 Foster also drove in the USAC Championship Car series, racing in the 1964-1966 seasons, with 28 career starts, including the 1965 and 1966 Indianapolis 500 races.He finished in the top ten 10 times, with his best finish in 2nd position in 1966 at Atlanta.Foster and Mario Andretti became best of friends, building a close relationship which Andretti claimed he would never do again with a fellow racer because Foster's death so significantly affected him.