The S197 (2005 and up) Mustangs have a significantly more rigid frame than previous year Mustangs, so we do not recommend any chassis stiffening for street, autocross and open track cars. However, if you are building a race car, frame stiffening is a valid option since you can never have a chassis that is too stiff in a race vehicle. In such applications, we still advise concentrating on removing excess weight first since the vehicle is heavy in stock form.
Except for racing, please do not be tempted to purchase chassis stiffeners offered for sale by some unscrupulous merchants and manufacturers. The only result of installing subframe connectors or frame stiffeners on an S197 Mustang or Shelby will be a heavier car and a lighter wallet!
For more information please read the following:
"GR40 Kit for 2005+"