2026 Drama: Alleged engine loophole

[Hoffman900]

Except heating the oil and water doesn’t mimic the heat in a running engine, nor does it mimic rod stretch. The piston, chamber walls, etc are MUCH hotter than whatever you’d heat oil and coolant up to.

For the millionth time, piston to head gaps closing up in a running engine 1-1.5mm is completely normal. That can be 1-2pts+ of compression depending on other geometry. Everyone who builds engines understands this.

Calculate it with piston - head clearance being zero, that’s the only way to do this in a fair manner. No AI or lawyers needed. You can’t make the piston go through the head (I’m sure AI would tell one otherwise. )

We know the bore size, we know the stroke, there is a thesis paper from Ilmor Brixworth that shows a plan view of the head / piston of a very similiar engine that you can easily get dome cc and chamber volume from (I’ve shared it on this forum before with zero replies because no one reads, here it is again: https://morethesis.unimore.it/theses/av ... 19-090328/ ), and you can put it in a calculator. Assume head gasket is zero because they don’t use traditional gaskets, and you can play with clearances to see how the geometric combustion ratio changes. Go from say 1mm clearance to .1mm clearance, and watch it change whole points.

[vorticism]

If this recent chatter is what Nugnes meant by the ‘second combustion chamber’ rumor then he could be vindicated. I’m somewhat disappointed as I was hoping for something other than “sub-chamber connected by small hole,” although maybe relieved as it could mean it’s not related to something I wanted to patent years ago

There was already some precedent over the previous decade of the FIA needing to inspect the GCR of an engine that has a small sub-chamber connected by small holes. What was known as the TJI device. Still we don’t know what the GCR test involves, but if it was already being performed during the 18:1 era it would have presumably been able to inspect the TJI sub-cavity i.e. obscured, minimally connected cavities.

I can speculate a functional benefit of such a chamber in so far as it providing a shock absorbing feature in the event of otherwise destructive pressure spikes. Since the orifice would be too small to convey charge air without latency, it would always be lagging behind the main chamber in terms of air pressure. Thus it is lower pressure than the main chamber at TDC and can absorb pressure spikes from knock/detonation, and the passage diameter could be tuned accordiingly. The outflow would conversely display latency, with the sub-chamber retaining higher pressure for longer during the expansion stroke.

Yes TE could still be involved and maybe the hole(s) close totally, but I don’t think it would be necessary to fulfill all the tenets of the rumor.

[Y-250.A]

I just have a weird question , why all the reports about HOT test and new test environment and allegedly a change in the rules came from italian media ? do you guys think FIA and FOM will change the rule ahead of the first GP ? and lets assume they find MB engines illegal , what do they do ? DSQ all the 4 teams ? I don't see it as a possible scenario TBH

[.poz]

Since the orifice would be too small to convey charge air without latency, it would always be lagging behind the main chamber in terms of air pressure.

if the orifice is designed to work as a choke valve once the flux goes supersonic in the narrowest part of the venturi the flux remain constant even if the pressure delta increase

[WardenOfTheNorth]

I just have a weird question , why all the reports about HOT test and new test environment and allegedly a change in the rules came from italian media ? do you guys think FIA and FOM will change the rule ahead of the first GP ? and lets assume they find MB engines illegal , what do they do ? DSQ all the 4 teams ? I don't see it as a possible scenario TBH

Take them all with a mountain of salt.

Firstly, as others have pointed out, taking precise measurements of the geometry of an ICE at full operating temperature is problematic.

[pantherxxx]

I just have a weird question , why all the reports about HOT test and new test environment and allegedly a change in the rules came from italian media ? do you guys think FIA and FOM will change the rule ahead of the first GP ? and lets assume they find MB engines illegal , what do they do ? DSQ all the 4 teams ? I don't see it as a possible scenario TBH

Except they don't have to change a rule. Anything above 16 is already restricted. Only have to change the measurement method.

[.poz]

Based on circulating rumors, three distinct scenarios can be envisioned:

• Scenario 1: The variation in the compression ratio occurs exclusively due to thermal expansion. In my view, this is entirely legal, as the compression ratio fluctuates in every internal combustion engine (ICE) during operation.
• Scenario 2: There is a secondary chamber featuring a duct that is sealed once the engine reaches operating temperature. In my opinion, this is illegal; the sole purpose of such a chamber is to pass the cold-start test. More importantly, sealing the duct triggers a variation in the geometric compression ratio, which is conceptually similar to increasing fuel flow when the sensor is not active (or "off-cycle").
• Scenario 3: A secondary chamber exists with a narrow, unsealed duct. Given that at 15,000 RPM the compression stroke occurs in 1/500 of a second, the pressure does not have sufficient time to equalize between the cylinder and the secondary chamber. This effectively increases the compression ratio without altering the geometric compression ratio. In this case, I wish the legal teams the best of luck: while the secondary chamber’s sole function is to circumvent the test, the geometric compression ratio—which is the only parameter explicitly addressed by the regulations—remains unchanged.

[Luscion]

The FIA have addressed the compression ratio stuff

[bluechris]

The FIA have addressed the compression ratio stuff

In the end it says it all for me.

[Badger]

Nothing very revealing but I must admit that some of the points Tombazis put forward sounded more in favour of a conservative interpretation of the rule.

1. Saying engines were not exceeding 18:1 before, more cons than pros at higher levels.

2. Saying they lowered it to 16:1 to reduce the advantage of established manufacturers, wanting to attract/retain manufacturers.

3. Saying they don't want the sport to turn into rules interpretation.

[LM10]

Nothing very revealing but I must admit that some of the points put forward sounded more in favour of a conservative interpretation of the rule.

1. Saying engines were not exceeding 18:1 before, more cons than pros at higher levels.

2. Saying they lowered it to 16:1 to reduce the advantage of established manufacturers, wanting to attract/retain manufacturers.

3. Saying they don't want the sport to turn into rules interpretation.

He summed up what I was trying to say all the time. There will be people interpreting the rules their way, but it might be different from the intention of the FIA - which was to have a level-playing field, reducing cost and simplifying things for newcomers instead of doing the opposite.

[dialtone]

Very critical they say that you could hardly reach 18:1 level.

So seems like case shut to me, you can’t cross 16:1.

[FNTC]

Kudos to the FIA for talking fairly openly about it at least. The ending statement from Tombazis makes it seem like Mecedes will have to do something at some point. The talk about that this should not be about having "smarter rule interpreters".

[Schumix]

Very critical they say that you could hardly reach 18:1 level.

So seems like case shut to me, you can’t cross 16:1.

Personally, I don't understand this claim that it's difficult to achieve a compression ratio significantly higher than 16:1. Why? Simply because at least three engine manufacturers competing in the 2026 F1 championship say the opposite. It's as simple as that. Let's remember the Ferrari case in 2019: it was Ferrari who told the FIA ​​how their engine exploited the loophole in the fuel flow, and Ferrari explained to the FIA ​​how to eliminate this loophole. F1 engine manufacturers know their engines and the loopholes in the FIA's technical regulations better than anyone else. Secondly, if it's unlikely that an engine manufacturer could achieve a compression ratio higher than 16:1, why not conduct tests as required by the other competitors and quickly put an end to this issue, which risks ruining the competition?

[FittingMechanics]

Nothing very revealing but I must admit that some of the points Tombazis put forward sounded more in favour of a conservative interpretation of the rule.

1. Saying engines were not exceeding 18:1 before, more cons than pros at higher levels.

2. Saying they lowered it to 16:1 to reduce the advantage of established manufacturers, wanting to attract/retain manufacturers.

3. Saying they don't want the sport to turn into rules interpretation.

In regards to point 2, they achieved this. The idea behind going to 16.0 was to force existing manufacturers to have to develop new parts as well. Mercedes obviously did this so the intention of the change was fulfilled.

Any new manufacturer could have easily exploited the same "loophole".

I think the fact they put in writing that the test is at ambient means they will look favorably to teams protesting.