DAYTONA BEACH, Fla. — At first, sports car racing was a lark for Jimmie Johnson, a bit of fun away from his real job.

But expectations change and the two-time defending NASCAR champion now feels the same pressure to win in this weekend's Rolex 24-Hour sports car endurance race as he does when he jumps into his stock car.

"It started off more as something fun to do, and I'm still having a lot of fun," Johnson said Friday before the final practice on the 3.56-mile road course at Daytona International Speedway.

"There's a lot of great things that come with racing a different car in a different series. But, with this team, we're here to win the race and, if not, finish as good as we can to help these guys with the championship."

The reigning Sprint Cup champion, who won the 2006 Daytona 500, will share a Pontiac Riley with former CART champion Jimmy Vasser and defending Grand-Am Rolex Series prototype champions Jon Fogarty and Alex Gurney. The car is one of 24 Daytona Prototypes in the 66-car field.

"It's nice to come down and know that we're going to be a threat and know that what I do on track is important for their season," Johnson said. "There's a lot on the line and the high pressure part of it, needing to perform, is appealing to me."

Johnson, who has driven in America's premier sports car race three times, sandwiching finishes of 36th last year and 28th in 2004 around a second-place run in 2005. He is going to have plenty of big-name competition in the race that begins Saturday afternoon.

Chip Ganassi Racing has two teams hoping to give their boss his unprecedented third straight Rolex 24 title.

Juan Pablo Montoya, last year's top rookie in NASCAR and part of the winning team here in his Ganassi debut, will share the cockpit of a Lexus Riley with fellow defending Daytona champion Scott Pruett, IndyCar champion and current NASCAR rookie Dario Franchitti and Memo Rojas.

The other Ganassi Lexus will be co-driven by former IndyCar champions Scott Dixon and Dan Wheldon, Salvador Duran, also part of last year's winning team, and IRL Pro Series champion Alex Lloyd.

"We know that both of our cars are capable of winning this race, if we can avoid trouble like we did last year," Pruett said. "That's always the key."

The lineup also includes a Pontiac Riley co-driven by Cup champion Kurt Busch, two-time Indianapolis 500 winner Helio Castroneves and the Brazilian's new IndyCar teammate Ryan Briscoe; a Ford Riley shared by Champ Car drivers Graham Rahal and Justin Wilson, along with record-setting, pole-winner Oswaldo Negri Jr. and Mark Patterson, a Ford Riley with NASCAR driver A.J. Allmendinger sharing the cockpit with series regulars Ian James, John Pew and Burt Frisselle; and a Porsche Riley co-driven by Indy 500 winner Buddy Rice, David Donohue, Darren Law and 59-year-old Hurley Haywood, a five-time overall winner at Daytona.