By 2000, Audi would still compete in the US with their RS4 for the SCCA Speed World GT Challenge, through dealer/team Champion Racing competing against Corvettes, Vipers, and smaller BMWs (where it is one of the few series to permit 4WD cars). In 2003, Champion Racing entered an RS6. Once again, the quattro four-wheel drive was superior, and Champion Audi won the championship. They returned in 2004 to defend their title, but a newcomer, Cadillac with the new Omega Chassis CTS-V, gave them a run for their money. After four victories in a row, the Audis were sanctioned with several negative changes that deeply affected the car's performance. Namely, added ballast weights, and Champion Audi deciding to go with different tyres, and reducing the boost pressure of the turbocharger.