Red Bull's push for the championship has been aided by the engine Honda introduced in France, however Toyoharu Tanabe has denied claims the power unit has as much as 15 brake horsepower more than it did before.
Max Verstappen and Sergio Perez have won the last four races and are the favourites to add to that streak this weekend at the Austrian Grand Prix. Mercedes have been vocal about Red Bull's improved straight line speed in recent weeks, however the Honda technical director made it clear no performance updates are allowed during the F1 season.
"I'm very happy if it is true, but it's not true," Tanabe told RacingNews365.com and other members of the media. "Under current regulations, any performance update is not allowed to be applied during the season.
"As a result, our second PU is the same as past PU in terms of specification and performance."
When asked if the performance of the current engine has been improved by advancements in reliability, Tanabe stated it came down to the hard work done by Honda, Red Bull and AlphaTauri.
"The current performance improvement is a result of the hard work from Honda and the teams," Tanabe added. "Under the current PU regulation we need to submit any changes, so [we are] only allowed to change for durability or cost reasons.
"We need to submit very detailed [reports] to the FIA first and they approve the changes. The FIA distributes all the documents to the other PU manufacturers. So we need to have approval from the other PU manufacturers to change any single parts and specifications.
"So we are very careful to [make] change to the performance and it is not possible to improve the performance during the season."