Ferrari drivers, Kimi Raikkonen and Sebastian Vettel, were keeping a lid on their expectations despite a strong first day for the Scuderia at the Belgian Grand Prix.

Both men led a session apiece at Spa-Francorchamps with the Finn setting the quickest time of the day in the afternoon, a 1m43.355s, to finish just over a tenth-and-a-half clear of Lewis Hamilton's Mercedes.

One of the key stories being followed is the relative gains of the new 'Spec 3' engines both leading teams have brought to Belgium, but both men were reserving judgement.

“Obviously we never put in the car anything we don’t think is a bigger step forward or better so it’s not possible to say," Raikkonen said.

"It’s not a night and day difference ever, otherwise you could see by yourself if that was the case."

Vettel added: "We’ll see what the next two weeks bring. For now, everyone seems quite happy that the engine is doing what it’s supposed to do. 

"It is only Friday so you cannot tell anything. Let's wait until tomorrow."

The German would also appear to have some work to do after errors on both his qualifying simulations left him down in fifth.

"Kimi maybe was a bit happier on one lap but we still have a bit of time," he said. "The car felt not yet where I want it to be. We have a bit of margin [but] there’s quite a bit more in the car. I need to make sure I get to it tomorrow.

"Here it's important to be confident to get the right timing as there isn’t much time to think when to turn in and so on because the cars are quite fast.

"It needs to click. On one lap, it didn’t click but overall it’s going in the right way."

A worry Ferrari might have is the possibility for rain over the weekend at Francorchamps, something that has prevented them from taking victories at the last two races.

“I think we had our weaknesses in the wet but we have worked on those," he admitted. "We understood those so if we have wet conditions it will be quite nice to confirm and see whether we found the right things.

"On this track everything seems to happen faster, so it should be a lot of fun and if we have dry conditions tomorrow for qualifying, we should be okay."