Roush explains engine failures

Matt Kenseth's unit failed as early as lap six and on lap 72 his teammate David Ragan faced a similar fate. Then on the penultimate lap of the race, Carl Edwards' engine expired while he was closing on a top-five finish.

Roush reckons his team probably misjudged the engine speed they would be running during the race as they didn't expect the new tyre specification selected by Goodyear would allow them to run as fast as they eventually did.

"I think we misjudged how fast this tyre was going to be and the engine turned more," said Roush. "It's the same spec on the engine that we had all of last year. It wasn't something new or experimental, I had great confidence in it.

"We had it the last third of last year, but we saw more RPM with it in qualifying than we ever had and we saw more RPM in the race than we ever had. The tire didn't fall off as much as we expected it to, so the tire did a real nice job but we just over-revved the engine."

Roush also believes they chose the wrong axle ratios for their cars, bringing engine speed up and putting the components under increased stress. Initial inspections pointed at a broken valve causing Kenseth's failure, while a broken valve spring might have caused Ragan's one.

"We had a choice of which rear axle ratio to use and we used the higher of the ratios and it was 200 RPM more than the other ratio would have been," Roush added. "We just made the wrong choice from a crew chief and from an engineer point of view on that.

"If we can go back looking at it I'd say I need to have more margin in the engine and it needs to be not that close to its limit, but if you go through and win the races we won last year late in the year in the chase and we had the success that we had in Fontana, there's no reason to be nervous about it.

"The fact that it crept up a little bit didn't raise the alarm that it should have. We'll be wiser going to Atlanta."

Roush also admitted that following the first two failures, Carl Edwards, Jamie McMurray and Greg Biffle were told to look after their engines.

"They told them that they needed to try to hold the RPM down if they could, so for that they didn't turn it as hard as it wanted to go in the corner, so you give up the end of the straightaway, which is unfortunate," said Roush.

"But you run as close to the limit as you do and as hard as the guys try, you have to squeeze every ounce out of every component in the car."

Engine-related issues affected at least nine drivers during the weekend at Las Vegas. While five Toyota drivers had to change engines before qualifying, none of them faced issues during the race and Mark Martin retired with an engine failure for the second week in a row.

Roush Fenway's Kenseth led the series' standing heading into Las Vegas, but he dropped to third in the points following his early retirement last Sunday.