cleaned up with a wire wheel, then the rail is welded to the lip.
The Extreme Matrix Braces are a cut-to-fit design (due to the factory’s production tolerances). Bert Gizzi holds the brace in position while Phil marks it for length.
The brace is cut with a big cutoff wheel. A hacksaw will work, too, just make sure to get the cut straight.
Once the brace is fitted, everything is welded together.
GRC applied primer and spray paint to all the welds to prevent rusting.
The finished Extreme Subs do a fantastic job of stiffening up this old flexi-flyer.

Subframe connectors are mandatory if you want your Mustang to handle. The world's best suspension system cannot properly do its job if the base chassis is flexing and moving all over the place. For ultimate handling, the chassis must be as rigid as possible. There's a reason why hard-core road racers and drag cars use full-tube frames--they're strong and stiff as hell. In the case of a street Mustang, the quickest, surest way to a stiffer chassis is with weld-in subframe connectors.

A Mustang is what's known as a unibody car. Instead of using one steel frame the length of the car, the Mustang uses a short front frame and a short rear frame. Both, known as subframes, are connected to the floorpan, but not to each other. A subframe connector does just that: it connects the front and rear subframes together, and that effectively creates a full frame, making the chassis stiffer.

Typically, subframe connectors bolt to the underside of the car and are welded to the subframes. That's usually all there is to it. But Kenny Brown has gone the traditional connector one better with the Extreme Subs System. They offer better triangulation to the chassis, which provides even more stiffness and strength over a standard subframe connector.

Kenny Brown's Extreme Subs consist of the standard KB subframe connector, a jacking rail, and an Extreme Matrix Brace to link the connector and jacking rail together. All three provide vastly more rigidity than just a simple subframe connector. All together, the Extreme Sub System sells for just under $300 for '79 to '93 cars, and about $330 for SN-95 cars. We watched as the Gizzi brothers at GRC Performance in Mission Viejo, California, installed a set of KB Extreme Subs on a Fox-body car.