There are different kinds and types of sub-frame connectors. For our purposes, we'll mostly talk generally about what they do and how they do it. Sub-Frame Connectorsbasically are made to tie the front and rear sub-frames together. Unibody cars don't have a traditional frame like early cars. When you apply lots of rear wheel torque, you get body twisting and stress applied. Sub-Frame connectors help prevent chassis flex which usually fatigues, and eventually cracks, metal.
Sub-Frame Connectors Stiffen the Car - With a stiffer chassis that resists body torque, you get power transferred to the ground to propel you forward quicker. We've all seen the view looking at the front of a car leaving the line at the drag strip. The car lifts one wheel off the ground higher than the other. That is engine torque being transferred to the ground and the chassis and body reacting to the torque. All of that body torque takes time. The body is moving in a different direction, rather than straight down the track. It's not much time, but in drag racing, small amounts of time are everything. A stiffer chassis will allow a quicker launch and should lower your ET. Over-flexing a chassis will stress it and cause the chassis metal to crack. Sub-Frame Connectors are good insurance to help you keep your car together longer.
Sub-Frame Connectors Improve Handling - A stiffer chassis will handle better by keeping more of the load in the suspension components. Rolling through a corner will cause all 4 tires to be loaded differently the more the chassis and body flex. Sub-Frame Connectorscan make a car feel more stable in the corners as well.
Many Sub-Frame Connectors provide seat mounting braces. These braces keep the floor pan from flexing under the seat area. This translates to less movement of the driver because the driver's seat is more rigid and will not sway back and forth. Without sub-frame connectors: Picture the car flexing and the seat (driver) moving as well. Add both movements together and you get quite a lot of driver movement. Adding sub-frame connectors can lessen the overall driver movement.
What to look for in a set of full length Sub-Frame Connectors:
Sub-frame connectors usually work better when they are welded in place. Some manufacturers offer the choice of weld-in or bolt-in. They know not everyone can weld or has a welder. Bolting them in is a good option if you can't weld them in. Depending on the kind you buy, they may or may not affect ground clearance. Many of the better products are powder coated for longevity and convenience. Compare different products from different manufacturers to see what size steel they are being made of. Heavy steel is better to a point. Lesser gauge connectors should probably be avoided. Go with a quality company. Remember, sub-frame connectors are generally a permanent addition to a car. They will be responsible for handling a lot of torque. Choose the better quality sub-frame connectors.