He moved to CART Champ Car racing in 1996 as a replacement for Jeff Krosnoff, who was killed in the previous race in Toronto. In 1999, he joined the more competitive Rahal team, almost winning the US 500 before running out of fuel, and finishing fifth in the series. He started the next year by winning the 2000 season-opener, but failed to finish in the championship Top 10. In 2001, he won twice and finished sixth overall, but was dropped by the team, mainly due to two collisions with teammate Kenny Bräck. In 2002, he competed with Sigma Autosport, scoring two third places finishes at Long Beach and Milwaukee, before the team folded due to financial problems. The Italian did a partial season with PK Racing in 2003, with a best result of fourth at Road America. Papis also raced in the 2002 and 2006 Indianapolis 500s for Cheever Racing, claiming a 14th-place finish in his second appearance. He mostly concentrated on sportscars since 2001, remarking that "Champ Car needs me more than I need it" as the series struggled to fill its grid for 2003 after many teams defected to the IRL.