Kimi Raikkonen admitted his opening day of practice in Sochi was frustrating as he put Ferrari's new engine upgrade through its paces for the first time.
Ferrari has introduced its first in-season engine upgrade for Sochi this weekend but Raikkonen has been keen to play down its significance. Friday practice is rarely a fair indicator of true pace and Raikkonen thinks making accurate comparisons are difficult.
"It was a difficult day," Raikkonen said. "Nothing seemed to work as well as I wanted. One of those days struggling to make the tyres work and making sense out of the set-up. Apart from that everything was more or less okay."
Speaking about the upgraded engine, he said: "It is the same, no real change. We are testing some things ... It is a new engine. Comparing a new engine to the same [old] engine is very difficult to say. It feels different in different places and different days. It works well, and we wouldn't use any new parts -- engine or any other -- if we don't think it is a good thing."
Ferrari remained some way off Mercedes in both sessions, including the qualifying simulations in FP2, and saw Sebastian Vettel's car break down with what is believed to be an electronics issue. As always, Raikkonen is paying little attention to the headline times.
"I haven't seen the lap times really. It's not an ideal day, but on my side I think we have to work because the other car didn't run. I didn't get any good proper laps, but this is a practice day. I am sure we will find something tomorrow."