F1's manufacturers have joined the sport's commercial rights-holder Bernie Ecclestone in expressing their opposition to the FIA's intention to overhaul the engine regulations for 2013 - but Jean Todt remains adamant that the governing body will not budge.

Ecclestone has slated the plan to replace the current 2.4-litre V8 powerplants with 'greener', turbocharged, four-cylinder 1.6-litre units from 2013 onwards - primarily to underline the fact that F1 is taking its environmental duties seriously - as 'a joke', and after Ferrari had already agreed with the British billionaire, other manufacturers are now similarly confessing to their misgivings about the proposals.

"The FIA made its decision based on false assumptions, without considering the side-effects," Formula One Management (FOM) chief executive Ecclestone told Swiss newspaper Blick. "The manufacturers and the teams need to go to the FIA and say they have thought about it and concluded that while the decision seemed right then, from today's perspective, it is wrong."

The manufacturers' argument is reportedly that they cannot afford to build competitive four-cylinder turbocharged units by 2013, with Mercedes-Benz Motorsport Vice-President Norbert Haug telling Auto Motor und Sport that 'we support the four-cylinder only if there is a guarantee that the costs will be reduced by 30 per cent over a period of five years', the German fearful that should Renault withdraw, the Stuttgart-based marque may find itself having to supply even more customer teams.

Lotus Renault GP managing director Eric Boullier has similarly mused in an interview with the official F1 website: "The question is, can we afford such a change? All-in-all, it is important that we don't take the wrong decision in terms of the sport's fans and its future."

It has also been suggested, claims SPEED.com, that the Craig Pollock/PURE interest in the new regulations was merely a convenient political coup in an effort to demonstrate that the turbo formula is capable of attracting new manufacturers, after the likes of Honda, Toyota and Volkswagen all seemingly dismissed the notion that it may entice them to join the grid.

Ecclestone insists that sticking with the already well-proven V8 formula is a no-brainer, and the 80-year-old hinted over the Spanish Grand Prix weekend in Barcelona that FIA President Todt may be softening his approach and preparing to make some concessions [see separate story - click here] - but after meeting with the sport's engine manufacturers on Saturday, the Frenchman reiterated that the new rules are proceeding full speed ahead.

"As I said before, we will not change [the 2013 regulations]," he told French motoring blog Auto Plus. "You can do something else, create another discipline, but the FIA Formula One World Championship will take place with the engine regulations that have been decided."

Meanwhile, after it was mused that Renault had come around to the same way of thinking as Ferrari and Mercedes, the French marque's F1 managing director Jean-Fran?ois Caubet stressed: "We are fully supporting the FIA. It makes a lot of sense for a carmaker like Renault to be road-relevant. I think it is a key point for the future of F1."