CHARLOTTE, N.C. (AP) — Sam Hornish Jr. is leaving the IndyCar Series for a full-time ride in NASCAR, joining the mass exodus of open-wheel stars fleeing to America's most popular racing series.

The three-time IndyCar champion told The Associated Press he will drive the No. 77 Dodge next season for Penske Racing with Mobil 1 as the sponsor.

''I feel like this is something that is a new and unique challenge for me,'' Hornish said Thursday. ''It may or may not be the right way to look at it, but I feel like I accomplished just about everything in Indy cars. I got to do more than I ever thought I would.''

Penske will officially introduce Hornish as the third driver for his NASCAR team on Saturday night at the Penske Racing Museum in Phoenix. He'll join a team that already fields cars for Kurt Busch and Ryan Newman.

He'll join Juan Pablo Montoya, Dario Franchitti and Jacques Villeneuve as former Indianapolis 500 winners and IndyCar series champions now racing in NASCAR's top series. Patrick Carpentier is also moving to NASCAR after a long open-wheel career, and AJ Allmendinger fled Champ Cars for NASCAR this season.

Scott Speed, who spent the last two years in Formula One, has also migrated to stock cars and will drive in the low-level ARCA Series next year to prepare for NASCAR.

Hornish, last year's Indianapolis 500 winner, has been leaning toward moving to NASCAR for some time. But his struggles in making races — he's failed to qualify for all six Cup races he's entered — had led many to speculate he might stick with IndyCars another year.

But the failure has made him want it more. Although he called choosing NASCAR ''one of the more difficult decisions'' he's ever had to make, Hornish said he has faith he can adapt to stock cars.

''There are so many things that I have elected to do that are a lot easier,'' he said. ''But I've tried to qualify for these Cup races, and it's kind of lit a little bit of fire in me to see if we can't get to the point where I am competitive.