Having run a new-spec power unit in the Toro Rossos of Pierre Gasly and Brendon Hartley in Russia on Friday, Honda have decided to move both cars back to the previous spec for the remainder of the Sochi weekend.

    Despite positive signs after Friday’s practice sessions, Honda stated that "having studied all available power unit data after FP2, we realised that, although the performance was encouraging, there is still some work to do in some areas such as calibration and matching the power unit to the chassis."

    Honda will continue to work on the new spec, which they expect to have ready in time for race use on both cars at the Japanese firm’s home Grand Prix in Suzuka next weekend.

    Gasly and Hartley will still be required to start from the rear of the grid on Sunday – they are expected to form the penultimate row ahead of their Red Bull stablemates – due to the previous engine changes in Russia, but should not pick up any further penalties in Japan.