NASCAR is making aerodynamic changes, again, hoping to create more competitive racing.

"The rules package is what is on everyone's mind," Brad Keselowski said Friday after a practice session at Michigan International Speedway's two-mile oval.

Part of the intrigue revolves around the fact that no one — including the drivers, engineers and NASCAR officials — is sure how the changes will shake out during the FireKeepers Casino 400 on Sunday, when Joey Logano will be on the pole.

NASCAR is reducing sideforce to cars by setting the rear toe to zero. It is also shortening the spoiler from 3.5 inches to 2.5 inches, reducing the splitter located under the bumper to 2 inches and resizing the deck fin to match the spoiler. After the aero package makes its debut at Michigan, it is expected to be in place again for next month's race at Kentucky.

"The car, as it goes through the air, it casts this aerodynamic shadow," said Gene Stefanyshyn, NASCAR's vice president of innovation and racing development. "And, we're trying to make this shadow as small as possible so the other cars around it don't feel the effects of the shadow."

At least one driver, Aric Almirola, is confident the results will be good for a series that has occasionally great racing but also clunkers.

"At least with the cars behind, they won't be affected as bad with the dirty air we talk about all the time," Almirola said. "I feel like continuing to make the race cars sleeker and get more and more downforce off the car is going to continue to allow more air to flow to the cars following and that will in turn put on a better race. I am really excited about the fact that not only is it really cool to go 220 mph at the end of the straightaway, but then we have to slow down to 180 mph in the corner."

With all the changes, the start of qualifying was delayed by 15 minutes Friday. Keselowski's car was among the final ones cleared to enter the track as teams tried to do everything they could within the rules to give their drivers an advantage.

"They are trying to get everything they can get," NASCAR senior vice president for competition Scott Miller said. "It's even more critical with the skew rules as we have them for them to try and push the envelope."

The sanctioning body has reduced the downforce on cars from 3,000 pounds in 2014 to 1,500 pounds with the latest aero package. It also removed 110 pounds of sideforce from cars this year. The tweaks are aimed at putting the handling of the cars back in the hands of the drivers.

Keselowski said the changes led to speeds being "blazing fast," on straightaways and much slower on turns.

"You enter the corner almost 220 mph and you turn left and the front goes and the back doesn't always go with it," Keselowski said. "That is quite a feeling for sure. It is a unique challenge that I think will bring out some of the best racing we have seen in quite some time. I am really optimistic about it and hoping that we can turn this opportunity into a victory here at Michigan."

Keselowski, who is from suburban Detroit, has won twice this year and 19 times in his career. Keselowski's best performance in 14 Sprint Cup races in his home state was a second-place finish in 2012.

"For me, it puts a lot of pressure coming to this race," he said. "I have had to be really careful to try to take a step back because I get really mad when we don't win this race and we haven't won it yet. Maybe that means the day I win it, if we win it, I will be ecstatic. It is really a key race for me personally and for the sport. I am glad we get to come here twice a year."