Last weekend, at Sochi, Honda introduced its latest-spec power unit. It was only used in the Friday practice sessions - both drivers giving it the thumbs up in terms of increased power - before Toro Rosso reverted to the older-spec unit in order that the upgrade could be raced this weekend - at Honda's home race - without penalty.

The upgrade unit will form the basis for the Japanese manufacturers 2019 unit, therefore progress will be closely followed not only by Toro Rosso but 'big sister', Red Bull.

The Faenza outfit's boss, Franz Tost, is under no illusions as to what he expects from the upgrade.

"With the spec-3 engine we must be in Q3 and we must stay ahead of Sauber," he said, "because they put a lot of pressure on us in the Constructors' Championship. That's the target."

"Regarding this season, we were not as quick in the development as we would have wanted to," admitted Honda's Masashi Yamamoto. "However, recently, everything has been much better, especially regarding the combustion chamber. We have upgraded it, and it's finally complete, and very successfully complete.

"Regarding Russia, and the problems we had with the other engine," he continued, "it had regard to the calibrations but we have fixed it since Russia, and within this one week before the race in Suzuka, we have fixed that issue and so I suppose Mr Tost can look forward to great weekend."

Asked about the positive comments already coming from Toro Rosso and Red Bull, Yamamoto added: "Regarding Spec-3, which we have brought in Russia, as you know, it hasn't raced yet, so it will be the first opportunity to race with the new spec.

"According to the results that we'll have after the race, it will be more comparable. We can start comparing data with the other ones that we have used before. So, not only the engine but of course the entire performance with the car."

While Pierre Gasly was sidelined for much of FP2 with a fuel system issue, Brendon Hartley finished 10th on the timesheets and said he was pleased with the pace, and drivability of the upgraded engine.

"Honda worked very hard on the dyno by improving the mapping and calibrations since Russia," added chief race engineer, Jonathan Eddolls, "and these changes have all worked as expected.

"The drivability and performance of the latest PU have improved," he continued. "FP2 was a smooth and productive session for Brendon, the balance was better and he extracted a good lap from the car."

Check out our Friday gallery from Suzuka, here.