Scramble mode: Teams trying to get handle on new rules package

Greg Biffle (left) talks with Roush Fenway Racing general manager Robby Reiser at Las Vegas Motor Speedway.

Todd Warshaw/NASCAR via Getty Images

With just two races in the books for the 2014 NASCAR Sprint Cup Series season, top drivers and teams are already wondering what kind of impact new aerodynamic tweaks and a rules change will have on performance.

Las Vegas Motor Speedway, site of Sunday’s Kobalt Tools 400, is the first of 11 Sprint Cup races on 1.5-mile tracks this year and the first race where the new changes really come into play. Daytona International Speedway has its own rules package, different than what’s used at intermediate tracks, and Phoenix International Raceway is a one-mile track where speeds are about 50 miles per hour slower per lap than at Las Vegas.

And every time NASCAR changes its requirements, some teams are fast immediately, some flounder and some do both.

Take Greg Biffle, who was 34th fastest during Thursday’s four-hour marathon Las Vegas practice that saw his Roush Fenway Racing teammates Carl Edwards and Ricky Stenhouse Jr. finish 27th and 29th, respectively.

"Last year I was the fastest on Thursday, probably the third-fastest on Friday, 12th on Saturday and I was 25th on Sunday," said Biffle after Thursday’s test. "This year I’m 34th on Thursday, and hoping that I’m about 20th tomorrow and maybe 12th Saturday and win on Sunday, but that’s about as good of an analogy I can give you on what is wrong and why our fastest car is 27th. I really honestly wish I had more to tell you about it, but we just aren’t getting a hold of the racetrack is about the best I can say."

Photos: Thursday and Friday scenes from Sin City -- It's NASCAR in Vegas

Biffle actually did better than he expected in Friday’s lone 90-minute practice round, finishing 10th, while Edwards was fastest in the session, ahead of Joey Logano, six-time NASCAR Sprint Cup Series champion Jimmie Johnson, Stenhouse and Jamie McMurray.

Johnson, a four-time Las Vegas winner, said he’s unsure about the performance of his No. 48 Hendrick Motorsports Chevrolet.

"I think how we run here will dictate our testing schedule," Johnson said prior to practice on Friday. "If we don’t have the speed or feel like directionally we are going down the right road, it would be useful to test on a bigger track soon."

Matt Kenseth, second in points to Johnson last year, agreed that it’s still too early to figure out exactly where his Joe Gibbs Racing team is at relative to the competition.

"Nobody’s raced here, obviously, with this new no-ride-height rule and with the new aero package and the bigger spoiler and all that stuff," said Kenseth. "It’s a little bit of an unknown, really, until you get going. I think today get qualified and then really get through a race practice tomorrow before you have a real good idea. I haven’t got the chance to catch up with Denny (Hamlin) or Kyle (Busch) after the test yesterday.  But, I was encouraged with what we saw yesterday. So we’ll just have to see how the weekend goes."

There’s no question, though, that the racers will be paying close attention to how things go this weekend.

"Everybody knows the mile-and-a-halves make up most of our season, so you’ve got to run well here, and so far, so good," said Clint Bowyer.

Kyle Busch said he expects passing to be more difficult on Sunday.

"Air is at such a premium — we’re running through the corners faster than ever," said Busch. "The faster you go, the more air you want. I don’t know if that’s going to make it any easier to pass guys just going through the corner faster."