Honda motorsport chief Yasuhisa Arai believes the Japanese manufacturer's Formula 1 engine output is 25 horsepower clear of Renault, but 40-50hp behind Mercedes.
It's been a difficult return to F1 for Honda, and its tough season continued when its update for the Belgian Grand Prix fell short of ambitious targets set by Arai.
"We haven't caught up to Ferrari yet in terms of the ICE [internal combustion engine]," Arai told AUTOSPORT, adding that he feels the gap is now less than 30hp to Ferrari.
When asked where he believes Honda sits in relation to the other F1 engine suppliers, Arai said: "40-50[hp] behind Mercedes but about 25 ahead of Renault.
"Our engine is a little bit behind Ferrari but much better than the Renault team. Mercedes are still so far away.
"But I have confidence that the second half of the season, we will try hard to catch the top two teams.
"It may be that it will be difficult to catch the top teams as they have good reliability and good combustion characteristics.
"But I want to be close to the top teams by the end of the season."
McLaren went aggressive with the aerodynamic concept on this year's car and that put pressure on Honda to achieve the packaging required for the Woking team's 'size zero' dimensions.
"The package is very tiny, so of course we would like to make it bigger, but compact is better," said Arai.
"This is where we are struggling, because of the size."
When asked if Honda will insist on scope to increase the dimensions next season, Arai said: "No. It will be this package and we will work hard to improve it."