Red Bull team boss Christian Horner has used his team's lack of performance at Spa-Francorchamps to justify the decision to switch to Honda in 2019.

Even though Max Verstappen claimed a podium at his defacto home race, the RB14 was a long way off Mercedes and Ferrari as they had to give up speed through the corners to run less wing in the hopes of nullifying the top speed disadvantage.

A new Spec 3 Renault engine is to be introduced this weekend, with both Red Bull drivers taking it and estimates it will provide a third of a second in performance this weekend at Monza, even so, Horner remains convinced Honda is the way to go.

“Yeah, I mean we need to make a step,” he told Sky Sports. “You can see the gap to Ferrari and Mercedes… you just heard Lewis [Hamilton] moaning about Ferrari, I nearly got my violin out.

“You know, the gap is significant and I think if we can just close that.

“Honda are making great progress. You know, they [Toro Rosso] are scoring points regularly and Pierre [Gasly] has been very upbeat about them and you can see they are making headway.”

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Indeed, the soon-to-be Red Bull driver was pleased with what he considered an unexpected ninth-place finish at Spa, which included a strong battle with the Ferrari-powered Sauber of Marcus Ericsson.

"It was supposed to be a difficult weekend for us on a track like this, and to end up with two points is really positive," said the Frenchman.

"I think everything is getting better, you know. The drivability, reliability, we don’t have any issues. We just need to get that extra performance to make us more consistent inside the top ten, but I think this weekend was really positive.

"I think next weekend will be a tough one but just looking at this weekend, it was good."

The Japanese manufacturer is also likely to continue their development push until the end of the season, with Toro Rosso willing to tolerate more engine penalties for more performance.

"You know what drivers are like, the more power they give us, the happier we are. I know we will have a couple more upgrades coming before the end of the season, but Honda is pushing flat out," Gasly added.

"To score points on a track like this is positive for the team."