NASCAR inspectors discovered the two Toyota teams, which competed in Saturday's race with Tony Stewart and Joey Logano driving, had placed magnets on the cars' accelerator pedals. The magnets, at least in theory, would prevent the pedals from being fully depressed, which would limit the engines output and distort the horsepower data.
NASCAR confiscated the two engines and was able to perform accurate dynamometer tests, said Robin Pemberton, NASCAR's vice president of competition. Pemberton said any penalties would be announced this week.
"Their ass needs to be kicked out of there. They're shiftless," Chevrolet team owner Richard Childress said of those responsible at JGR. "They (NASCAR) just need to do something."
"I'll say it's damn blatant," he said. "I'm surprised they got caught. When people get an advantage, they don't want to give it up and sometimes they go to extremes to keep from giving up an advantage, and that's just what they did."
Ford owner Jack Roush, who has often been critical of Toyota's NASCAR efforts - particularly of the Japanese automaker's move to the Sprint Cup Series last season - was equally disgusted.
Roush actually spent more time faulting NASCAR for creating the problem by allowing Toyota to operate with newer engines in the series - which promped NASCAR to reduce the Toyota's horsepower last month.
"It's a loop that's unaffordable," Roush said. "I can't afford to do a new engine for Nationwide right now. NASCAR can establish parity with the tests that they've done or they can leave it be.
"If they leave it alone, they will establish not only the Truck series, but also the Nationwide series as a single manufacturer's bastion."
For his part, JGR president J.D. Gibbs admitted Sunday that members of his Nationwide programs did, indeed, attempt to alter the outcome of the dyno testing - an action he called a "poor, foolish decision."
"I want to apologize to NASCAR, our partners, the Toyota guys. A couple guys made a decision there that impacted all of us. To me the big question is why?" Gibbs said.
"I know they were frustrated and wanted to make it look like we're handicapped (on horsepower) even more than we were. I understand that, but that is not an excuse."
Gibbs said he had a good idea who was involved and that the organization would address the issue internally, regardless of penalties NASCAR levies against the teams this week.
In a statement released later at the track, team owner Joe Gibbs said his organization would accept "full responsibility and any penalties NASCAR levies against us.
"It goes against everything we stand for as an organization."
Last month, NASCAR announced rule changes for the Toyota engines used in the Nationwide Series. The new guidelines were intended to cut about 15 horsepower. Saturday's race at Michigan was the first since that change in which horsepower was expected to play a larger role in performance.
So far this season, JGR's No. 18 and No. 20 Toyotas have combined for 14 wins in 25 races, with the most recent being Kyle Busch's victory at O'Reilly Raceway Park in Clermont, Ind., in late July.