2026 Drama: Alleged engine loophole

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CrazyCarperF1
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Re: 2026 Drama: Alleged engine loophole

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It will be interesting to see what tolerance the fia uses for measurement, what +/- variance from 16:1 is given for the inaccuracies of the tests. Surely whatever temperature value is selected for test is arbitrary 130c is still meaningless unless this is the upper running temperature for all engines,

Piston Pin
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Re: 2026 Drama: Alleged engine loophole

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How do you measure in warm engine condition? At the moment it is not clear if warm engine means static engine at running condition temperature or running engine. If we have running engine, is it at specific operating point (rated or motoring)? CR is not only affected by temperature it is also matter of elastic cranktrain deformation under the combustion load and inertia of the parts.
One thing comes to my mind, compression ratio could be calculated on basis of measured pressure during compression stroke. Question is how reliable these measurements are.
Anyhow, very interesting topic we have here.

Andi76
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Re: 2026 Drama: Alleged engine loophole

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venkyhere wrote:
18 Feb 2026, 17:04
Andi76 wrote:
18 Feb 2026, 15:08
In addition, the strict prohibition of variable geometry systems under Article C5.7 applies here. If an engine increases its compression ratio from 16:1 to 18:1 solely through material expansion, thermal physics effectively acts as a dynamic actuator. Such a change in combustion characteristics of more than 12% is no longer a negligible tolerance, but a functional geometry change that aims to circumvent the static limits of the homologation dossier.
Sorry for being pedantic, the 16:1 changing to 18:1 isn't a 12% change in dimensions of something.
(16+x)/(1-x) = 18.
Solving, we get x=(2/19)=0.105
which works out to (0.105/16)*100 = 0.656%

If we are talking about conrod+piston that is in contact with something upwards of 2000+ celcius, I think 0.6% is not out of the ballpark of 'tolerance'.
Of course the regulations would have restricted the usage of metals for the rod/piston/gudgeonpin/bearing inserts etc etc to disallow as much expansion as possible ; and we have theories ranging from 'exotic 3D printing' to 'some speciall milling technique' to enable unequal expansions to the full-hollywood 'secret chamber' going around to explain the 16:1 rising to 18:1. That said, the reason I posted is to highlight 'how little' of change in dimension is needed to increase the compression ratio , it's not a giant number like 12%, more like 1/20th of that.
While that’s an interesting take, it unfortunately relies on a fundamental misunderstanding of how compression ratio (CR) is defined and how engine tolerances actually work.
​1. The Mathematical Error:
Your equation \frac{16+x}{1-x} = 18 doesn't actually represent the physical volume change in a cylinder. The compression ratio is defined as CR = \frac{V_s + V_c}{V_c} (where V_s is swept volume and V_c is clearance volume). To move from a 16:1 ratio to 18:1, the clearance volume (V_c) would need to shrink from 1 unit to roughly 0.882 units. That is a 11.8% reduction in combustion chamber volume—not 0.6\%. Your math significantly underestimates the physical change required.
​2. Mechanical Reality vs. 'Tolerance':
Even if we look at your 0.6\% figure, in high-end motorsport like F1, that is an astronomical distance. On a 100 mm connecting rod, 0.6\% is 0.6 mm. Engine builders obsess over 'Piston-to-Head Clearance' (squish) measured in fractions of a millimeter. An unplanned expansion of 0.6 mm would cause the piston to mechanically strike the cylinder head at high RPM, resulting in immediate engine failure. It’s not 'within the ballpark of tolerance'; it’s a catastrophic collision.
​3. Thermal Expansion:
While combustion gases reach 2000^\circ C, the physical components (pistons and rods) are aggressively cooled by oil jets and water jackets to stay within a specific thermal window (usually under 300^\circ C for the piston crown). If a material expanded enough to passively alter the compression ratio by two full points, it would likely lose its structural integrity and 'melt' or seize long before reaching that state.
​Conclusion:
The jump from 16:1 to 18:1 (often discussed regarding Mercedes’ HPP gains) isn't achieved by parts physically growing; it’s achieved through Turbulent Jet Ignition (TJI) and pre-chamber technology that allows the engine to run incredibly lean mixtures without knocking. It’s a victory of chemistry and fluid dynamics, not 'Hollywood' thermal expansion.

Andi76
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Re: 2026 Drama: Alleged engine loophole

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zibby43 wrote:
18 Feb 2026, 15:30
Andi76 wrote:
18 Feb 2026, 15:08
I haven't read or followed the current state of the discussions here, but I would still like to say a few words about it, because I find the topic problematic in many ways. First of all, because an engine that has a compression ratio of 18 instead of 16-1 when warm, regardless of the reason and solution, is undoubtedly illegal.
The current debate about the 2026 Mercedes engine and its alleged dependence on thermal conditions for compliance (or exceeding) compression limits raises fundamental questions for me about the integrity of the technical regulations. A design that has a compression ratio of 16:1 when cold but rises to 18:1 when warm is, according to the wording of the FIA regulations for 2026, undoubtedly illegal.
The most important anchor point for this argument can be found in Article C1.5, which establishes the principle of "continuous conformity." A Formula 1 car must comply with the rules "at all times during a competition in their entirety." This clause leaves no room for an engine that only expands into a more powerful but illegal state when heated up during operation. Since technical inspection (scrutineering) and physical inspection of the hardware are usually carried out in a static state in accordance with Article C1.7, the hardware must already comply with the specifications beyond any doubt at this stage. "Growing" into a different geometry due to heat negates controllability and breaks with the principle that the car must be legal at every moment of the race weekend.
In addition, the strict prohibition of variable geometry systems under Article C5.7 applies here. If an engine increases its compression ratio from 16:1 to 18:1 solely through material expansion, thermal physics effectively acts as a dynamic actuator. Such a change in combustion characteristics of more than 12% is no longer a negligible tolerance, but a functional geometry change that aims to circumvent the static limits of the homologation dossier.

What makes the whole thing even more serious is that it is basically the same thing that Ferrari did in 2019, which is now clearly branded as cheating and was also judged as such. While Ferrari used the time component at the time to inject more fuel than allowed between the measurement intervals of the fuel flow sensor, this concept now uses the temperature component. In both cases, a dynamic state (oscillation frequency at Ferrari, thermal expansion at Mercedes) is abused to render a static measurement by the FIA worthless. The aim is to decouple the physical reality on the race track from the measurable reality in the pit lane.
In conclusion, it should be noted that, according to Article C1.6, the FIA expressly has the right to prohibit technologies that serve solely to undermine the intention of the regulations. An engine whose compression ratio deviates so massively from the base values during operation undermines the level playing field and the technical monitorability of the sport. Mercedes' argument that such an interpretation has been approved by the FIA directly contradicts the requirement for hardware conformity "at all times." Anyone who uses physics to dynamically shift the hardware limits of the regulations is not practicing engineering in the spirit of the sport, but rather systematically circumventing the rules. That said, we must come back to Ferrari here as well—Ferrari also had "the FIA's assurances" at the time, as Binotto said.

So if the Mercedes engine is classified as legal today, if it really does what is rumored, then in my opinion the FIA would make itself completely untrustworthy and incompetent. Because you can't say today that it's legal for Mercedes to abuse a dynamic state to circumvent a measurement when yesterday it was illegal for Ferrari. That would be a double standard. If it's Ferrari, it's illegal; if it's Mercedes, it's legal. It also exposes the rules to ridicule. Because the rules are so clear on this point that they couldn't be any clearer. Then there's no need for rules anymore if the FIA a) measures with double standards and without any consistency and b) if every scandal is circumvented. Because ultimately, it would be a scandal if such a Mercedes engine were classified as illegal. Mercedes would probably leave F1, (justifiably) branded as cheaters, just like Ferrari in 2019. The 2026 F1 World Championship would probably lose five teams or have to disqualify them, causing a huge outcry worldwide and billions in losses. However, one must also ask oneself: how credible are you if you don't take action? What message are you sending? Why write regulations at all if a team with enough customers can do whatever it wants? Don't the others get fed up at some point with always being the idiots while others get away scot-free?

Sorry, but for me, we have reached a point where you have the choice between exposing yourself to ridicule and being superfluous, or justifying your existence and proving your substance, significance, justice, and necessity. If that doesn't happen, everything is just a farce, because you are clearly saying, "You can do whatever you want." You don't even have to follow clear rules yourself, because we can't do anything about it, we are powerless. We can't classify half the starting field as illegal, the scandal would always be too big, as would the loss of image and money. But the rest of you, even if you are always at a disadvantage as a result, you have to comply with everything, and if you don't, you pay and you get punished.

So if there is any truth to the rumors, in my opinion this is a historic moment for the FIA and its existence, as well as for justice and equal treatment in F1. If I were Ferrari president and Mercedes had done this and gotten away with it, I would a) demand the money back that the "penalty" cost in 2019 and b) leave F1 immediately.
Apply that logic to flexible body work and how all teams used it despite being able to pass static load tests.

Hint: You cannot.
Nice try. A hint - i can. And the comparison to flexible bodywork (aero-elasticity) actually reinforces my logic rather than debunking it. There are three fundamental reasons why Mercedes’ alleged thermal expansion is a different breed of rule-breaking compared to a flexing front wing:
​First, we have to distinguish between unavoidable physics and functional geometry changes. The FIA explicitly acknowledges in Article 3.15 that no material is infinitely stiff. Consequently, they define specific static load tests; as long as a wing passes these tests, it is deemed legal, even if it deflects under high aerodynamic loads. However, we are talking about a compression ratio jump from 16:1 to 18:1. That is a 12.5% deviation in a core engine parameter. If a front wing were to change its angle or surface area by 12.5% during a run, it would fail any load test instantly and be flagged as a "moveable aerodynamic device."
​Second, the "static test" defense for wings exists because there is no other way to measure them in a wind tunnel or on track with 100% precision. But for an engine, the compression ratio is a fixed value in the homologation dossier. If you homologate a power unit at 16:1 but design it to operate at 18:1 the moment it gets hot, you aren't exploiting a "flex" margin; you are submitting a fraudulent technical specification. It is the equivalent of a team building a wing that stays rigid under a 1000N static load but uses a thermal actuator to flatten out at 300 km/h—something the FIA has banned repeatedly (e.g., the flexible floor clampdowns).
​Finally, Article C1.5’s principle of "continuous conformity" is much stricter for internal engine components than for external surfaces. Under Article C5.7, variable geometry systems are strictly prohibited. In this scenario, thermal expansion acts as a dynamic actuator. Using physics to bypass a static measurement is exactly what Ferrari did in 2019 with fuel flow oscillations. Just as the FIA ruled that "intermittent" legality is still "total" illegality, an engine that only exceeds limits when warm is a breach of the rules "at all times."
​To equate a few millimeters of wing-flex with a massive, 2-point shift in compression ratio is to ignore the scale and intent of the regulations. One is an inherent property of carbon fiber under load; the other is a calculated circumvention of the engine’s legal hardware limits. If the cylinder head is designed to "grow" into an illegal state, it’s not engineering—it’s a bypass.

Rodak
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Re: 2026 Drama: Alleged engine loophole

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CrazyCarperF1 wrote:
18 Feb 2026, 18:54
It will be interesting to see what tolerance the fia uses for measurement, what +/- variance from 16:1 is given for the inaccuracies of the tests. Surely whatever temperature value is selected for test is arbitrary 130c is still meaningless unless this is the upper running temperature for all engines,
Probably +0.0, - whatever.

upsidedowntoast
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Re: 2026 Drama: Alleged engine loophole

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Piston Pin wrote:
18 Feb 2026, 18:38
upsidedowntoast wrote:
18 Feb 2026, 18:32
vorticism wrote:
18 Feb 2026, 18:23
The fact that these questions did not arise in 2025 and prior when the limit was 18:1 may suggest that there's nothing to the rumors nor the FIA directives/rule changes. Was it not advantageous to exceed 18:1 in 2025? What did the test entail last year? Was it not tested?
It's very hard to go above 18:1 without your engine shredding itself and running into reliability issues. 18:1 seems to be that sweet spot where anything above is limited gain.

And up until now the test has always been an ambient temperature (20-25C).

Now, regarding this new proposed hot test, they say 130C. Correct me if I'm wrong, but just days ago Merc passed a compression ratio test where they heated the engine to 150C but by the time they took the measurement it had cooled down to 75C. (This is approximately how hot the whole engine gets.)

Meanwhile pistons and cylinders get up to 2600C during operation. So...how exactly does this new proposed test help? Unless the 130C means that they run the whole engine until it gets to 130C, and then they disassemble it while hot and measure the pistons and cylinders (which are actually at a higher temp than the rest of the engine)...but I would assume that the time it takes to disassemble the engine to properly take the measurement would allow it to cool down significantly.

I can't let go of my conspiracy theory that the compression ratio trick is actually a nothingburger smokescreen and it's real something else.
Huh, 2600C, where did you come up with that number mate?
https://www.racecar-engineering.com/tec ... c-cooling/

It's the temp of the gas inside the cylinder not the metal itself, but I would assume that the metal gets way hotter than 130C or whatever.

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Re: 2026 Drama: Alleged engine loophole

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If all cars can pass the test, why wait until August 1st?
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hollus
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Re: 2026 Drama: Alleged engine loophole

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130°C sounds like the maximum temprature that the water cooling systems can handle. There was a max pressure and water would boil abobe 130°C IIRC.
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Re: 2026 Drama: Alleged engine loophole

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Badger wrote:
18 Feb 2026, 15:41
Temp for the new test is 130 degrees C. To be voted on.
I’ll not be volunteering to check them!!
How does paraffin behave when introduced to a hot restricted volume from ambient?

When/where will they be tested?
If tested at mid lifecycle will they be able to be reassembled after testing/verification?

Will a device that fits into the spark plug hole be used (a known volume of fluid would be contained within) which would show the full swept volume and compression chamber volume at operating temperature? This would need to be completed on all six cylinders….

With the bore/stroke being so closely defined they could/should follow @Hoffman900’s rule on combustion chamber compliance (assume zero piston-head clearance).

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Re: 2026 Drama: Alleged engine loophole

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What is an "e-vote" and why is the FIA making a spectacle out of this?
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jacme22
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Re: 2026 Drama: Alleged engine loophole

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Bet: if at least one other engine is as good as the Merc, and there is no dominance from one team, they will walk back on this and discard the new measurement method.

fourmula1
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Re: 2026 Drama: Alleged engine loophole

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jacme22 wrote:
18 Feb 2026, 22:33
Bet: if at least one other engine is as good as the Merc, and there is no dominance from one team, they will walk back on this and discard the new measurement method.
Not necessarily. All the teams agreeing to a new rule clarification and testing procedure helps everyone: FIA perception, team engineers, and fans. Rule clarification and robust tests are fine for everyone. No one knows if this holds any consequence or Merc engines or anything else.

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Re: 2026 Drama: Alleged engine loophole

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hollus wrote:
18 Feb 2026, 19:42
130°C sounds like the maximum temprature that the water cooling systems can handle. There was a max pressure and water would boil abobe 130°C IIRC.
130° sounds like a number engineered for Merc to pass the test lol :D

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AR3-GP
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Re: 2026 Drama: Alleged engine loophole

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What would stop Mercedes from rushing all of the allocation into use before August like they did in 2017 with the oil burning TD?
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Re: 2026 Drama: Alleged engine loophole

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AR3-GP wrote:
18 Feb 2026, 23:18
What would stop Mercedes from rushing all of the allocation into use before August like they did in 2017 with the oil burning TD?
All of the allocation into use?