Norris and Piastri took second and fourth respectively in the recent British Grand Prix.
It was a breakthrough result for McLaren and its upgrade package after struggling through the first half of the season, but it was also big boost for rookie Piastri, who took his best result in F1 by some margin.
The highly rated Australian has repaid the faith shown in him by McLaren when it went to great lengths to prise him away from Alpine last summer, and according to team principal Stella the 2021 Formula 2 champion has also had a positive impact on Norris.
"Oscar's performance is just outstanding, if you think he's a rookie," Stella said. "And right away, even in practice, he was immediately quick.
"This allows also some synergies between the drivers because both can see where you can improve from each other. And this elevates the performance of both drivers.
"So, not only we are impressed, but there's a net benefit in having two competitive drivers because both can benefit."
After a year on the sidelines as Alpine reserve driver, Piastri's race craft was identified as a potential area of improvement.
Source: Autosport