Mercedes and Renault have admitted to being sceptical about Formula One's proposed new power units for 2021.
A vision of F1's future is starting to emerge after the FIA and FOM outlined their plans for the sport's next set of engine regulations, with emphasis placed on improving the quality of racing, reducing costs, and producing better sounding power units for 2021 onwards.
The proposed specification would see the controversial 1.6-litre V6 turbo power units currently in use kept, but they would become simpler by replacing the complex MGU-H -- one of the two hybrid elements that recovers heat energy from the turbo -- with a more powerful MGU-K. F1 is also aiming to provide an attractive proposition to potential manufacturers looking to enter the sport, while holding the interest of the manufacturers already involved.
However, Mercedes boss Toto Wolff said the Paris presentation did not go down well with any of the current engine manufacturers and was surprised the FIA revealed so much information about the plans for the new engine, after being told that the proposal would be subject to further discussion and amendments.
"This is their vision and proposal and we haven't accepted it," Wolff told the BBC. "The flaw of the concept is that it's a completely new engine and new investment. It portrays it in a way of this is how we're going forward and none of the current OEMs (car manufacturers in F1) was particularly impressed.
"The new concept needs to tackle the deficit that has been outlined -- development costs and noise level -- and all that needs to be linked with a global view of F1. We haven't seen any of that."
Renualt Sport manging director Cyril Abiteboul echoed Wolff's comments and said Renault is against being "presented with a new engine on which we would have to make substantial development and substantial financial commitment without an understanding of the broader picture of what F1 would look like past 2020.
"I'm referring to not just engine regulations but chassis regulations as well as the commercial side of F1," he added. "I approve of the targets that have been set in terms of cost, noise and power, and the fact we need to try to make performance continue to converge. Those are things that could have been done with the current engine architecture anyway."
Abiteboul added he is unsure whether the new rules would be successful in attracting new companies.
"I don't see how what has been presented would be offering a model for an independent engine manufacturer," he said. "Maybe it would lower the cost of access for a car maker, but you would still need a substantial amount of marketing dollars to spend into research and development to make any business plan work for the new engine.
"And that is actually our problem, that we need to spend again, just like a new entrant would have to spend. But I don't think an Ilmor or a Cosworth will be able to go for it independently without the subsidises of another car company."
Abiteboul said he is also sceptical about the proposed removal of the MGU-H, one of the most expensive elements of the current power units.
"My problem with the removal of the MGU-H is that as soon as you do that it is a new engine," he explained. "It fundamentally changes the way the energy is managed within the engine, the way the turbo is working and so on and so forth. It is a new combustion concept, a new way to manage turbo lag and efficiency, so it is new design of turbo."
It remains to be seen what Ferrari and Honda make of the change, with both yet to comment following Tuesday's meeting.