"It had been a strong weekend. Not really much to show for it unfortunately," Hartley told crash.net.
"I'm still pretty positive for Montreal. We have an engine update coming, and we had a new floor here so we had some performance to put on the car. It looks like the team is really starting to unlock the car's potential."
Next weekend's Canadian Grand Prix will see Honda unveil its first engine update of the season where it is expected there will be significantly more power available.
Until now the Toro Rosso has struggled compared to rivals on long straights or high speed circuits. That could be a thing of the past with testing indicating that weakness will at least put the Honda-powered car on a par with other teams if not better than some.
"I don't know exact numbers, I think it's better you ask someone from Honda or Toro Rosso," Hartley said.
"But I think it's meant to be a sizeable step," he admitted.
The Montreal track is one suited to power with a couple of long straights featuring in the 4.36km long Circuit Gilles Villeneuve and will give the new Honda engine an instant assessment.