The flaring up of a dispute between manufacturers over Formula 1’s 2026 engine rules has inevitably triggered doomsday fears about its potential impact on next season.

There has been hype that the start of the year could be overshadowed by a protest lodged against Mercedes and even Red Bull at the season-opening Australian Grand Prix.

Another outcome that has been mentioned, with sources suggesting that the gains available from exploiting the fuel compression limit could be worth as much as 0.4 seconds per lap, is that the title hopes for anyone not doing it are already over.

This is especially true because, with power unit homologation restrictions in place and the nature of work needed to change fundamental engine architecture so complicated, a recovery is something that can only be properly executed for 2027.

But there is another viewpoint that the whole compression ratio controversy is a classic Formula 1 storm in a teacup, and that the nightmare scenario of the season already being a write off for some (at least those not powered by Mercedes and Red Bull) is something that will not be seen in reality

After all, everything is theoretical right now. 

Nobody knows for sure exactly how much benefit Mercedes and Red Bull have got from what they are doing - no engine has run against another on track yet - and there is no guarantee that any power gains made will even be critical to success on track.

Furthermore, it is argued there is plenty of scope in the regulations for those manufacturers that have not exploited things to be able to catch up – even within 2026 – to not only negate any advantage Mercedes and Red Bull have early on, but even leapfrog them.

The truth of the situation is likely somewhere in the middle between the different viewpoints.

But this does not mean that the issue isn't going to dominate chatter ahead of the start of the season, nor stop it exploding at the Australian GP if things do end up being towards the worst end of fears.

So let’s take a look at some of the key issues and try to piece together estimates of where things go from here.

What is being disputed in the regulations?

The entire matter revolves around a new limit that was brought in for 2026 regarding a maximum compression ratio.

The article at stake is C5.4.3 which in full states: “No cylinder of the engine may have a geometric compression ratio higher than 16.0. The procedure to measure this value will be detailed by each PU Manufacturer according to the guidance document FIA-F1-DOC-C042 and executed at ambient temperature. This procedure must be approved by the FIA technical department and included in the PU Manufacturer homologation dossier.”

The fuel compression ratio had been set at 18:1 in the previous rules set. It was reduced to 16:1 (officially defined as 16.0 in the regulations) for the 2026 rules as part of an effort to help attract new manufacturers, as it was a much easier target to hit.

While the rules state that “no cylinder of the engine may have a geometric compression ratio higher than 16.0”, the reality of F1 is that this is one of many regulations where compliance is verified when the car is stationary in the garage.

To ensure this particular rule is being followed, the FIA validates things through measuring the volume differences in the cylinder between when the piston is at its lowest point and when it is at its highest point. This allows it to work out what the compression ratio is.

That is not something that can be done accurately when an engine is running at 15,000rpm and out on track.

Furthermore, normal thermal expansion of parts means that there will always be some change between a compression ratio when an engine is cold in the pits and when it's at full operating temperature on track.

So, from Mercedes and Red Bull’s perspective, the measurement that has always mattered has been the one taken by the FIA as a reference when the checks are made.

Therefore, as long as the engine fully complies with the wording of the regulations for the checks when cold, then that is all the rule says. 

Their argument is that it is not even a loophole that is at play here; it is simply what the rules state in black and white.

The FIA emphasised last week that what counts is when the checks are done.

A spokesperson said: "The regulations clearly define the maximum compression ratio and the method for measuring it, which is based on static conditions at ambient temperature. This procedure has remained unchanged despite the reduction in the permitted ratio for 2026."

Having a rule stating a limit for checks when it is stationary, and the car being in a different state when out on track, is not unusual.

Moveable aerodynamic devices are theoretically banned but we all know the wings flex when they experience forces out on track. Tyre pressure compliance comes from the readings that are taken when the car leaves the garage.

From the viewpoint of the other manufacturers, however, the argument is that the 16.0 limit laid down in the regulations is a hard stop – especially because it has its own standalone sentence.

It is clearly stated that: “No cylinder of the engine may have a geometric compression ratio higher than 16.0.”

So, taken in conjunction with Article C1.5, which states that “Formula 1 cars must comply with these regulations in their entirety at all times during a competition”, the argument is that anyone operating with a compression ratio above 16:1 when out on circuit is in breach of the rules.

It is clarification over the latter that is believed to be central to where things go from here, and whether or not there could be a protest lodged.

What is this advantage worth?

Ferrari, Audi and Aston Martin/Honda clearly feel that the issue is a significant one, which is why it is understood they have written a joint letter to the FIA asking for answers over some of the key aspects of what is going on.

Their concerns are prompted by two key consequences: the immediate performance impact and the long-term prospects of making up any lost ground.

While nobody outside of Mercedes nor Red Bull knows exactly how much performance they have found from what they have done, The Race has learned that some recent simulation testing has exposed the kind of big potential that an increased compression ratio offers with these new regulations.

Based on some evaluation studies, one high level source has suggested that increasing the compression ratio of a 2026 F1 engine from 16:1 to 18:1, offers an uplift in performance of 10Kw – equivalent to 13 horsepower.

Extrapolating that to early predictions for the 2026 F1 cars, it is estimated that the laptime benefit of this varies between 0.3-0.4 seconds per lap depending on the track. 

At some tracks that are more power sensitive, a 10kW boost will deliver in the upper range of that gain, while at other venues where power is not so critical, it will be the lower range.

But even at circuits where extra power does not help much, the performance gains could bring benefits in terms of improved fuel efficiency which can then deliver a bonus in terms of a lower amount of fuel (and therefore weight) a car must carry.

What is not known, however, is just how much Mercedes and Red Bull have managed to raise the running compression limit over 16:1, and how close they have got to the 18:1 of the previous rules set that was near the limit where you want to be before problems like engine knocking become an extra headache.

So have they done it perfectly and managed to unleash that full 10kW on offer; or have they just found a fraction of it?

The answer won’t be known at least until cars start running in anger for the first time, and even then, the true picture may not be clear because there are a host of other factors that determine engine performance.

Rivals can't catch up until 2027?

With manufacturers currently in the process of manufacturing and constructing their race one engines, there is nothing that Mercedes and Red Bull’s rivals can do in terms of countering things with a fresh design direction in the short term.

In theory the homologation of the power units does not take place until March 1, but in reality, it is already too late to do anything different before dossiers have to be submitted to the FIA.

So what each engine manufacturer has right now is what they are going to start the year with and have to live with.

Unlike teams finding out that, for example, a rival has found a clever aero trick that can be copied and brought into play in a matter of weeks, fundamental changes to engine concepts are slow-burning projects.

And this not only comes because of the complications of rethinking and proofing new architecture, but on top of this, Mercedes and Red Bull’s rivals will need to fully understand exactly how the two teams have achieved what they have done.

As ex-F1 technical director Gary Anderson referenced this week, a thermal expansion that pushes the surface of an 80mm diameter piston just 0.5mm closer to the top of the cylinder would be enough to move from a 16:1 ratio to 18:1. 

That may not sound a lot, but with engine rules heavily restricting the use of materials, delivering that expansion is still very complicated.

Sources have indicated that any modification to the power units to properly exploit the compression ratio limit to the maximum would be something that would take many months and probably not something that can be realistically done until the start of the 2027 season.

There is potentially a window that gets opened up earlier, though, for modifications to be made if one of the manufacturers is well behind the benchmark engine.

As part of what is known as additional development and upgrade opportunities (ADUO), the FIA is going to monitor engine performance over three phases of 2025 as part of an effort to ensure that nobody falls too far behind.

There will be three periods - races 1-6, 7-12 and 13-18 - and at the end of these periods a manufacturer eligible for extra development can implement further upgrades, extend the usage of their test benches, and adjust their cost cap spending to accommodate it.

So if a manufacturer is a set performance chunk off the best power unit after the Miami GP (round six), then the door will be open for them to introduce a new homologated ICE, which could in theory have a different compression ratio.

If the FIA deems a manufacturer to be between 2% and 4% off the best, then they will be allowed one additional upgrade; if they are more than 4% off then they will get two upgrades.

What is not known, however, is whether it would be possible to introduce an overhauled ICE for the second half of 2026 that exploits the compression ratios to the max, or if it will take longer, even if someone were allowed to do it.

What's next?

Meetings have been ongoing with all the manufacturers and the FIA to keep discussing the 2026 regulations – and a response to the letter from Mercedes’ and Red Bull's rivals to the governing body will likely follow at some point.

However, the way that the fuel compression rules have evolved – and make it explicit that checks are conducted at ambient temperatures – it seems that the FIA has doubled down on there being no ambiguity about its stance.

As long as it is satisfied that the procedures to check the compression ratio at ambient temperatures are followed, then that is it as far as its involvement needs to be.

Mercedes has been in dialogue with the FIA throughout the rules process so there is no element of it having tried to sneak something through.

It has had reassurance that its interpretation of the rules is in line with the FIA so it has kept pursuing its design process.

For the FIA to change something suddenly now for the start of 2026 – like for example, demanding that the checking process be revamped to be based on when cars are under hot conditions – simply because some entrants have not exploited an area of the rules, would be wrong.

The FIA did suggest last week that “if necessary adjustments to the regulations or measurement procedures can be considered in the future”.

However, this is very much likely only going to be something in play for 2027 – and one that would need to be done transparently and in a manner that was fair to all.

One suggestion that has emerged amid the discussions over the matter is, for 2027, to either revert to the 18:1 ratio or get rid of the limit totally, so teams all know exactly what they are operating to.

Protest threat

For those engine makers who have not exploited the fuel compression possibilities, the choices now appear quite simple.

They either accept that they have missed a trick, and they get on with working on a solution that they can introduce as soon as possible, even if that means effectively writing off their 2026 title hopes.

Or they can decide to go all in and challenge the rules, potentially with a protest in Melbourne. But that risks opening up a can of worms when it comes to the compliance of cars when running out on track.

Last week, Ferrari team principal Fred Vasseur voiced his concern about there being some "danger" in the new rules about grey areas being exploited.

“Teams have grown up massively over the last year, and it means that we have more and more people trying to find loopholes,” he said.

“But I think we have also to put ourselves on the FIA's side. I think it's also a huge challenge for them to not arrive in Australia or in Bahrain and to have someone exploiting a loophole into the regulation.

“If it's a good job on the regulations and someone is able to do a good car faster than the others, I think it's fair enough. But if it's a kind of loophole in the wording and so on, it's much more difficult for everybody - and much more dangerous for F1.”

Whether the fuel compression trick is a good job or a wording loophole depends on which side of the fence you sit right now, but it’s a debate that is going to rage on for a while yet.