Pierre Gasly and Brendon Hartley will start from the back of the grid following engine changes for the United States GP, it was confirmed on Friday.
Toro Rosso’s engine supplier Honda brought a new C-spec unit to Suzuka two weeks ago and its improvement was notable as both drivers made Q3 for the first time this season.
In the race, however, both would slip back and motorsport chief Toyoharu Tanabe admits development of the engine has continued since the last race to address teething problems.
“On both cars, the new units will feature minor modifications to the specification when compared to that used in the Japanese Grand Prix,” he said on Friday.
“After examining the power units used in Suzuka, we had some concerns and so we have decided to make these changes, which we believe is the best strategy for Toro Rosso for the remaining races.”
Gasly’s completely fresh engine is already installed while Hartley will receive his new unit on Saturday.