2026 Drama: Alleged engine loophole

[LM10]

It would be highly amusing if we get to September, Merc teams are still rotating engines from the first half of the season into their cars, with no discernible change in engine performance, and another engine manufacturer can no longer use pre-August engines!

Mid-season rule changes rarely work out the way the mob expects. Be that the anti-McLaren/Mercedes mob and flexiwings in 2025, or the anti-RB mob with the early GE era changes around ride-height and plank. Typically, there's no change to the leading cars, and some unexpected side-effects for the struggling teams that make them struggle even more!

I guess we'll see come the September races after the summer shutdown.

Yea... because all the other manufacturers are dumb enough to push for this change - which they did - despite having a PU which would not pass the test. Right?

[zibby43]

It would be highly amusing if we get to September, Merc teams are still rotating engines from the first half of the season into their cars, with no discernible change in engine performance, and another engine manufacturer can no longer use pre-August engines!

Mid-season rule changes rarely work out the way the mob expects. Be that the anti-McLaren/Mercedes mob and flexiwings in 2025, or the anti-RB mob with the early GE era changes around ride-height and plank. Typically, there's no change to the leading cars, and some unexpected side-effects for the struggling teams that make them struggle even more!

I guess we'll see come the September races after the summer shutdown.

Yea... because all the other manufacturers are dumb enough to push for this change - which they did - despite having a PU which would not pass the test. Right?

Not dumb - just paranoid. No different than all the strange theories they cooked up regarding how McLaren generated their rear tire management last year.

[LM10]

FIA giving Mercedes enough time with their illegal engine. Why wait until August to change the measurement procedure if you’re planning to do it anyway?

13 races to build a gap and walk away in the title race.

But I’m not surprised even in the slightest.

Maybe because FIA initially declared the engine LEGAL? Meaning they are partially to blame?

Oh, really?

So Toto went to the FIA - holding a cup of Espresso in his hands - and said "Hey... *sip* so as you know our track record without a significant PU advantage is not THAT good... *sip* what if I told you that we've thought of something extremely clever and built our engine specifically in a way to have a CR of 16:1 at ambient temperature, but shooting up to 18:1 as soon as it gets hot like my Espresso? *sip* I know it was not your intention with this rule, but will you be OK with that?" *sip*

And the FIA said YES? This makes sense!

[bauc]

FIA giving Mercedes enough time with their illegal engine. Why wait until August to change the measurement procedure if you’re planning to do it anyway?

13 races to build a gap and walk away in the title race.

But I’m not surprised even in the slightest.

Maybe because FIA initially declared the engine LEGAL? Meaning they are partially to blame?

Oh, really?

So Toto went to the FIA - holding a cup of Espresso in his hands - and said "Hey... *sip* so as you know our track record without a significant PU advantage is not THAT good... *sip* what if I told you that we've thought of something extremely clever and built our engine specifically in a way to have a CR of 16:1 at ambient temperature, but shooting up to 18:1 as soon as it gets hot like my Espresso? *sip* I know it was not your intention with this rule, but will you be OK with that?" *sip*

And the FIA said YES? This makes sense!

LOL,

https://uz.kursiv.media/en/2025-12-25/f ... 026-rules/

FIA back in December gave the all clear, after in October adding the wording in the rules ''at ambient temp''
Mercedes said it had communicated with FIA all along through this development so yes, they were aware,

Grow up man.

[AnotherAlex]

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.

Wouldn't the +x / -x part of (16+x)/(1-x) = 18 only apply if the dimension changing was the distance of the crank pins from the centre of rotation of the crankshaft?
(I wish Red Bull would share a little more of their understanding of how Mercedes were planning to work around the compression ratio limit. )

[dialtone]

14 cars instead of 22 isn't good reasoning. As Vasseur said, it's a lot easier to reduce compression than increase it, and the Brabham fan car is only the most famous precedent for giving no time to replace a car that was deemed illegal after one race.

If you make mockery of the rules like this as a governing body you will soon have a circus going on.

[Arcanum]

It would be highly amusing if we get to September, Merc teams are still rotating engines from the first half of the season into their cars, with no discernible change in engine performance, and another engine manufacturer can no longer use pre-August engines!

Mid-season rule changes rarely work out the way the mob expects. Be that the anti-McLaren/Mercedes mob and flexiwings in 2025, or the anti-RB mob with the early GE era changes around ride-height and plank. Typically, there's no change to the leading cars, and some unexpected side-effects for the struggling teams that make them struggle even more!

I guess we'll see come the September races after the summer shutdown.

Yea... because all the other manufacturers are dumb enough to push for this change - which they did - despite having a PU which would not pass the test. Right?

More like the old proverb, "Be careful what you wish for, as you just might get it". Maybe all the other engine manufacturers are not on board with the new rule? Maybe Merc's quite happy with it because they know they pass?

As nearly every thing in this thread is based on rumors, who knows?

My theory, which is perhaps no better than anyone else's, is that this is far more boring that people would like to think. Like most engine builders, Mercedes would know that under peak operating conditions of temperature and RPM, the CR is going to be higher than at ambient. So they likely thought, "what are we optimising for?". Are we optimising for CR being 16:1 at all times? Most here would say "yes" (though might change their view if it was Ferrari or RBPT). But, OK, how about those rigid & immovable aerodynamic surfaces codefied in the rules? No one builds wings that are rigid and immovable! So any good engineer would be figuring out when does the engine really have to meet a 16:1 CR. Because if it really is, "at all times", then that's leaving a lot of margin on the table that *surely* other engine manufacturers will exploit. Hence the request for clarity on how the rule is measured.

The fact that the new rule is measured at 130C, and not something even more stringent suggests that other engine manufacturers aren't achieving 16:1 at all times either. Many on this thread seem convinced it's possible to measure 16:1 under peak operating conditions, so why haven't other teams pushed for this? Maybe not possible? Maybe others cannot meet 16:1 either. ::shock:: they are all cheating!

The 130C rule likely covers off anyone finding some egregious violation of the rule, while avoiding a situation where others/many/all of them would be found to exceed 16:1.

[venkyhere]

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.

Wouldn't the +x / -x part of (16+x)/(1-x) = 18 only apply if the dimension changing was the distance of the crank pins from the centre of rotation of the crankshaft?

Yes of course. It's crude back of the envelope calculation, doesn't account for expansion of the bottom of the head, bore expansion etc. Just chose the 'biggest candidate' (the rod) to show that it doesn't take much for the GCR to increase from 16 to 18.

[Arcanum]

(I wish Red Bull would share a little more of their understanding of how Mercedes were planning to work around the compression ratio limit. )

They likely don't know. Just like all the ideas being thrown around last year about how McLaren kept their rear tires cool. They were just throwing ideas around, hoping one of them stuck.

If there really was an ex-Mercedes engineer who had told a competitor what they were doing, and especially if it was something obviously illegal, it would have been leaked to the press. If teams didn't trust the FIA and felt they were colluding with Mercedes, and knew what was going on, it would come out.

As I wrote above, I think this is all far more mundane, with Merc wanting to know what they were optimising for, and therefore asked for clarification on the test conditions for the rule. Which was given as ambient in October.

Since the 130C rule has been proposed, Laurent Mekkies said:
“We don't really mind if the regs goes left or if the regs goes right,” he said. “What we absolutely want is clarity on what we can do and what we cannot do, "That's what we are working with the FIA and the other power unit manufacturers to have this absolute clarity. I'm confident that we will reach that point.”

And Fred Vasseur said:
"We are there to have a clear regulation and to have everybody with the same understanding of the regulations."

In other words, they will be optimising CR to this updated measurement too!

[vorticism]

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?

[bluechris]

As i said since the beginning of this, DarthToto rules

[upsidedowntoast]

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.

[Piston Pin]

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?

[venkyhere]

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?

law of diminishing returns :
how much more can be increased beyond 18:1 until knocking starts to happen ? 19 ? I don't think so. Probably some 18.5 (max). That's nothing like going from 16 to 18, which can be easily accommodated knock-free, since they have already done 18 previously.

[f1isgood]

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?

“5.4.6 No cylinder of the engine may have a geometric compression ratio higher than 18.0.”

Source: https://www.fia.com/sites/default/files ... -04-07.pdf

That's all it states in last year's regulations. That the FIA modified it in October for 2026 is very funny.

For 2026 (the 2023 and 2024 editions state)

No cylinder of the engine may have a geometric compression ratio higher than 16.0. The
procedure which will be used to determine this value may be found in the Appendix to the
Technical and Sporting Regulations.

Source: https://www.fia.com/sites/default/files ... -06-20.pdf (June 2023)


It's interesting that they added an extra line compared to the previous regulations. Almost like they wanted someone to exploit the loophole?