Eric Boullier says McLaren ideally need to know in September which engine they will be racing in next year’s championship.
Although Honda are keen to continue with McLaren in 2018, at least publicly, there have been rumours of late suggesting that the Japanese manufacturer will withdraw from F1.
There are, however, also rumours that they could team up with Toro Rosso, which would pave the way for McLaren to swap to Renault power.
But whatever happens, Boullier says ideally McLaren need a decision in September.
Asked how late they could leave it to make the final call, the Racing Director told Autosport: "Technically you could change an engine in 12 weeks.
"You can change it anytime before the season up to three months before.
"If you want to do a base design around an engine, it's September."
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