Clint Bowyer was fastest in opening Cup Series practice at Atlanta with a lap of 180.152 mph.
The Stewart-Haas Racing driver ran just six laps in his No. 14 Ford. Bowyer was followed on the speed chart by SHR teammate Aric Almirola, who clocked in at 179.988 mph.
Completing the top five were Austin Dillon (179.772 mph), Kurt Busch (179.405 mph), and Denny Hamlin (178.931 mph).
The 1 hour, 20-minute session saw a mixture of teams focusing on race trim as well as qualifying trim. As the lone practice session of the day, teams will qualify for the Folds of Honor QuikTrip 500 Friday evening.
Filling out the top 10 in practice were Martin Truex Jr. (178.884 mph), Erik Jones (178.798 mph), Kyle Busch (178.781 mph), Joey Logano (178.729 mph), and Daniel Suarez (178.729 mph).
Atlanta is the first weekend where part of the new rules package will roll out.
Noticeable on the cars is the eight-inch spoiler and larger splitter. Horsepower has been reduced from 750 to 550. Teams are not using the aero ducts on the front of the cars this weekend as Atlanta is one of the few tracks where heavy braking occurs.