Leading Honda IndyCar driver Graham Rahal has accused Chevrolet's teams of sandbagging in recent tests at Indianapolis.
Superspeedways were Honda's strong point last year, but Rahal said recent tests at the home of the Indy 500 where James Hinchcliffe's Schmidt-Peterson Dallara-Honda set the pace at 227mph and the best Chevrolet speed was 223mph was "a complete joke".
"You have to be cautious about judging our engine rivals," he said.
"To believe they were 4 or 5mph off... Come on guys, we know better than that. No way. I'm not an idiot.
"Sandbagging is one thing but if you're going to do it, at least be close to what you're really capable of."
Two private tests took place at Indy late last month, with Penske running alongside the Honda teams at one and then the Chevrolet teams running together at the next.
Penske driver Will Power's engineer Dave Faustino insisted Chevrolet's problems were real.
"The windy conditions made it hard to judge, but I'd say when we ran the test with the Honda cars, we felt they were very fast and when we ran with the Chevrolets, it felt like we were all close to each other," he told Autosport.
"It's not like one Chevy team had found something that we as a team had been lacking."
He admitted Chevrolet had not shown its maximum performance level in the tests but was adamant it needed to improve to match Honda in the Indy 500.
"We're not running the engines too hard, but we're definitely hoping for more, come May," Faustino said.
"We felt like we were at a bit of a deficit last year, and it seems like Honda has improved since then.
"So we're a bit worried, and hoping Chevy can respond.
"We've got to hope that the step they make is big enough."