Honda's Yusuke Hasegawa feels the manufacturer did not have enough time to fully prepare the new power unit concept it introduced in the off-season.
Honda has struggled with unreliability and a lack of power this season, but it retains faith in the concept, which it plans to keep for next year.
It currently has several research programmes focused on 2018 running alongside its normal development.
Project leader Hasegawa, who said back in February the move to revamp the power unit was "very high-risk", admits Honda underestimated the challenge of changing concept.
“From the concept point of view, yes, we underestimated it,” he told Motorsport.com. “Although it took a bit of time to stabilise, we understand it was a stage we had to overcome - it was very tough.
“We thought we had enough preparation time, which is why we started this year’s engine development in May, but one year is not enough.
“Theoretically speaking, we have already achieved some good steps. We are in the middle of our target but we need more steps to catch the top runners.”
Honda has found performance improvements for its Formula 1 engine, but it has yet to decide which elements it is confident enough to introduce at the track.
Having made progress on power and reliability when it introduced ‘Spec 3’ of its engine during the Azerbaijan GP weekend, Honda hopes it will be in a position to bring ‘Spec 4’ to one of the early races after the summer break, but will not do so until it is confident in the update.
“We know the target, which other teams have already achieved,” Hasegawa said.
“We know most of the teams are using the same concept of our engine but obviously we don’t know the exact solution, the exact design, the same level of performance we can achieve.
“But we know the direction and we know some elements to achieve that performance, but we still have not concluded what elements we have to introduce.
“[We are focusing] mainly the combustion but also every area, such as fuel consumption, auxiliary parts - everywhere we’re trying to find more horsepower.”