McLaren-Honda braced for engine limit 'challenge' in 2015

Engine use restrictions have been further tightened for 2015, with the previous allowance of five power units now reduced by one.

Honda has struggled for reliability during pre-season testing, managing only 1087 miles of on-track running through the winter sessions with works partner McLaren, compared to Mercedes' benchmark 11,413 across its four teams.

When asked by AUTOSPORT whether the new limit of four engines per driver was of particular concern to McLaren-Honda, given its problems so far, Boullier said: "Yes, it is in some ways.

"We are preparing ourself and Honda to run just four power units per season, but we saw some last year struggling with five or six, so four will be a big challenge.

"But I think it's not only [a challenge] for us."

Boullier admitted that as Honda's problems had been the main limiting factor in McLaren's build-up, it could not judge the reliability of other areas yet.

"It is true that we have some reliability issues around some ancilliaries around the engine and because we have not done the mileage, we cannot say we have discovered all the issues we can face on the chassis," he said.

"You have a running order unfortunately and until the power unit is working we cannot develop the car as well."

Jenson Button said that while Honda's reliability had been challenging, the company's approach and the engine's driveability gave cause for longer-term optimism.

"I think the two things I am most impressed by Honda with is their determination. Even when things are really tough which it has been for all of us as McLaren-Honda for the last few tests, they will work flat out to get the engine ready for the first race, which is great," he said.

"And you know they will improve during the year, give it their all and never give up.

"The other thing is the driveability, that's really impressed me.

"It's something you are always worried about as it is the unknown, but we have made massive steps.

"That is the area I am most happy about with the engine.

"On both sides, everyone is working very closely together, Honda helping McLaren and McLaren helping Honda in certain areas, so it's good to see."