Richard Westbrook admits Corvette is struggling to understand its pace deficit to the rest of this year's Le Mans 24 Hours GT field.
The American marque has been a GT frontrunner in recent editions of the endurance classic, triumphing in 2011 and spending several spells at the front of last year's event before being hit by technical woes.
Neither of the C6-ZR1s got within four seconds of class pole in 2013 qualifying however, a gap Westbrook admits has taken the squad by surprise.
The #74 Corvette's qualifying best of 3m58.644s was almost three seconds slower than its 2012 best.
"We don't come here to make up the numbers, so we're not happy about the situation," Westbrook told AUTOSPORT.
"We were able to do 3m55s in qualifying last year and essentially we're here with some small improvements and we're struggling for pace, so something has clearly gone wrong.
"The car is always well suited to this track, aero-wise we're very good, but this year, for whatever reason, it hasn't happened.
"I don't think it's any secret that we're very slow down the straight. We're trying to get to the bottom of it, but it definitely wasn't in the plan and it definitely wasn't expected.
"We don't sandbag; we're an honest team. We're holding our hands up and saying we've got something wrong here, which we're trying to put right."
Despite the deficit, Westbrook is optimistic the team can find solutions that will allow both Corvettes to be a factor in the 81st running of Le Mans.
"We have between now and 1530 tomorrow to get on top of it. We have the right guys to do it," he added.
"For one thing a small problem can hurt massively, because it's such a long track.
"For the last two years we've also been the quickest car and leading by a comfortable distance, and not won [the #73 car prevailed in 2011], so you can never rule anything out at Le Mans.
"We'd never hope for others' misfortune because that's a bad attitude, but we've just got to focus on a faultless race and see where that takes us."