He first raced in the IRL in 2000 with the PDM team, with a best finish of third. However, he swiched to Panther for the next season and improved enough to take the title from reigning champion Buddy Lazier. In 2002 the Penske team switched from ChampCar, and Sam was able to beat their driver Helio Castroneves to his second title.

For 2003 msot of the established top US open-wheel teams were now racing in the series, with Honda and Toyota providing engines superior to the established Chevrolet unit Panther used. As a result, Cosworth was called in to supply a replacement enigne informally dubbed the Chevsworth, with which Sam was a winner again, finishing 5th in the 2003 standings. For 2004 he moved to Penske, winning the season-opener but finding that Honda, and not Penske's Toyota's, were now the engine to have. 2005 has been an improvement, as he currently lies third to Dan Wheldon in the standings. Longer-term he is rumoured to be keen on a switch to NASCAR with Penske and Toyota.

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