Kyle Busch has had to apologise for a foul-mouthed tirade aimed at his team's engine suppliers Toyota Racing Development, which followed a frustrating end to last weekend's Cup race outing at Dover.

The #18 car of Busch and the #11 of his Joe Gibbs Racing team mate Denny Hamlin failed to get sufficient fuel mileage in last weekend's AAA 400, forcing both drivers to pit from the lead ten laps from the end of the race which was eventually won by Brad Keselowski, whose Dodge engine was able to last the distance.

Furious by the late-race reversal of fortune which saw him lose out on the win after over 300 laps in the lead, Busch let loose over the team radio: "Thank you, TRD. [Expletive] us out of another one. Piece of shit, mother[expletive]."

Although there was no immediate reaction to the comments on Sunday, TRD president Lee White finally broke his silence on Wednesday and made it clear the company was not happy with Busch's outburst or conduct.

"We're extremely disappointed in his negative comments and the tone of the comments after the event," White told the Charlotte Observer. "It is under discussion as we move forward. We certainly are very disappointed."

Busch clearly realised that he had gone too far and issued a public statement of apology for his comments on Thursday.

"I made some remarks out of frustration on my radio at the end of last weekend's race in Dover that were very misguided," he said. "I owe my friends at Toyota and TRD an apology. We have a great partnership with TRD and they built me a motor that helped me lead over 300 laps and nearly lap the field.

"It's just frustrating that the caution fell where it did and suddenly it became a fuel mileage race and we were set up for maximum horsepower," he added. "Obviously, that worked well for most of the day and you can't control when the cautions will fall."

It's been a disappointing 2012 Sprint Cup season for Busch, who failed to make the Chase for the championship by just 3pts behind Jeff Gordon, after a season that has seen a number of engine issues for the #18.

White responded with a more conciliatory tone, saying that he understood Busch's passion for racing and for winning.

"At TRD and Toyota, we have that same zeal for racing - and winning," he said. "Kyle's had a frustrating year with several car and engine mechanical failures which were not his responsibility, and we're working extremely hard on our end to improve our products and processes."

He added: "We will continue to address these issues, but we're ready to put this behind us and move forward with the remainder of the season, including the Toyota drivers battling for the championship."

Although Busch failed to make the Chase, his team mate Denny Hamlin is in third place in the title battle behind Keselowski and Jimmie Johnson. Also still in Cup championship contention are Michael Waltrip Racing team mates Clint Bowyer and Martin Truex Jr., who also use engines from TRD.

Busch's car owner Joe Gibbs tried to strike the appropriate balance between the two sides of the spat.

"It has been a frustrating season for Kyle in many ways when you think about some of the issues we've had with that #18 team this year and obviously some of those frustrations carried over to his finish last week in Dover," he said. "However, Kyle recognizes that his comments and the tone of his comments were misguided.

"We've been able to work through this issue and I think everyone is ready to get back to the focus being on racing and Talladega," he continued. "We have a great relationship with Toyota and obviously they are a major part of everything we do at Joe Gibbs Racing."