Due to the growing market demand for Cobra Replicas, many of which fell short of the standard set by the original 427, Shelby began production of the CSX4000 series in 1997. These cars are based on the 1965 Shelby Cobra 427, but with modern features such as a stronger frame, higher quality alloys in components, and improved cooling and heat shielding. These cars offer various build options such as an aluminum or fiberglass body choices. Buyers could also specify their choice of suspension components, such as springs, shock absorbers and braking systems, giving these continuation series cars a greater variety of final specifications. Production continues today, with more recently produced cars falling under the CSX6000 VIN categorization, due to lack of availability of CSX4000 VINs.