2025/2026 Hybrid Powerunit speculation

[johnnycesup]

From the regulations regarding oxygen content, there is in essence a 20% mass limit on ethanol, and that is if every other component in the fuel is completely free of oxygen.

[TeamKoolGreen]

Audi isn't taking no for an answer with regard to the compression "loophole". If this was settled like the media claims it is , there wouldn't be 2 meetings scheduled.

Make or Break Week on Engines!

​The Race reveals two key FIA meetings (Monday & Thursday) to quash the "compression loophole" row.

Ferrari, Honda & Audi want a new "hot engine" test to see Mercedes/RBPT gains

[bonjon1979]

It seems to me that this is a classic f1 rules paradox. The rule states that the compression ratio must be one thing. But then mandates that it is only measured under certain conditions. Teams say they comply as they past the test, but that doesn’t negate what the overall rule dictates. See flexi-wings, fuel flow etc etc. much arguing here, no right or wrong, bun fight in the paddock technical directive incoming but not applicable until such time that it has no real discernible effect.

[bonjon1979]

It seems to me that this is a classic f1 rules paradox. The rule states that the compression ratio must be one thing. But then mandates that it is only measured under certain conditions. Teams say they comply as they past the test, but that doesn’t negate what the overall rule dictates. See flexi-wings, fuel flow etc etc. much arguing here, no right or wrong, bun fight in the paddock technical directive incoming but not applicable until such time that it has no real discernible effect.

[diffuser]

As I posted in the other thread;

V8 drag race and circle track builders set P-H around .040in (1mm) with steel rods which in practice is near zero Piston to Head clearance at redline (the goal is to run around 0.1mm running clearance). This isn’t out of the realm at all.

For a typical racing US domestic V8 with a 4.25in bore, 64cc chambers, and a 10cc dome, that’s a change from to 12:1 to 13.9:1.

This has been a “thing” for decades in race engine building. No fancy degrees or materials needed and certaintly not an industry secret.

All engines are limited by piston to head clearance. You can’t modify this, at some point, they meet, and it’s expensive. Now depending on the rods being used, it may matter. For example, on an American V8 drag race engine, aluminum rods may require 1.50mm p-h clearance ambient vs the 1mm for steel rods. Both will end up around .1mm near redline if you’re doing it right. Both will measure slightly different geometric compression ratios (aluminum being lower) but the same running compression ratio.

Binotto as an engine guy should know this. People building engines in their garages who struggled through high school even know this. This sounds more like sour grapes than anything.

Thought you might find this interesting...

[Hoffman900]

As I posted in the other thread;

V8 drag race and circle track builders set P-H around .040in (1mm) with steel rods which in practice is near zero Piston to Head clearance at redline (the goal is to run around 0.1mm running clearance). This isn’t out of the realm at all.

For a typical racing US domestic V8 with a 4.25in bore, 64cc chambers, and a 10cc dome, that’s a change from to 12:1 to 13.9:1.

This has been a “thing” for decades in race engine building. No fancy degrees or materials needed and certaintly not an industry secret.

All engines are limited by piston to head clearance. You can’t modify this, at some point, they meet, and it’s expensive. Now depending on the rods being used, it may matter. For example, on an American V8 drag race engine, aluminum rods may require 1.50mm p-h clearance ambient vs the 1mm for steel rods. Both will end up around .1mm near redline if you’re doing it right. Both will measure slightly different geometric compression ratios (aluminum being lower) but the same running compression ratio.

Binotto as an engine guy should know this. People building engines in their garages who struggled through high school even know this. This sounds more like sour grapes than anything.

Thought you might find this interesting...

https://youtu.be/hLzto55W3RU?si=Bu9_J7zOVmZDJMLX

It largely said what I have said over a few posts, just with a lot more words.

Interesting he brings up “dynamic compression” which basically calculates compression ratio starting at the crank angle at intake valve closing (IVC). This thought comes from the 2 stroke world where they don’t have valves and the engine can’t begin compressing the mixture until the piston closes off the ports. On a 4 stroke it’s a little bit misleading as once the engine is “on song”, cylinder pressure is above 1 atmosphere before intake valve closing (IVC) as the inertia of air against a rapidly closing intake valve raises port pressure, so compression is occuring to a small amount prior to IVC.

A certain and controversial performance authorhas coined “effective compression ratio” as “dynamic” and has tried to correlate to octane needs for a given combination. This is wrong as octane needs are driven by lots of things like peak firing cylinder pressure, turbulent kinetic energy (TKE), plug position, atomization (and its effect on the mixture temp in the cylinder), etc.

There is nothing dynamic about “dynamic compression ratio”.

Further complicating things is on a Miller Cycle engine, which F1 engines and some of the diesel LeMans engines before 2014 were, closes the intake valve before BDC on the intake stroke. This means the engine has a higher expansion ratio than compression ratio, which in turn lowers cylinder temperatures. This was used by Mazda and Subaru in the early 90s, still used in locomotive engines. It requires big boost / high air flow from the turbo or supercharger to make up for lack of open time of the intake valve. Pat does a great job describing it here starting at 13:00 https://youtu.be/mUq-K9jcaB8?si=06uO7-077SuZjlix . As he points out, by closing the intake valve so early you do lose some of the effect of a longer intake period adding in cylinder motion in the cylinder (typically tumble on a 4 valve head), or when you factor in a few more things, TKE. So that’s why thints like turbulent jet ignition (TJI) are sought out. Honda has a good white paper published this past September about developing TJI systems for large bore sport bike engines, why you want it (the jets increase TKE and create a larger flame surface area, thus reducing knock, and allowing for a higher geometric compression ratio for a given octane), but they also point out it struggles at part throttle operation and is part why you haven’t seen it widely adopted on the street, but I digress…


The Wikipedia and subsequently the AI searches that have trained on the wiki part are wrong about the Miller Cycle. Overall, as he brings it up in the video, the dynamic compression ratio isn’t entirely well explained and it just felt like he was dropping it in there to sound smarter, and also has no idea what it means.

[Tommy Cookers]

the biggest nonsense talked in the 2026 (or 2014) F1 context is 'octane'
(anyway there is no such thing)

RON is a 600 rpm test
MON is a 900 rpm test
(not 10500 rpm or 12000 rpm or 15000 rpm etc)
the biggest factor is TIME

F1 permitted sensitivity is 15
ie F1 fuel can have a RON of 102 and a MON of 87
but 'octane' tests RON and MON are made with reference fuel that tests at 100 RON and 100 MON (what a surprise !)

2014 fuel rules were about avoiding dieselisation
what are 2026 rules about ?

[Hoffman900]

2014 was a failure from that standpoint because they all moved towards “rapid combustion” concepts, ie: self ignition, supplemented with TJI

[FW17]

Furthermore, there is no scope in the regulations to simply run a quick outlap on the internal combustion engine alone, as there are strict rules regarding power demand.

Article 5.12.1 of the Technical Regulations states: “At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”

This effectively means that the trigger for kicking in battery usage is throttle position - not a button on the wheel.

[venkyhere]

Furthermore, there is no scope in the regulations to simply run a quick outlap on the internal combustion engine alone, as there are strict rules regarding power demand.

Article 5.12.1 of the Technical Regulations states: “At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”

This effectively means that the trigger for kicking in battery usage is throttle position - not a button on the wheel.

"Monotonically increasing" means :
d(T-demand)/d(pedal.pos) is a +ve number for all values of pedal.pos, however small or big.
"Linear" is only one of the possible ways.



For example, the green curve can be used for a 'cool' lap, where the driver doesn't press pedal beyond 50% at any stage ; from 25% to 50% "almost all" of the ICE output is used to recharge battery via MGU-K, from 0% to 25%, "almost nil" of the battery output is deployed, and the car can be ready for a Q-lap at the end of the outlap, when they are doing a push-cool-push. In this case, for the 'cool' lap, the ICE is providing 'almost all' the power and the battery gets fully recharged from 25%-50% pedal stage AND from the braking/lift-off recharges.

[FittingMechanics]

Furthermore, there is no scope in the regulations to simply run a quick outlap on the internal combustion engine alone, as there are strict rules regarding power demand.

Article 5.12.1 of the Technical Regulations states: “At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”

This effectively means that the trigger for kicking in battery usage is throttle position - not a button on the wheel.

I think that this is intended to avoid any possibility of making "traction control". They are worried about that. My understanding is that drivers will be able to change the deployment maps and deploy manually.

[Hoffman900]

Furthermore, there is no scope in the regulations to simply run a quick outlap on the internal combustion engine alone, as there are strict rules regarding power demand.

Article 5.12.1 of the Technical Regulations states: “At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”

This effectively means that the trigger for kicking in battery usage is throttle position - not a button on the wheel.

"Monotonically increasing" means :
d(T-demand)/d(pedal.pos) is a +ve number for all values of pedal.pos, however small or big.
"Linear" is only one of the possible ways.

https://i.ibb.co/5gP1JspG/pedal-map-possibilities.png

For example, the green curve can be used for a 'cool' lap, where the driver doesn't press pedal beyond 50% at any stage ; from 25% to 50% "almost all" of the ICE output is used to recharge battery via MGU-K, from 0% to 25%, "almost nil" of the battery output is deployed, and the car can be ready for a Q-lap at the end of the outlap, when they are doing a push-cool-push. In this case, for the 'cool' lap, the ICE is providing 'almost all' the power and the battery gets fully recharged from 25%-50% pedal stage AND from the braking/lift-off recharges.

This holds true for even mechanical linkages. We have used throttle linkages that can vary progression vs pedal position and you can tune this around a driver. Obviously it’s fixed once out the pits, but it’s a tuneable feature.


Dawntreader on X had some cool graphs of old Indy Car throttle progression vs pedal position. All mechanical. Most throttles aren’t linear, even most carb systems.

[dialtone]

Furthermore, there is no scope in the regulations to simply run a quick outlap on the internal combustion engine alone, as there are strict rules regarding power demand.

Article 5.12.1 of the Technical Regulations states: “At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”

This effectively means that the trigger for kicking in battery usage is throttle position - not a button on the wheel.

I think that this is intended to avoid any possibility of making "traction control". They are worried about that. My understanding is that drivers will be able to change the deployment maps and deploy manually.

That’s precisely it. They want the driver to control the throttle and not have them be just pressing and leaving a computer choose the optimal torque.

[Tommy Cookers]

....“At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”....

I think that this is intended to avoid any possibility of making "traction control". They are worried about that. My understanding is that drivers will be able to change the deployment maps and deploy manually.

I think 'monotonic' is more to do with preventing the accelerator helping the driver hover in one part of the envelope
there is (or was) another rule mandating the level of PU torque 'turn-down' rpm-rising accelerator-fixed
(in principle analogous to the FBW-style ICE turn-down since c.2004)

these rules only cover the steady-state or slowly-changing characteristic

dynamically MGU-K 'control' must have TC and ABS-like effects (otherwise it is an unstable or divergent system)
as does the electric vehicle
there's no rules pertaining to this

the so-called control electronics CEs are in effect half of the MGU-K machine
transacting with the machine on a microsecond basis (logging every MGU-K revolution and continuously processing)
over the so-called '3-phase' leads between the CE and MGU-K

the FIA has closed eyes to this

[venkyhere]

....“At any given engine speed, the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.”....

I think that this is intended to avoid any possibility of making "traction control". They are worried about that. My understanding is that drivers will be able to change the deployment maps and deploy manually.

I think 'monotonic' is more to do with preventing the accelerator helping the driver to hover in one part of the envelope
not with 'driver aid' effects ie poor man's TC and ABS

but the rules only cover the steady-state or slowly-changing characteristic

dynamically the MGU-K 'control' must have TC and ABS-like effects (otherwise it is an unstable or divergent system)
like the electric vehicle
there's no rules pertaining to dynamic behaviours

the so-called control electronics

IN PROGRESS .....

You beat me to it..
TC and ABS were already 'woven in' in the KERS era, even before MGU-H/MGU-K came into the picture. Ultimately what is TC and ABS ? some way to 'manipulate' how much of the driver-input goes to the diff or the brake pads, via a man-in-the-middle computer.