NASCAR's horsepower cut hurting Tony Stewart's Sprint Cup form

Stewart has not won a race since the June 2013 Dover event, and a sixth place at Bristol is his only top-10 finish so far this year, leaving him 28th in the championship.

His last two seasons have also been interrupted by two sprint car incidents, the first leaving Stewart with severe leg injuries and the second involving the death of competitor Kevin Ward Jr.

NASCAR reduced horsepower from 850bhp to 725bhp for 2015 as part of a package of changes that also included a small rear spoiler.

Stewart said difficulty adapting to the change in car style was the biggest issue hampering him this year.

"We're desperately trying to figure out what it's going to take to move the needle," he said.

"It's a scenario that when you drive for so long, you're used to one thing.

"Coming into this year and taking the amount of horsepower they took out was a pretty radical change for the Cup Series.

"I think it was more the horsepower reduction than it was anything, that I feel like has hurt me this year.

"I've grown up driving high-horsepower cars, high power-to-weight ratio cars. This hasn't been what I'm used to feeling."

The Stewart-Haas co-owner - whose team has won four races with reigning champion Kevin Harvick and Kurt Busch this year - dismissed any suggestion that his crew chief Chad Johnston was part of the problem.

"I still really like working with Chad Johnston," said Stewart.

"I don't feel like he's what's holding us back.

"There's something about the way this package is that just doesn't suit my driving style.

"I'm holding him and the team back versus vice versa."

He believes it would only take one breakthrough performance to turn his form around, but admitted the continued struggle was demoralising at times.

"Every weekend, I feel like it's the weekend we're going to find it," he said.

"It's disheartening, takes the wind out of your sails when you realise you haven't found it that week.

"If we get our car working and win a race because we have our car working well, it definitely can turn the season around. With this format, it can change everything.

"That's your reason not to give up. That's your reason to keep fighting every week and show up at the track with the same attitude you did the week before."