Nissan North America's decision to leave the Indy Racing League's was not unexpected. Rumors of such a move have circulated through the IRL garage for more than a month.

For more than a year, Infinitis have shown increased muscle.

Cheever Indy Racing accounts for both of Infiniti's IRL wins. Tomas Scheckter's Texas pole last weekend was the Japanese auto maker's second pole, with Eddie Cheever taking the top starting in Fontana, Calif., in March. Scheckter also led the most laps in this year's Indianapolis 500 and looked on his way to giving Infiniti its first 500-mile victory.

"I am only sorry that we came just shy of delivering an Indy 500 win to Infiniti, which would have made them the first Japanese automotive manufacturer to win the race," Cheever said.

Infiniti will remain with the IRL as engine supplier for the League's new development series, the Infiniti Pro Series, which debuts later this year at Kansas Motor Speedway.

According to John Schilling, spokesperson for Nissan North America, the Pro Series will be a better fit for the auto giant.

"The Pro Series allows us to supply stock Q45 engines to TWR who will make racing modifications and sell the engines to race teams competing in the series," he said. "Supplying production Q45 engines for use in this series aligns well with our marketing goals."

When Infiniti started with the IRL in 1997, its race engine was based upon the Q45 production engine, but designed specifically for Indy racing. Subsequent editions of the engine strayed farther from its production model roots, until it became regarded as a high horsepower rival to the IRL's other current supplier, Chevrolet.

In addition to Cheever's team, Nissan powers cars driven by Shigeaki Hattori, Laurent Redon and Robbie Buhl. All have led races this season.

"The Nissan's are powerful," said Boomtown 500 winner Jeff Ward.

"We have turned their Indy Racing program into a winning effort," said Cheever, owner of Nissan's lead development team. "Along the way we have successfully enhanced their image as a performance-focused luxury car maker."

Still, Chevrolet -- and before them, GM cousin Oldsmobile -- had dominated the series. They have been the dominant engine since the IRL switched to a normally aspirated formula in 1997.

"We have the best engine out there on the track right now," Cheever said. "We have until September to kick everybody's butt."