Chad Knaus, crew chief for three-time defending NASCAR Sprint Cup champion Jimmie Johnson, has a reputation for pushing the envelope when it comes to creative ways of finding speed for his racecars.

In effect, NASCAR on Wednesday sent a message to Knaus and fellow Hendrick Motorsports crew chief Alan Gustafson, who prepares the No. 5 cars for series points leader Mark Martin, to stop pushing, when it comes to certain areas of NASCAR's racecar.

After Johnson and Martin finished first and second, respectively, Sunday at Dover International Speedway, and after both passed post-race inspection at the track, NASCAR took their cars to its research-and-development center in Concord, N.C., for further examination.

"The 48 and 5 were brought back to the R and D center," NASCAR said in a statement released Thursday afternoon in response to media inquiries about the status of the two cars. "We've been doing this since the inception of the new car as a part of routine post-race inspection. We bring the winner and a random pick back to the R and D center after each event. While both cars passed post-race inspection, we informed the 48 and 5 they were extremely close on some of the tolerances."

The sanctioning body indicated Friday to Sporting News that the primary area of concern was the body at the rear of the car, which was approaching the limit of allowed deviation from the center line. In other words, the car was pushing the envelope in terms of the degree the body was "yawed-out" or offset.

NASCAR's implied admonition was clear -- don't risk penalties to the top two drivers in the Chase for the Sprint Cup by pushing the limits too far.

According to Sprint Cup Series director John Darby, the Hendrick cars exceeded the nominal values published in the rulebook and came close to overshooting the tolerance, or margin of error, NASCAR allows its competitors.

"The numbers that we publish in the rulebook in most cases are the nominal or 'Here's-what-you-must-be' numbers,'" Darby said. "The claw grid (templates) that we use, the height sticks -- most of our checking devices -- have that nominal number indicated, as well as colors. Take our height stick, for example. There's where the number's supposed to be, then a green area, a yellow area and a red area. The green is your working area that's published in the rulebook. Yellow is what we're going to give you in good faith. When you hit red, you've gone too far. If you want to relate it to that type of a situation, Hendrick's cars were at the line that defines the difference between yellow and red.

"There's no further to go. That means you're putting 100-percent confidence in NASCAR's officiating to duplicate that exact measurement week after week after week. On most occasions, we probably would be able to do that, but on the one week we go to the red side of that line, the risk and reward is just not worth playing it that close."