Haas team boss Guenther Steiner believes Williams and Force India, the Mercedes customer teams, have little to complain about now that Ferrari has emerged as the engine leader.

In the stretch of races prior to the summer break, the American squad and Sauber both enjoyed a strong run of performance, regularly filling at least three of the final four places in the top 10 after the top three teams.

Much of that is due to the gains of the Ferrari power unit which has surpassed the German manufacturer as the most powerful on the grid.

"Mercedes customers shouldn’t complain because they had a very good engine the last four years," Steiner told Motorsport.com.

"The first years of these regulations, if you didn’t have a Mercedes engine, you were nowhere. Now Ferrari has overtaken them and everybody having a Ferrari engine are critiqued – ‘Oh, you’ve got the good engine’.

"Yeah, we have. So did you the last four years and you didn’t take advantage of it. So what can I do? I’m very happy. If the other ones are unhappy, I cannot help them."

Renault's Nick Chester also admitted the company have been surprised by just how much performance Maranello has been able to extract with their second engine this year with some estimates between 30-40 horsepower.

"It just seems to be more power unit output," he told Crash.net. "Their straight line speeds are very strong while running a sensible rear wing on the car. So they do seem to just have good power.

“It does give us a concern. We are obviously in a pretty tight fight, so we have brought stuff all the way up to the shutdown.”

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Steiner also addressed the topic of engine regulations for the future, with the possibility of keeping the current units now appearing likely as no new manufacturers appear ready to enter.

For the Italian, he believed the important angle for customer teams is to ensure the cost of buying was guaranteed and equal regardless of where it came from.

“What I would like to have is a cost cap on the money we have to pay the engine manufacturer, that that is set and then they can do what they want," he claimed.

"If they want to make an engine out of gold, then we get it for set price, feel free to do so.

"That is more because we don’t have the expertise to get involved, V6 one turbo or two turbos, MGU-H, as long as we are sure that there is a supply and the cost of the supply is controlled whatever money we can agree on, we are happy.

"We don’t want to get involved with one or two turbos because, for me, we don’t produce one."