Renault-powered teams face a longer wait for performance improvements in 2015.
After a dire start to the season for the French manufacturer, boss Cyril Abiteboul said after Canada that with reliability now under control, Renault can finally turn its attention to power.
But until a better engine arrives, Red Bull and Toro Rosso are trying to compensate with their respective chassis.
"We try to do everything we can with the wings when there are many straights, like in Canada," Toro Rosso rookie Carlos Sainz told the Spanish sports daily Marca.
"But even that does not completely fix the top speeds. We are missing a lot" of performance, he added.
Sainz admitted he does not expect performance improvements "until Spa", referring to the Belgian grand prix that takes place after the August break and forthcoming races in Austria, Britain and Hungary.
Dr Helmut Marko, the prominent Red Bull official, confirmed that Renault is currently working on performance improvements.
"Yes, there are some steps coming," he told F1’s official website, "but the results have to be seen — if it works, then at best (it will arrive) at the last three races.
"We have to be patient. In three weeks from now we should know if the new project, which is on the dyno now, is working or not," added Marko.