2025/2026 Hybrid Powerunit speculation

[saviour stivala]

There is so much chatter about 'steel cylinder head' in the media (as well as here) and it has left me wondering :
The engine is the same 1.6L as the previous era yet is now going to produce 500bhp peak, instead of 800bhp peak before, so lower max boost level, lower peak pressures etc etc. So why has 'ICE performance' suddenly become a hot topic ? Or has the fuel flow rate limit been massively reduced, demanding more 'efficiency' ? What am I missing ?

It's because the hybrid rules require every last hp.

In the previous rules, a few hp didn't really change much.

But under the 2026 rules, extra power means more opportunity to recover energy to the battery.

No increase in internal combustion engine horsepower will directly translate to extra harvesting to charge the energy store in formula 1 2026. In fact the new regulations shift the balance of power significantly, decoupling a large portion of energy recovery from the IC's operation. Major key change is the removal of the MGU-H, The most crucial change, which previously recovered energy from the exhaust gases. Meaning a major source of energy recovery tied to engine heat is gone.

[wuzak]

There is so much chatter about 'steel cylinder head' in the media (as well as here) and it has left me wondering :
The engine is the same 1.6L as the previous era yet is now going to produce 500bhp peak, instead of 800bhp peak before, so lower max boost level, lower peak pressures etc etc. So why has 'ICE performance' suddenly become a hot topic ? Or has the fuel flow rate limit been massively reduced, demanding more 'efficiency' ? What am I missing ?

It's because the hybrid rules require every last hp.

In the previous rules, a few hp didn't really change much.

But under the 2026 rules, extra power means more opportunity to recover energy to the battery.

No increase in internal combustion engine horsepower will directly translate to extra harvesting to charge the energy store in formula 1 2026. In fact the new regulations shift the balance of power significantly, decoupling a large portion of energy recovery from the IC's operation. Major key change is the removal of the MGU-H, The most crucial change, which previously recovered energy from the exhaust gases. Meaning a major source of energy recovery tied to engine heat is gone.

Not this again!

It is clear to veryone, except you, that the ICE will burn extra fuel to charge the battery.

The extra power is useful to charge the battery when at part load.

[TimW]

I am not so sure if a slightly higher ICE efficiency will really be decisive. Yes, a few extra kJ in the acceleration phase will mean extra kJs recovered, meaning in the next straight you have extra electrical energy as well. Also it will give more battery charging in the off throttle phases.
BUT better aero efficiency will have exactly the same effect. Less energy lost in acceleration and coasting phases will mean more recovery, less drag in off throttle phases will mean more opportunity to charge the battery.
The same goes for electrical efficiency, and even mechanical grip helps.

[Martin Keene]

The engineering calculus behind Ferrari's Steel choice:

The news of Ferrari experimenting with a steel alloy cylinder head is a masterclass in sophisticated engineering. Far from a step backward, this move can be seen as a precise, strategic calculation where the advantages are decisive and the apparent drawbacks are not obstacles, but simply new parameters for innovation.

The Decisive Advantages:

· Unmatched Durability & Power Density: Steel's inherent strength offers an unprecedented foundation for engine rigidity and longevity. Crucially, this strength allows for a more compact and power-dense design, a critical advantage for packaging and vehicle
dynamics.

· Enhanced Thermal Efficiency: By retaining more combustion heat within the cylinder, steel directly boosts thermodynamic efficiency. This translates to a tangible gain in power and torque, extracting more work from every drop of fuel.

· Strategic Manufacturing Efficiency: The use of steel can streamline production, offering cost and complexity benefits that can be redirected into other areas of advanced engineering.

The Challenges, Recontextualized:
The characteristics often framed as weaknesses are, in this light, not prohibitive, but simply key elements of the design equation—elements Ferrari's engineers are uniquely equipped to solve.

· Weight: While steel is denser, the ability to create a significantly smaller and more compact engine package can lead to a net neutral—or even favorable—impact on overall vehicle weight distribution. The mass is centralized and used structurally.

· Thermal Management: Modern Ferrari engines are masterpieces of thermal management, with advanced, track-proven cooling systems. The "challenge" of heat retention becomes the "opportunity" for precise temperature control, turning a potential drawback into a tunable performance variable.

· Modern Relevance: To label this choice "outdated" is to misunderstand Ferrari's history of rewriting conventions. If any manufacturer can leverage the core benefits of steel while mitigating its traditional downsides through material science and systems engineering, it is Ferrari. This isn't a return to the past; it's a reapplication of a fundamental material with a modern toolkit.

Conclusion:
The narrative isn't about accepting old compromises. It's about Ferrari seeing a clear path where the profound benefits of strength, efficiency, and packaging are paramount, and where their engineering prowess renders the typical disadvantages manageable—or even advantageous. This is not a compromise; it's a calculated pursuit of a specific performance ideal.

From https://x.com/Scuderiascoop/status/2007937763920785860

so that people can confirm or debunk what is written there.

But it doesn't allow for a more compact engine design. The bore size and stroke, which are the most fundamental elements that make up the size of an engine, and limited by the rules. What material the head is made of is meaningless.

The thermal conductivity is not a win either, it does exactly as you said, retains heat in the cylinder, as in the walls and flame face of the cylinder head, it doesn't suddenly mean that heat energy gets used as mechanical energy to drive the crankshaft. In fact with steel being ~1/5 as conductive as aluminum, most of that heat is going to be retained in the cylinder head rather than being transferred to the coolant. Now, that might be good from an aero perspective, smaller radiators, I wouldn't fancy the chances of 4 engines doing an complete season before they crack due to high cycle fatigue due to heat.

[Martin Keene]

The engineering calculus behind Ferrari's Steel choice:

The news of Ferrari experimenting with a steel alloy cylinder head is a masterclass in sophisticated engineering. Far from a step backward, this move can be seen as a precise, strategic calculation where the advantages are decisive and the apparent drawbacks are not obstacles, but simply new parameters for innovation.

The Decisive Advantages:

· Unmatched Durability & Power Density: Steel's inherent strength offers an unprecedented foundation for engine rigidity and longevity. Crucially, this strength allows for a more compact and power-dense design, a critical advantage for packaging and vehicle
dynamics.

· Enhanced Thermal Efficiency: By retaining more combustion heat within the cylinder, steel directly boosts thermodynamic efficiency. This translates to a tangible gain in power and torque, extracting more work from every drop of fuel.

· Strategic Manufacturing Efficiency: The use of steel can streamline production, offering cost and complexity benefits that can be redirected into other areas of advanced engineering.

The Challenges, Recontextualized:
The characteristics often framed as weaknesses are, in this light, not prohibitive, but simply key elements of the design equation—elements Ferrari's engineers are uniquely equipped to solve.

· Weight: While steel is denser, the ability to create a significantly smaller and more compact engine package can lead to a net neutral—or even favorable—impact on overall vehicle weight distribution. The mass is centralized and used structurally.

· Thermal Management: Modern Ferrari engines are masterpieces of thermal management, with advanced, track-proven cooling systems. The "challenge" of heat retention becomes the "opportunity" for precise temperature control, turning a potential drawback into a tunable performance variable.

· Modern Relevance: To label this choice "outdated" is to misunderstand Ferrari's history of rewriting conventions. If any manufacturer can leverage the core benefits of steel while mitigating its traditional downsides through material science and systems engineering, it is Ferrari. This isn't a return to the past; it's a reapplication of a fundamental material with a modern toolkit.

Conclusion:
The narrative isn't about accepting old compromises. It's about Ferrari seeing a clear path where the profound benefits of strength, efficiency, and packaging are paramount, and where their engineering prowess renders the typical disadvantages manageable—or even advantageous. This is not a compromise; it's a calculated pursuit of a specific performance ideal.

From https://x.com/Scuderiascoop/status/2007937763920785860

so that people can confirm or debunk what is written there.

But it doesn't allow for a more compact engine design. The bore size and stroke, which are the most fundamental elements that make up the size of an engine, and limited by the rules. What material the head is made of is meaningless.

The thermal conductivity is not a win either, it does exactly as you said, retains heat in the cylinder, as in the walls and flame face of the cylinder head, it doesn't suddenly mean that heat energy gets used as mechanical energy to drive the crankshaft. In fact with steel being ~1/5 as conductive as aluminum, most of that heat is going to be retained in the cylinder head rather than being transferred to the coolant. Now, that might be good from an aero perspective, smaller radiators, I wouldn't fancy the chances of 4 engines doing an complete season before they crack due to high cycle fatigue due to heat.

Steel is an alloy that uses iron as an ingredient. That doesn’t make it iron. Especially when ‘cast iron’ these days contains a lot of other elements which means they are technically alloys not cast iron. Which in my book makes the 2% carbon the key point, less than that and it is a steel alloy that is not allowed. Above that it is an iron alloy and it is allowed. Though why anyone would want a CI head in F1 is a mystery.

In the current version of the regulations:

https://www.fia.com/system/files/docume ... 2-10_0.pdf

The relevant section is as follows:

C15.7.8 Static components:
a. Other than Inserts within them, engine crankcases including sump, Cylinder Heads, their
respective covers and cylinder head cam covers must be manufactured from aluminium or
iron-based alloys.

In Part C of the regulations we can find the definition of what a "X Based Alloy" is:

“X Based Alloy”: (e.g., Ni based alloy) – X must be the most abundant element in the alloy on a
%w/w basis. The minimum possible weight percent of the element X must always be greater than
the maximum possible of each of the other individual elements present in the alloy.

So yes, steel is an Iron-based alloy as far as the regulations are concerned. There are even specific steel grades, like AMS 6487 (a low alloy steel with 0.4%Carbon), in the list for allowable iron-based alloys for pistons.

Ah ha, yes, that is the piece of information I was missing, so yes. Steel is allowed according to that rule.

[mzso]

There is so much chatter about 'steel cylinder head' in the media (as well as here) and it has left me wondering :
The engine is the same 1.6L as the previous era yet is now going to produce 500bhp peak, instead of 800bhp peak before, so lower max boost level, lower peak pressures etc etc. So why has 'ICE performance' suddenly become a hot topic ? Or has the fuel flow rate limit been massively reduced, demanding more 'efficiency' ? What am I missing ?

Yes, and also what wuzak said. (Also you can ingnore "saviour")

From:
100 kg/h ≈ 4,300 MJ/h
to:
70–72 kg/h (fuel-dependent) ≈ 3,000 MJ/h

Ah ha, yes, that is the piece of information I was missing, so yes. Steel is allowed according to that rule.

Also by the meanings of the words steel and iron alloy.

[Martin Keene]

Ah ha, yes, that is the piece of information I was missing, so yes. Steel is allowed according to that rule.

Also by the meanings of the words steel and iron alloy.

Nope.

Steel is an alloy.
Iron can be both, it can be cast or an alloy. But what most people think of as cast iron, is actually an alloy.

[wuzak]

Ah ha, yes, that is the piece of information I was missing, so yes. Steel is allowed according to that rule.

Also by the meanings of the words steel and iron alloy.

Nope.

Steel is an alloy.
Iron can be both, it can be cast or an alloy. But what most people think of as cast iron, is actually an alloy.

Iron is a periodic element.

"Cast iron" is an alloy.

Pure iron is probably only ever cast when making ingots.

Steel is an alloy where iron is the primary constituent.
Iron-alloy is an alloy where iron is the primary constituent.

[wuzak]

The thermal conductivity is not a win either, it does exactly as you said, retains heat in the cylinder, as in the walls and flame face of the cylinder head, it doesn't suddenly mean that heat energy gets used as mechanical energy to drive the crankshaft. In fact with steel being ~1/5 as conductive as aluminum, most of that heat is going to be retained in the cylinder head rather than being transferred to the coolant. Now, that might be good from an aero perspective, smaller radiators, I wouldn't fancy the chances of 4 engines doing an complete season before they crack due to high cycle fatigue due to heat.

I would think that the extra heat retained in the cylinder will either lead to more mechanical energy to drive the crankshaft (ie more power), or will be expelled through the exhaust. Probably moreso the latter.

And there may be some heat transferred to the coolant, but likely not as much as aluminium alloy.

Heat through the exhaust may benefit the turbo system, but I'm not sure how.

It certainly would have helped with MGUH recovery in the last regulations.

[venkyhere]

Heat through the exhaust may benefit the turbo system, but I'm not sure how.

It certainly would have helped with MGUH recovery in the last regulations.

In exactly the same way that 'hotter' exhaust benefits the MGU-H, it will benefit the turbo as well. Ultimately it's heat energy (and thus the 'speed of expansion') used to turn turbine blades, in both cases, isn't it ? (off throttle -> turn the MGU-H turbine, on-throttle -> turn the compressor turbine). Unless there is some 'clever fine print' that you are implying.

[Badger]

Extra weight in the cylinder head… I’m no engineer but wouldn’t the moving engine parts be the last place you want heavier components? Doesn’t that just zap power?

The cylinder head isn't a moving part.

Yeah I confused it with the piston head:(

If you are not as weight limited on the engine I guess you can invest in a heavier block.

[Hoffman900]

There are two problems with some of these thoughts:

1) while higher heat may help the turbo extract more energy, it’s problematic from an exhaust reliability standpoint. Cooling the exhaust pipe is a tradeoff with what the aero engineers want. We’ve already seen this be a problem with teams.

2) A “steel” head will hold onto more heat. This heat will be transfered to to the mixture in the cylinder raising propensity for knock. These engines are already knock limited due to the fuel flow rules. This is why they are all Miller Cycle (reduces end gas temp due to more expansion) and utilize turbulent jet ignitions (the jets increase turbulent kinetic energy) which raises combustion speed, thus reducing knock. An acquaintance at Ilmor I know refers to these PU’s as “controlled knock” engines. This is why they can’t run without in-situ pressure sensors controlling the the whole process.

Some reading as it applies to F1 engines that may be helpful to you guys. These get into controlling knock, and another brings up EGT’s (exhaust gas temp) in relation to energy extraction:

All co-authored with Ferrari and open source to download:

Model-Based Pre-Ignition Diagnostics in a Race Car Application

https://www.mdpi.com/1996-1073/12/12/2277

Abstract

Since 2014, Formula 1 engines have been turbocharged spark-ignited engines. In this scenario, the maximum engine power available in full-load conditions can be achieved only by optimizing combustion phasing within the cycle, i.e., by advancing the center of combustion until the limit established by the occurrence of abnormal combustion. High in-cylinder pressure peaks and the possible occurrence of knocking combustion significantly increase the heat transfer to the walls and might generate hot spots inside the combustion chamber. This work presents a methodology suitable to properly diagnose and control the occurrence of pre-ignition events that emanate from hot spots. The methodology is based on a control-oriented model of the ignition delay, which is compared to the actual ignition delay calculated from the real-time processing of the in-cylinder pressure trace. When the measured ignition delay becomes significantly smaller than that modeled, it means that ignition has been activated by a hot spot instead of the spark plug. In this case, the presented approach, implemented in the electronic control unit (ECU) that manages the whole hybrid power unit, detects a pre-ignition event and corrects the injection pattern to avoid the occurrence of further abnormal combustion.

Time-Optimal Low-Level Control and Gearshift Strategies for the Formula 1 Hybrid Electric Powertrain

https://www.mdpi.com/1996-1073/14/1/171

Abstract

Today, Formula 1 race cars are equipped with complex hybrid electric powertrains that display significant cross-couplings between the internal combustion engine and the electrical energy recovery system. Given that a large number of these phenomena are strongly engine-speed dependent, not only the energy management but also the gearshift strategy significantly influence the achievable lap time for a given fuel and battery budget. Therefore, in this paper we propose a detailed low-level mathematical model of the Formula 1 powertrain suited for numerical optimization, and solve the time-optimal control problem in a computationally efficient way. First, we describe the powertrain dynamics by means of first principle modeling approaches and neural network techniques, with a strong focus on the low-level actuation of the internal combustion engine and its coupling with the energy recovery system. Next, we relax the integer decision variable related to the gearbox by applying outer convexification and solve the resulting optimization problem. Our results show that the energy consumption budgets not only influence the fuel mass flow and electric boosting operation, but also the gearshift strategy and the low-level engine operation, e.g., the intake manifold pressure evolution, the air-to-fuel ratio or the turbine waste-gate position.

Low-level Online Control of the Formula 1 Power Unit with Feedforward Cylinder Deactivation


https://arxiv.org/abs/2303.00372

Since 2014, the Fédération Internationale de l'Automobile has prescribed a parallel hybrid powertrain for the Formula 1 race cars. The complex low-level interactions between the thermal and the electrical part represent a non-trivial and challenging system to be controlled online. We present a novel controller architecture composed of a supervisory controller for the energy management, a feedforward cylinder deactivation controller, and a track region-dependent low-level nonlinear model predictive controller to optimize the engine actuators. Except for the nonlinear model predictive controller, the proposed controller subsystems are computationally inexpensive and are real time capable. The framework is tested and validated in a simulation environment for several realistic scenarios disturbed by driver actions or grip conditions on the track. In particular, we analyze how the control architecture deals with an unexpected gearshift trajectory during an acceleration phase. Further, we demonstrate how an increased maximum velocity trajectory impacts the online low-level controller. Our results show a suboptimality over an entire lap with respect to the benchmark solution of 49 ms and 64 ms, respectively, which we deem acceptable. Compared to the same control architecture with full knowledge of the disturbances, the suboptimality amounted to only 2 ms and 17 ms. For all case studies we show that the cylinder deactivation capability decreases the suboptimality by 7 to 8 ms.

[/quote]


Also Honda. Discusses knock control strategies and how to extract energy out of the exhaust for energy recovery. Remember, the more efficient an engine is, the less energy can be extracted. This forced Honda to go in house to their jet engine people to make the turbo more efficient

Honda’s Engine Review: Volume 13, No 5 (2023) ‘ Special Feature: F1 Power Unit: Technology and Challenges for Winning
　- The Technology and Thoughts Put Into the Power Unit That Won the F1 Championship Title -’
https://www-jsae-or-jp.translate.goog/e ... r_pto=wapp



Also useful to help understand TJI:


Numerical Study on Enhancing Power and Thermal Efficiency of Large Motorcycle Gasoline Engine Using Pre-chamber Jet Combustion Simulated by Combustion CFD

https://www.hondarandd.jp/point.php?pid=1422&lang=en

A study of combustion methods was conducted using 3D combustion simulation with the aim of enhancing power at full load and thermal efficiency at partial load for a big-bore spark ignition gasoline engine for large motorcycles. The effect of passive pre-chamber jet combustion on power was confirmed at full load. It was further confirmed that a jet sprayed from the pre-chamber into the main chamber caused an increase in turbulent kinetic energy that sped up combustion, and that increasing the compression ratio from 10.1 to 12.1 resulted in an enhancement of 3.6% in indicated work at full load compared to conventional SI combustion. At partial load, the effect of pre-chamber jet 2plug combustion, achieved by ignition in the pre-chamber after the ignition of the main-chamber side-plug with the aim of enhancing combustion stability, was confirmed. The jet sprayed from the pre-chamber facilitates ignition by coming into contact with the flame surface generated by the earlier ignition of the main-chamber side-plug. It was confirmed that this resulted in an increase in indicated thermal efficiency of 1.7 points at partial load compared to conventional SI combustion.

[diffuser]

I am not so sure if a slightly higher ICE efficiency will really be decisive. Yes, a few extra kJ in the acceleration phase will mean extra kJs recovered, meaning in the next straight you have extra electrical energy as well. Also it will give more battery charging in the off throttle phases.
BUT better aero efficiency will have exactly the same effect. Less energy lost in acceleration and coasting phases will mean more recovery, less drag in off throttle phases will mean more opportunity to charge the battery.
The same goes for electrical efficiency, and even mechanical grip helps.

"slightly" is a word that can mean many things to different people. If I define "slightly" as being able to start Silverstone with 10kg of less fuel than everyone else, yet still have the same power and range. That is huge.

[mzso]

Ah ha, yes, that is the piece of information I was missing, so yes. Steel is allowed according to that rule.

Also by the meanings of the words steel and iron alloy.

Nope.

Steel is an alloy.
Iron can be both, it can be cast or an alloy. But what most people think of as cast iron, is actually an alloy.

Steel is an iron alloy. Cast iron is a different iron alloy. You're arguing about nothing.

[Hoffman900]

Who tf cares how “steel” is defined. Without knowing the exact composition of Ferrari’s unsubstantiated rumors concerning their head, this just just a giant circle jerk.