Mercedes team boss Toto Wolff has questioned Formula One's desire to attract new engine builders to the sport when it already has four committed manufacturers involved.

At the end of 2017, F1 outlined a vision for 2021 in which it planned to address critcism levelled at the current set of engine regulations. As well as improving the noise of the existing power units, F1 aimed to level the playing field among existing competitors and attract new manufacturers to the sport.

However, plans to simplify the current engine regulations to achieve those goals were met with opposition among existing manufacturers, who complained the rule changes would simultaneously dumb down technology and incur additional development costs. A compromise solution was proposed by F1, whereby the strict limitations on fuel usage would be opened up to improve the noise and rules forcing existing manufacturers to share technology. Such a move would be aimed at encouraging new entrants.

But Wolff, whose Mercedes team has dominated F1 since 2014 under the current regulations, said he does not understand why F1 is pursuing new manufacturers.

"Where does that thinking come from? Is it greed?" he told ESPN in a recent interview. "You want more than four? What do you want five or six? We should be happy with four premium manufacturers committed to the sport, already in there for a long time, trying to make sure that, foremost, we seek compromise with the loyal partners in there.

Toto Wolff has questioned F1's desire to attract more engine manufacturers. Eric Alonso/Action Plus via Getty Images

"And then we look at the ones who might join in the future and listen to them. But that is only the second priority."

The tweaked regulations, which will form the cornerstone of a wider aerodynamic and technical rethink in 2021, will maintain the same basic architecture as the existing V6 turbo-hyrbid engines. That will include the MGU-H -- the part of the hybrid system that works in tandem with the turbo to recover heat energy from the engine -- which F1 initially sought to remove from the power unit to save costs and simplify engine design.

Asked if he saw F1's compromise to keep the MGU-H as a political win for the existing manufacturers, Wolff said: "No, it's a purely economical factor because we have demonstrated to Liberty and the FIA that redesigning an engine is going to spiral the costs out of control.

"Even this engine [which we have agreed to] now, which has more revs, more fuel flow, more fuel allowance, will result in enormous costs. Ideally, we would have liked to stay where we are, and not touch it.

"Engine performance is converging. We see that already -- and I am curious to see where Honda are next year -- but the engines are not far away from each other. Every time the regulations change, you're going to have a wider spread between the best and the worst. So why do we change it?

"We wanted it to stay where we are and that is the compromise we've taken, but it's still going to be too expensive in my opinion."