Mercedes team principal Toto Wolff says the Silver Arrows' engineers have suffered a "setback" in their power unit development for 2019 as the five-time consecutive constructors' champions try to maintain position ahead of Ferrari in Formula 1's development battle by lifting their ambitions.
Domination of the V6 Hybrid era continued for Mercedes in 2018, with a fifth constructors' crown added to Lewis Hamilton's triumph in the drivers' championship.
However, the campaign was not plain sailing for Mercedes and Ferrari's ability to unlock extra pace through the deployment of harvested energy put them on the back foot in the middle part of the season, only for errors from Sebastian Vettel on the track and the Scuderia on the pit wall to let them down.
Wolff says murmurings on the F1 grapevine have prompted Mercedes to raise their sights for next year, but it is pushing the team to its limits.
"There is a tremendous development race that is happened as we speak," Wolff said at a sponsor event.
"Finding downforce, reducing drag and of course the engine is a very important part, adding more horsepower to the engine.
"So we are setting ourselves really ambitious targets. We have actually increased the targets six weeks ago because we heard some rumours that others were doing well.
"We've had a little bit of a setback on the engine side where we believed the new concept would deliver a little bit more. But these guys are very ambitious like all of us and so I'm optimistic.
"We will know when the first qualifying session gets underway in Melbourne, this is the moment where everybody shows their cards."