Formula 1 motorsport director Ross Brawn has revealed a new agreement aimed at attracting new engine suppliers into the sport.

Planned changes to the power unit regulations for 2021 have been largely watered down as possible entrants like Porsche and Aston Martin walked away leaving just the current four manufacturers, Mercedes, Ferrari, Renault and Honda.

However, based on lessons learnt from the Japanese company's initial tough start to life on the grid, after returning with McLaren in 2015, a compromise of sorts has been reached.

"The drawbridge has been pulled up and the existing suppliers don’t want anyone else to come in," Brawn initially told Formula1.com.

"We have found a compromise. There are regulations coming out which would mean new entrants will get support from existing entrants. There will be components and technology which will have to be shared if it is requested.

"It is not quite such a radical change that we were proposing, but still quite a good step in the right direction and there are some nice changes to the way the driver has to manage the engine, which I think goes a long way in the sporting direction.

"There has been a recognition from the existing manufacturers that they can’t shut the door behind them," the former Mercedes boss noted.

"If we start to get serious interest from another manufacturer or supplier, they have to cooperate to find ways of helping that manufacturer come into F1."

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Another big negotiation with the manufacturers and some teams is the proposed budget cap of $150m per year which is aimed at closing the equality gap between the top teams and the rest.

"We are having pretty constructive discussions with the teams," Brawn claimed. "Unlike previous initiatives, this budget cap is going to be embedded in the regulations of the sport.

"The fairer distribution [of revenues] among the teams is balanced out by the reduction in costs particularly by the big teams, so their bottom lines will be improved.

"If we follow the budget cap proposals, I can’t see a team in F1 which won’t be better off."