Jenson Button says the updated Honda engine being run in his McLaren this week is the biggest step in performance the Japanese manufacturer has made since its return to F1 last year.
McLaren and Honda struggled for performance and reliability in 2015, forcing a rethink of the power unit over the winter. The resulting engine has been testing in Barcelona this week and Button is impressed by the step Honda has made.
"I would say it's the biggest improvement that I've felt with the power unit over the last 14 months, which is good," he said. "I think the improvement is good but obviously we're still a long way off of the other guys and you can see that in the speed traps. But you can definitely feel the difference in the initial part on the straights.
"I think the important thing is we're able to do quite a few laps, we were held up a little but by a few little niggly things today and some red flags but I felt that we could have done a lot more laps today and I think it shows the reliability, which is really important. We've got that sorted I think, fingers crossed. So we can really, really push the performance with the power unit and that is what is happening.
"We're not close to Melbourne spec yet, there's a lot more bits coming. Hopefully this week and some more in Melbourne for P1."
The main issues last year were related to inefficiencies in the design of the power unit's turbine and MGU-H. The result was limited deployment of hybrid power over a lap, which had the potential to leave the car with a deficit of over 160bhp on some of F1's longest straights.
"The progress is massive in that area," Button added. "That's something we knew we had to work on. Deployment is not something we could have worked massively on last year with the compressor but over the winter we've been able to and Honda have done a great job in terms of bringing that to testing.
"We've had no reliability issues with it at all and it's a big difference. On some circuits in a race we were losing 0.6s last year every lap because we didn't have deployment. Now the system's working well and I think from here on it's marginal gains really compared to our competitors. So it's a good step forward and a necessary step forward.
"In qualifying there was probably 0.1s or 0.2s because we couldn't deploy even through a qualifying lap for the whole lap. Now we can easily, so it's a good amount but there's still a lot more we need to do to really be competitive in every area - with the power unit, with the car itself aerodynamically we've still got a long way to go until we're properly competitive."
Despite the progress, Button is still playing down expectations ahead of the first round.
"I have no targets. My only target is to push, to give it our all, give our maximum and we'll see what the results are. There's never a positive of me setting a target right now because as a positive person you're always going to target higher than possibly maybe you can achieve, and then you just get knocked down by other people, so it's not worth it.
"I'm hoping we won't be hanging off the back of the field, but there's still a lot of work before I feel that we are properly competitive, yeah. There's still a lot of work needed over the next two days to find a set-up that really works for us because we're not there. So a lot of work still needed."