Vehicles that use a unibody structure lack the stiffness required for drag racing applications. You can put a full roll cage in a car to address this, or you can also add a set of subframe connectors to create a more rigid structure. The two types of subframe connectors; under car and through the floor, are discussed in this video by Dave Zimmerman from Team Z Motorsports.
Subframe connectors are designed to tie a unibody car together and prevent the chassis from excessive amounts of twisting and flex when it launches at the drag strip. When you prevent the chassis from twisting and flexing, it allows for more horsepower to find its way to the ground and make sure the vehicle has plenty of traction. If you’re serious about racing a late model muscle car like a Mustang, a set of subframe connectors should literally be one of the first upgrades you make to the car.
Subframe connectors that go under the car are designed to be welded in at a rear contact point and a front contact point. These types of subframe connectors come in a variety of styles, are designed to provide plenty of ground clearance, and stiffen the entire chassis. If you want something a bit more extreme, a set of subframe connectors that go through the floor of the car might be what you need. As the name implies, these subframe connectors will run through the floor on the inside of the car, and will provide locations to tie a roll cage too.
Dave does a great job explaining the pros and cons of both types of subframe connectors in this video. You also get to learn what shape of materials provides makes the strongest type of subframe connectors. To learn more about each type of subframe connector you can visit the Team Z Motorsports website right here.