Toyota and Chevrolet teams seemed to dominate last week-end’s Bud Shootout at the Daytona International Speedway, and one of each is on the front row for Sunday’s Daytona 500.

But a number of the premier Chevrolet and Toyota drivers will be starting at the back of the field in today’s Dual 150 qualifying races.

They’ve had to change engines after premature wear was discovered in the valve lifters was discovered.

(more after the jump)

Oddly, the same problem has hit both Toyota and Chevrolet. In comments from a Toyota team official, the part involved appears to be a special racing part likely made by the same company and used by both Toyota and Chevrolet.

All four Hendrick team drivers – Jimmy Johnson, Casey Mears, Dale Earnhardt, Jr., and Jeff Gordon – changed engines and will start at the back of today’s races. So, too, did Scott Riggs, whose car uses a Hendrick-sourced engine.

Toyota is changing engines in the cars of Tony Stewart, J.J. Yeley, Dale Jarrett, and A. J. Allmendinger.

The move does not affect the starting row for the 500 itself, because that was set in qualifying last Sunday. Jimmy Johnson has the pole and Michael Waltrip will start on the outside of the front row. But the engine changes may affect the starting position for the other cars because the unique procedure employed for the Daytona 500 bases the remainder of the starting positions on where a driver finishes in the two 150 mile “Gatorade Duel” qualifying races held today. Finishing position in the Duels can also determine whether some drivers can get into the 500.

For that reason, the Duel presents tight, fast racing – in which an accident in the middle of the field can collect a number of cars running further toward the back. Then, too, faster cars in the back will have to work their way through the field to get to the front, further adding to their exposure.

But it also seems certain to provide exciting racing, as some of the best drivers and cars will have to pass almost the entire field to win.

The Gatorade Duel is on Speed, starting at 2 p.m. ET today (Thursday).

The Daytona 500 is Sunday at 2 p.m., ET, on Fox.