Toro Rosso has decided to revert to Honda's previous-spec power unit for the remainder of the Russian Grand Prix weekend at the team's perfects the new engine's integration.
The Faenza-based squad's engineers were impressed on Friday in Sochi by Honda's latest unit which had been fitted in preparation for the Japanese manufacturer's home race at Suzuka that takes place next week.
However, seeking better calibration of the unit and a integration with Toro Rosso's STR13 chassis, Honda decided to play it safe and return to its previous-spec engine.
"Having studied all available PU data after FP2, we realized that, although the performance was encouraging, there is still some work to do in some areas such as calibration and matching the PU to the chassis," said Honda F1 bossToyoharu Tanabe.
"We have decided to revert to the older specification PU on both cars for the rest of the weekend.
"We believe we can complete the work before the Japanese GP, so that we can run the new specification PUs on both cars from then on."
The engine's introduction on Friday means that it has been added to Honda's pool of available units and components, therefore reducing the risk of a grid penalty for Toro Rosso's Pierre Gasly and Brendon Hartley.
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