Red Bull boss Christian Horner fears that there is no way for Renault and Honda to close the engine performance gap to Mercedes and Ferrari under the current regulations.

Horner said that the situation won't change until the next major overhaul of engine regulations for 2021. Until then, in his view Ferrari and Mercedes will likely continue to dominate the sport.

Currently, the three Mercedes-powered teams on the grid have a total of 603 points in the constructors championships. Ferrari's stable of teams have 413 points, compared with the Renault line-up on just 286 points. Handicapped by having only the one works team, Honda has amassed just 11 points so far in 2017.

"Those two manufacturers have such a march, such committed investment," Horner told Sky Sports F1. "It's difficult to see how the others will catch up in the intervening period between now and 2021.

Not that Horner was throwing in the towel. Red Bull demonstrated that it could carve its way through the field with a storming performance by Daniel Ricciardo at the Italian Grand Prix.

"We'll never accept that we can't be competitive," Horner insisted. "We'll keep pushing and keep developing and try and make up whatever horsepower deficit there is on the chassis side."

However there was nothing Ricciardo could realistically do when it came to the two works teams at the front. And reliability continues to be an issue for both Renault and Honda.

The current situation has made Horner even more convinced that that the sport is heading in the wrong direction with its current regulations.

"This engine has done nothing positive for Formula 1," he complained on the grid at the Italian Grand Prix.

Horner says he hopes that the next iteration of engine regulations will make power units cheaper and less complex - and more reliable. If that happens, more manufacturers might decide to return to the sport.

I think there are iconic manufacturers who would be keen to come in if it was affordable," Horner said. "Aston Martin being one of them, Lamborghini attending meetings.

"Manufacturers have always come and gone in Formula 1 whenever it's suited them. I think the most important thing is to get the product right, get the show right. Then it's up to the manufacturers to be there or not."

Horner conceded that Formula 1 might lose some existing manufacturers if the rules are changed too radically.

"We may well do," he said. "[But] so long as you have Ferrari there, so long as you have historic teams like McLaren and Williams and so on, and other manufacturers like those I've mentioned were to come in.

"It's all about the spectacle," he concluded.

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