After a series of tests, Clarke was signed to drive in the
Champ Car World Series for
CTE Racing-HVM, in 2006 as a teammate to
Nelson Philippe. The team owned jointly by
Cedric the Entertainer and
Keith Wiggins. Clarke finished sixth at
Portland International Raceway and seventh at
Burke Lakefront Airport, where he was battling for second with
Mario Domínguez when they collided on the penultimate lap. Clarke also competed at
San Jose, moving up from ninth to second before a gearbox failure put him out at mid-distance. In his next race, in Denver, Clarke moved into third-place on the final lap because of a collision of two drivers ahead of him to achieve his first podium finish as a Champ Car driver. The Denver third-place was the first podium finish for a Champ Car Rookie driver in the 2006 racing season. Following on from Denver, Clarke continued to run at the front and narrowly missed out on another podium finish at the next race in Montreal, coming home in fourth-place. Immediately after, Clarke won the Bridgestone Pole Position award at Road America, Wisconsin. He was the first rookie to do so since 2003 and the first British Rookie since Nigel Mansell in 1993. Clarke experienced misfortune towards the end of the season, which saw him forced to settle for "Rookie runner-up" to
Will Power after an intense battle between the two drivers. Clarke returned to the team for the
2007 season, now named Minardi Team USA, joined by new teammate and former Minardi and Red Bull Racing F1 driver
Robert Doornbos. Clarke had a troubled season, finishing 13th in the overall standings and missing one race. He missed the race at
Zolder, having been ejected from the event for causing a multi-car crash in practice. He did, however, record a second-place at Road America. Upon the folding of the Champ Car series into the
IndyCar Series, the Minardi team became known as HVM Racing and hired
E. J. Viso to drive, leaving Clarke without a team. ==2009==