While Formula 1's focus right now is on nailing rule tweaks in time for the Miami Grand Prix, the next political battleground is already on the horizon.

It revolves around engine upgrade allowances for this season and beyond and has become a hot topic between manufacturers and the FIA.

After the Miami race in May, the FIA will define its index of who has the best engine and who is far enough behind to be allowed to upgrade. Ahead of that, interest in the decision-making process and any potential outcome has been bubbling away.

A fascinating dynamic is in play, because there are some differences of opinion in the paddock about how things should play out - and that means inevitably an increased focus on what the FIA will do.

Manufacturers are not all lined up on how they see the pecking order, with suspicions rife of potential sandbagging games.

Plus there have been differences of opinion among them about how the methodology and measurements should be done to come up with the ranking, although in the end it is down to the FIA on how it decides to do things.

The most likely scenario remains that Mercedes will emerge from the analysis as the benchmark, with everyone else other than Red Bull getting some green light for development.

But that is not for certain, as there are some questions about whether Ferrari is actually better than it looks.

And there are even wild rumours of a twist in this whole engine process; that Mercedes could be in the group that gets the green light for improvements as it is another manufacturer that actually has the best engine under the definition the FIA will use.

What the rules say?

As part of the new ruleset for this year, the Additional Design and Upgrade Opportunities mechanise (which you may have seen or heard referred to as ADUO) has been put in place as a means of allowing manufacturers to catch up.

In simple terms, if a manufacturer is deemed to have a power unit that is more than 2% adrift of the benchmark at a certain point - post-Miami and two as-yet unconfirmed further dates later in 2026 - then they will be allowed to make one upgrade for 2026 and another for 2027.

If the deficit is 4% or more, then they will be allowed to make two upgrades this season and two more the following campaign.

The possibility for those manufacturers on the backfoot to be able to make in-season improvements opens up the possibility of a change of order, especially with power units being so critical to performance right now.

There has been a lot of talk about the likelihood of who stands to gain and lose from things, especially with Ferrari having been open in expressing it expects to qualify for upgrades and that it sees this as a good chance to slash the advantage that Mercedes has.

Speaking at the Chinese Grand Prix in mid-March, Ferrari team principal Fred Vasseur said: "The addition of the ADUO will be an opportunity for us to close the gap."

But while Ferrari thinks it will get an allowance, the situation is not as clear-cut as it may appear to be from the outside.

Amid the complexities of the way the system is being implemented, plus a level of deliberate opaqueness about how things will be measured and judged, there are wider nuances - especially because the decisions are not based on overall power unit performance.

What is being looked at?

Only one power unit element comes into play: the internal combustion engine. And this is why it is much more complicated to unpick where each manufacturer stacks up now.

Any advantage a team has from better energy harvesting, deployment, efficiency, or more advanced management of energy (which includes control of the MGU-K or better battery technology) is totally outside the remit of what falls under the qualifying criteria for additional development opportunities.

All the FIA is analysing is the performance of the engine, although the exact metrics of how that is done are not clear as these are not laid out in the regulations.

This lack of detailed explanation for what is being measured, and how it is being done, may not make it easy for everyone to understand what is in play, but that is not an accident.

This is because in the competitive world of F1, the FIA is mindful of teams potentially trying to game the system.

It stands to reason that if the FIA laid out some clear measurement metrics on what its analysis and decisions would be based on, then some manufacturers would try to engineer power units that would score low in these areas to help it look like they were behind and so qualify for upgrades.

This also explains why there is a need to constantly evolve processes of measurement to ensure the governing body stays one step ahead of manufacturers trying to win some allowance.

Unpicking a power advantage

Ferrari has been open that it feels it is behind the benchmark Mercedes power unit, and its works team has only been able to take the fight to Mercedes because its chassis is so good.

There have been suggestions that Ferrari is currently somewhere between 15-30bhp down on Mercedes, with Vasseur telling The Race recently the losses in power are costing it close to one second per lap.

"It's not a secret, and you all have access to data and to the balance between grip-limited and power-limited [sections of the track]," he said.

"Clearly, on power-limited, compared to Mercedes, we are something like eight tenths off and much less in the grip-limited, so you can work out the difference."

With the engine delivering around 400kW of power this year (approximately 540bhp), the differences that the FIA is looking for are not that great.

A 2% margin is approximately 10bhp, while a 4% gap is a little over 21bhp.

Ferrari's verdict seems to fit in with speed trace figures that have been observed of cars in action on track, where Mercedes clearly has a top speed advantage.

But with the FIA decision based on the internal combustion engine alone, so separate from the wider power unit, it will take some detailed technical data from track running and dynos to separate out just what the gaps really are.

Some of the straightline speed differences observed are not only down to engine designs; they are the consequence of strategic choices.

In Japan, for example, there was variability between the different engine manufacturers about where they felt best to burn through energy for top speed gains.

Some including McLaren and Ferrari preferred to do it on the start/finish straight, while Mercedes felt it was better to save it for the run from Spoon to 130R.

Differences on the straights between McLaren and Mercedes also cannot be only down to engine hardware, as specifications supplied to customers have to be identical.

Also, in a rules era where the performance of the chassis and power unit has never been so interlinked, it is wrong to jump to the conclusion that more top speed is purely about having more power.

For example, if a car has more downforce and can go quicker around a corner (as Mercedes does compared to its closest rivals), then it comes onto the following straight quicker - which means less energy is required to get it up to top speed and it can therefore deploy for longer.

There are also other elements that cannot be gleaned just from data when it comes to evaluating engine performance either.

Power output is certainly not the only metric that should be used when it comes to judging engine performance.

In fact, manufacturers and teams can make deliberate design choices that boost the competitiveness of the car but mean that compromises are made on the power front.

Some rivals have cited Ferrari as being the perfect example of a team whose engine performance is not reflective of its full potential.

It has been suggested that its radical exhaust wing, which helps deliver more downforce, has consequences in terms of adding back pressure to the exhaust, which impacts the effort needed to expel hot gases and also raises the internal temperature.

Analysis based on work from others has suggested this could be the detriment of up to 10kW, or around 13bhp.

Ferrari's choice in going for a small turbo, which helps improve the driveability of its power unit and is especially useful for starts, also comes with the downside of not delivering as much peak power as rivals who have bigger turbos.

Plus, the high boost temperatures Ferrari is understood to run at are great for car layout optimisation, but they ultimately penalise the power unit.

In each of these cases, design decisions have been made that are focused on improving the overall performance of the car, even if they come at the cost of ultimate engine power.

So should teams that go down a similar route, of picking car pace over power, be deemed to be behind with their engines and therefore be allowed to develop more?

This is something the FIA needs to decide upon.

Plus, there is also the potential for games to be played by teams that may try to be sneaky and not run their power units at maximum performance early on to try to qualify for additional upgrades.

Then, once an upgrade allowance is unleashed, things are turned up with a new spec for a double boost.

Or what about those that have an advantage, maybe turning things down to not be 2% ahead, so nobody gets the green light to improve?

There are a lot of answers being chased from manufacturers about how the FIA is going to deal with such matters, and what the process will be for avoiding potential pitfalls.

Who is the benchmark?

The current uncertainty about the order that will be determined - and ultimately only the FIA will have the full data of engine measurements - means that until a decision is taken about where manufacturers stack up, none of them can take anything for granted about who gets development time and who doesn't.

The most commonly accepted viewpoint is that Mercedes is well ahead, with everyone else other than Red Bull set to get upgrade opportunities.

But there has been an alternative view put forward, based purely on the engine output, that Mercedes will not be judged as the benchmark; Red Bull will be instead.

Some analysis points to the Red Bull engine's early promise - remember Toto Wolff labelling its deployment the "benchmark" in pre-season testing? - still being there, but hidden because other elements of the package, such as the chassis and battery, are letting it down.

If this left-field theory proves true and it turns out that Red Bull comes out on top because its engine is so strong, then could its advantage even be enough for Mercedes to fall outside of the 2% window and be granted some extra development opportunity?

It's unlikely, but not impossible according to some within the paddock.

And if it does happen, then that would be a blow to Ferrari's hopes of reducing the gap to Mercedes.

While the Red Bull rumour is an intriguing one, it is one that the team itself thinks is not correct - although team principal Laurent Mekies admitted that it is not the work of the moment to properly evaluate the power outputs of all teams.

"It's a difficult business to estimate your power output compared to competitors, especially in the game we are in with the energy deployment," he said.

"But we think Mercedes is clearly ahead. Hence with them being clearly ahead, we expect to be in the group of guys that will get the ADUO."

For now, everyone must wait until the FIA's analysis of power units is completed after Miami, with the results set to take a few weeks to come through.

But with the F1 2026 title outcome potentially resting on the outcome, interest has never been higher in how the performance of each engine stacks up.

And, unlike the battle on the track, this is one fight where manufacturers are hoping they are judged to be behind.