After several weeks of escalating media build-up, NASCAR was finally back in action at Daytona International Speedway on Friday afternoon at the start of Speedweeks 2012 following the winter off-season.

Matt Kenseth recorded the fastest time of the day with a lap of 44.607s (201.762mph) on the 2.5-mile tri-oval, with Jeff Burton just 0.005s off his time by the end of the first practice session of the year.

Measures to reduce or eliminated the controversial two-car tandem draft racing that dominated at the circuit last season seemed to be largely successful, with large-scale two- and three-wide pack racing re-emerging as the preferred way for cars to circulate.

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Unfortunately that meant that when there was an accident at the front of a pack - as happened when Tony Stewart got into the back of Kurt Busch and turned the #51 Phoenix Racing car near the end of the first practice session at Daytona - a number of cars were involved in the fall-out.

As well as Stewart and Kurt Busch, Penske Racing teammates Brad Keselowski and AJ Allmendinger had to start getting the back-up car out of mothballs for Saturday night's Budweiser Shootout, as did Joe Gibbs Racing's Kyle Busch.

Jeff Gordon was also involved and sustained light damage from contact with Keselowski, but opted to sit out the rest of the day so that the team could repair the primary car rather than fuss over the back-up.

"I just barely got into the #2 car," said Gordon. "Very minor damage."

Stewart took the blame for the wreck: "I was pushing the #51 car and he had to move a little bit, but I'm still the one pushing him so I'm responsible for it," he said.

"It was just a deal where Tony was trying to help," agreed Kurt Busch. "We were just trying to learn the draft and a couple of slow cars were emerging in front of us. I slid up to go around them and I thought it was smooth but I got turned around. So now we'll just bring out the back-up."

Allmendinger confirmed that it looked like the racing style at Daytona was returning to the old ways. "It's back to pack racing," he said. "To a certain extent you could already see cars in the pack already overheating; everybody's anxious."

The second scheduled practice session in the evening for the 25 Budweiser Shootout entrants was shortened because of rain and only 12 cars set times.

Earlier in the day there had been drama in scrutineering, when Jimmie Johnson's #48 car failed its technical inspection and was found to have modified bodywork that exceeded NASCAR tolerances.

Officials removed the part of the car known as 'C-posts', part of the bodywork that runs from the rear of the roof and which helps direct the air flow over the rear spoiler, meaning that the modified parts could have given Johnson's car an aerodynamic edge over his rivals. None of the other Hendrick Motorsports cars (of Dale Earnhardt Jr., Jeff Gordon and Kasey Kahne) had any similar issues and all three cleared inspection without incident.

The modification was found on Johnson's Daytona 500 car and does not affect this weekend's Budweiser Shootout event. Because the modification was found and removed in pre-qualifying inspection, Johnson will be able to compete in the Daytona 500 as normal but may face post-race penalties.

Experts pointed to a similar "illegal modification" incident on the #48 at Sonoma in 2007 as being a guide for the sanctions might be levied: Johnson was docked 100pts under the old scoring system, and his crew chief Chad Knaus suspended for six races.

"It's a hell of a way to start the 2012 season," admitted Ken Howes, Hendrick Motorsports' vice president of competition.

Full Friday practice times available.