Renault and Cosworth have written a letter to the FIA as F1 struggles to find agreement over a new engine formula for 2013.

The FIA is pushing hard for turbocharged 4 cylinder engines with exhaust-heat KERS capabilities to replace the current normally-aspirated V8s, and aiming to rubber-stamp the rules at the World Motor Sport Council in December.

Superficially, the engine makers support the sport’s ‘green’ direction but are concerned about initial costs and then a development arms race.

Germany’s Auto Motor und Sport reports that the Renault and Cosworth-powered teams last week signed a letter to the FIA pointing out the weaknesses of the proposed new rules.

They want tight limits on things including minimum weights for pistons and conrods and the entire engine unit.

“If the new engine formula becomes an arms race in turbochargers and cylinder heads, then an independent engine manufacturer will have no chance,” said Cosworth’s Mark Gallagher.

Renault team boss Eric Boullier said the French supplier will support new rules “within certain cost limits”.

“Our market in production cars is for four cylinders with a hybrid. For that reason we are not unhappy with that engine format (for F1).

“But it is about how the rules are defined. The less clear they are, the more expensive it becomes,” he insisted.

It is hoped that a cost-effective and modern engine formula might entice new suppliers, including the recently departed Honda and Toyota, into F1.

But Ross Brawn, still with contacts within Honda, said: “They’re not planning to return.”

The Red Bull flexing wing saga reared its head yet again at Suzuka.

The controversy had died down following the subsiding of the RB6′s dominance at recent races, and evidence that new FIA scrutineering tests had lessened the visible bending of the car’s front wings.

But at Suzuka, Red Bull’s dominance returned, as did video and photos showing the front wings almost touching the track.

So a reporter for the German tabloid Bild am Sonntag ventured into the FIA test garages at the Japanese circuit to observe Joe Bauer checking over the Suzuka-spec RB6.

The reporter witnessed the car lifted into the air on the test stand before 100 kilograms of weight – double the amount of the former tests – was applied to the front wing.

The RB6 passed the test, even though cynics suggest that at high-speed downforce loads, the Red Bull fails the letter of the rules.

Bauer said: “For that (test), we’d have to build a wind tunnel at each track!”

Indeed, if those downforce-like loads were simulated with mere scrutineering weights, the clever Red Bull wing design would likely break.

The RB6 also passed the FIA’s more stringent 300kg underbody test at Suzuka.

Red Bull and Ferrari hit back at McLaren on Friday as the flexible wing saga continued to run.

It is the British team that has been the most vocal about the wings on the Red Bull and Ferrari cars this year.

But technical bosses Adrian Newey and Aldo Costa told reporters at Monza that they were ready to agree to an even more stringent flexibility test — and it was McLaren that turned it down.

“We are happy to further increase the stiffness if we want a front wing that is double the stiffness,” Ferrari’s Costa said.

Currently, when weights are placed on the front wings during pre-race FIA scrutineering, the permissible deflection is 10mm.

“It was discussed in the technical working group to have a 5mm deflection, but also engineers who are at this table didn’t accept,” said the Italian.

Also with McLaren’s engineering director Paddy Lowe at the table, the discussion was taking place during the FIA press conference.

“I think it was Paddy who suggested (the test stay at) 10mm,” said Red Bull’s Newey.

Costa admitted he has been frustrated by the entire saga.

“I don’t know why this saga has been created,” he said.

Newey agreed: “The test has been as it has been for several years and suddenly there is a load of excitement.”

Red Bull is using an unchanged front wing at Spa-Francorchamps, but the floor of the RB6 might soon have to be tweaked to satisfy tougher FIA scrutineering tests.

The front wing flexibility test was altered for Belgium, essentially to ensure that wings are bending downwards only in a linear fashion when weights are proportionately applied.

Red Bull boss Christian Horner said these tests had not necessitated a design change since the car dominated in Hungary, but it has emerged at Spa that the FIA also has its eye on other aspects of alleged flexing.

It is believed that the RB6 is getting its front wings so close to the ground also due to having a bendy floor.

Tweaked floor flexibility tests, and new rules stipulating the amount of breaks or joins allowed underneath the cars, will reportedly be applied as of the Italian grand prix at Monza next month.

“I cannot say whether we will be affected more or less than any other team,” said Horner on Thursday.

Germany’s Auto Motor und Sport said the existing floor tests involved applying 200 kilograms to the front of the floor, allowing flexibility of no more than 5mm.

At Monza, the new tests will reportedly involve additional loads being applied now at several locations underneath the cars.

“Webber said in an interview a couple of weeks ago that if you have a very special device on the car, people should have to build their own.

“I didn’t know they had a device on the car, so there you go,” said McLaren’s Jenson Button on Thursday.

“We’ll see what happens here, and we’ll see how their pace is compared to us,” he added.