Adamowicz returned to sports cars, racing TransAm in an Autodynamics Dodge Challenger as teammate to Sam Posey, achieving second place in the 1971 24 Hours of Daytona in a Ferrari 512S, shared with Ronnie Bucknum, and third place in the 1971 24 Hours of Le Mans with Sam Posey in a 512M After the decline of the Can Am and F5000 formulas, he moved to IMSA series and won the 1979 GTU championship in an Electramotive Nissan 280ZX and 1982 GTO championship in an Electramotive 280ZX-T.