Formula One champions Red Bull are finding potential problems with the sport's 2026 engine because they are ahead of schedule in building their own, according to team boss Christian Horner.
The Briton and double world champion Max Verstappen have both voiced concerns about the characteristics of the new power unit, prompting some speculation that they may be behind on development.
The new unit has a 50-50 ratio of internal combustion engine to electric and Horner has warned that the quickest way around a lap will be for drivers to downshift on the straights to recharge the batteries.
Red Bull, who will be partnered by Ford from 2026 after a complete split from Honda, have recruited engine experts from rivals Mercedes and elsewhere and built a powertrains plant as part of an expanding 50-acre 'campus' in Milton Keynes.
Mercedes team boss Toto Wolff asked in Austria last weekend what Horner's 'real motivation' might be in criticising the 2026 rules and suggested maybe his rival was "frightened" of being uncompetitive.
"I actually think we're in good shape. We've got two-and-a-half years," Horner told select reporters on a factory visit ahead of this weekend's British Grand Prix, referring to "scaremongering".
"I am not sure how close Toto is to his engine business," he added.
"As you start to see the programme really coming to life and as the simulations firm up, [you see] some of the limitations. Which are inevitable.
"So I would say it is perhaps a result of us maybe being well advanced, that we're actually seeing some of the limitations," he added.
Horner felt it was not too late to tweak the specifications, and it would not take much.
"Whether you do it on the fuel flow or the cell mass, you just need to change that ratio slightly to ensure that we get great racing," added Formula One's longest-serving team boss.
Verstappen said in Austria that the data on the simulator "looks pretty terrible".
"If you go flat-out on the straight at Monza... like 400 or 500 (metres) before the end of the straight, you have to downshift flat-out because that's faster. I think that's not the way forward," added the Dutch driver.
"We have to seriously look at this because I mean, 2026 is not that far away. And at the moment, to me, it looks very bad from all the numbers and what I see from the data already."
At Silverstone on Thursday, Verstappen returned to the subject and echoed Horner in saying Red Bull were ahead of schedule.
He suggested other drivers might not yet be aware of a problem.
"I'm just not sure how many are actually fully aware of how it's looking," he said.
Red Bull are also planning a new wind tunnel next to the factory and Horner said the Red Bull engines will carry the prefix DM to ensure the team's late founder Dietrich Mateschitz remains at the heart of the car.