Sebastian Vettel, the fastest man around the Circuit de Catalunya, says Ferrari needs to extract more performance from its SF71-H.
Vettel topped the timesheet on Thursday, putting 185 laps and a new unofficial lap record on the board. But according to the German, while reliability was impeccable, more pace is required.
"We still need to work on the performance and the feeling," said the four-time world champion.
"In terms of reliability it was rock solid, we didn't have any major issues or major concerns, so hats off to all the guys in the factory."
Vettel went for a race simulation in the afternoon session but was left uncertain about his relative performance among the front-runners.
"Pretty happy. We got a smooth run, car-wise no issues, no red flags, so we could get through, and also for the guys I think with the stops. So that was solid," he said.
"I don't know in terms of pace. You always think that you could have done better here and there, just like racing, but I think it was OK. Mostly we did a lot of laps.
"After the race sim we still did a good chunk of laps. That's important in understanding the car. There are some things we still need to get on top of. So it was important to run."
The Scuderia stalwart concluded his pre-season testing work today, as Kimi Raikkonen takes over for tomorrow's final session before everyone heads off Down Under.
Ultimately, Vettel leaves Spain well with the impression of a job well done and a better undestanding of his mount.
"You always hope for more. It's the same for everyone, especially the first week, losing time, but all in all I think it was good, the days that I had," he added.
"And I'm not going to get more, so that's it, and I'm pretty happy with the laps I had with the feeling I got for the car, which as I said improved.
"We understood it a little bit better. We still have some stuff to understand, which we're not sure about, but it's normal.
"The track's different, the surface is different, makes it a bit hard to compare. But it feels like a step forward. I think it's probably making sense.
"I think it all depends where the others are, and well find out in the next couple of weeks."