Daytona Beach, Fla. ? Daytona 500 pole-winner Greg Biffle will have to start at the back of the field in today’s race after being forced to change engines.

Biffle’s misfortune bumps up favorite Dale Earnhardt Jr. to start from the inside of the front row when the green flag waves.

Biffle noticed a loss of power during practice Saturday morning. Back in the garage, a valve defect and leaking cylinder were discovered.

“It was a no-brainer. We had to pull the motor out,” crew chief Doug Richert said, standing alongside the No. 16 Ford as the crew made the change.

“We can still win from the back,” he said. “The car is still good.”

Biffle will roll off pit road in the lead position, but will have to drop to the back of the line before the final pace lap.

Earnhardt, who was scheduled to start on the inside of the second row, will move up to take Biffle’s place.

“It’s a two-sided coin,” Richert said. “We’re disappointed he has to start at the back. That opens you up for a melee or some other misfortune.”

But at least Biffle’s team discovered the problem before the rain came, washing out a Busch race.

“If this rain had come earlier, we wouldn’t have been able to practice and we probably would have fallen out of the Daytona 500,” Richert said. “I don’t feel this engine would have made the Daytona 500 the whole race.”

Also forced to drop to the back of the field after changing engines were Ryan Newman, Ricky Craven and Derrike Cope. Scott Riggs, who wrecked his primary car in the qualifying race Thursday, also must go back after switching to a backup.