I have to say, even stock mustangs need SFC's. When the guy installed mine with about 60k miles on the car, he said that my frame was already slightly bent from acceleration. Even though he said it was bent in the places that are normal for it to be bent, and that it was nothing to worry about. After welding one end of the SFC's, the other end wouldn't quite reach the frame, and he had to use a hydraulic jack to push the other end up to the frame and weld it. This was the case on both SFC's. He told me that he has done this to many mustangs and this was the case with all of them, unless they were brand new. He said all mustangs need SFC's first thing.