McLaren would have won races in 2016 if it had the best Formula 1 engine, according to its racing director Eric Boullier.
The Woking-based team has not won since the 2012 Brazilian Grand Prix, a run of 78 races - the longest in its history.
Its Honda power unit was off the pace in the manufacturer's first year back in F1 in 2015, but the Japanese firm made strides during its second season.
"If we had the best engine this year, we would have won races," Boullier told Autosport.
"We know, the GPS traces [of corner speeds] tell us."
Boullier says improvements need to be made in tandem on the engine and chassis in order for McLaren to keep moving up the grid.
"There is room for improvement everywhere with Honda," he said.
"It also drives your chassis development. Everything is connected.
"You can't make a car too draggy if you don't have enough power deployment because you lose time.
"You have to balance all the time. We work as one team with Honda to achieve what we want."
Boullier believes Honda has made progress and reduced the deficit to its rivals but conceded it will take time to catch up completely.
"The gap has closed," he said. "But to get where Mercedes is, you can't just copy and paste.
"There is a way you have to go through.
"You can't do it in three months or six months but in a few years.
"It took Renault time [to make engine gains] and still today, they are not on top of the game.
"They started to develop this engine six years ago."