2025/2026 Hybrid Powerunit speculation

[michl420]

Aren`t that very small dimensions for the turbo?

[gruntguru]

Aren`t that very small dimensions for the turbo?

No. Those are dimensions of the rotating parts. This turbocharger https://www.garrettmotion.com/racing-an ... 0-80109mm/ is rated for 1,650 hp and has a compressor wheel diameter of 109 mm.

[basti313]

Without the mgu-h, will they go away from the split turbo? Is it even allowed to change this?

If i remember correctly the split turbo had been banned for 2026, FIA hates innovation

That was not an innovation, that was an expensive loop hole without any technical relevance outside of its hole. The error was not to ban it in 2015 or 2016.

Under the latest version of the regulations posted by the FIA there will be 8 forward gears.

I had expected them to reduce the number of gears, perhaps to 6.

Fewer gears would save some weight, but would also means that the engines would have to run to higher rpm in order to stay in the peak power range.

I do not think they can do this for gear span reasons. With fixed gear ratios it is simply impossible to cover all tracks with just one set.
Lowering the number of gears would need to lift the gear ratio fixing...I never understood why they are so eager to fix this to 1...would be enough to allow them ratios which need to be selected before the weekend.

[wuzak]

They could have had 6 forward gears and a set number of final drive ratios from which to choose.

[Martin Keene]

Aren`t that very small dimensions for the turbo?

No. Those are dimensions of the rotating parts. This turbocharger https://www.garrettmotion.com/racing-an ... 0-80109mm/ is rated for 1,650 hp and has a compressor wheel diameter of 109 mm.

Indeed. For a 1.6L engine that turbocharger is massive!

[BassVirolla]

Technically, the ICE=Internal Combustion Engine, will not changing that much. The MGU-H, MGU-K and the turbo are all separate entities and part of the PU. How it will be used is gonna change alot though.

I think the manufacturers will dive even deeper in the Miller cicle, reducing the amount of blowdown and back pressure, now that the MGUH will not be there anymore.

I think that we will see ICEs running much more time at full power with the MGUK recovering while under partial throttle (i.e. partial torque demand from the PU), and emphasis put in even leaner combustion and efficient turbines (while until now the emphasis was put in efficient compressors maximizing the power available to the MGUH and thanks to the MGUH accounting for lag / boost threshold.

I can be totally wrong, but it's my gut feeling.

Mods, move it if you think you should. Totally off topic, but in line with the discussion.

Think you're right. I just don’t see any turbo lag. I doudt they'll let the ICE drop to a rpm where it doesn't have boost built up.

Dragging this from the Aston Martin thread; it looks like a nice matter to discuss:

Given that the boost threshold is rpm dependant and lag is load dependant:

Could we see ICE that barely get totally off-throttle and/or below boost threshold attempting to be more like a generator rather than a vehicle engine? Something along the lines of a locomotive diesel generator?

There's anything in the rules that prevent totally disengage the engine from the transmission while stay clutched to the MGUK, and keep the ICE in generator mode, while lifting but not braking?

Keeping the MGUK charging but not dramatically slowing the car (sort of lift & coast).

[Tommy Cookers]

.... anything in the rules that prevent totally disengage the engine from the transmission while stay clutched to the MGUK, and keep the ICE in generator mode, while lifting but not braking?
Keeping the MGUK charging but not dramatically slowing the car (sort of lift & coast).

yes there is
the PU output torque (ie after crankshaft/MGU-K mixing) must accord with the accelerator/PU output map rules
this cannot happen if the clutch is disengaged ie clutch disengagement time is limited to some milliseconds

the better question might be ....
what generation can be done with the clutch engaged ?

[BassVirolla]

.... anything in the rules that prevent totally disengage the engine from the transmission while stay clutched to the MGUK, and keep the ICE in generator mode, while lifting but not braking?
Keeping the MGUK charging but not dramatically slowing the car (sort of lift & coast).

yes there is
the PU output torque (ie after crankshaft/MGU-K mixing) must accord with the accelerator/PU output map rules
this cannot happen if the clutch is disengaged ie clutch disengagement time is limited to some milliseconds

the better question might be ....
what generation can be done with the clutch engaged ?

Note that I'm talking about ICE, not complete PU.

If torque demand is zero, net output of PU can be zero if all ICE power (as "instantaneous power"; not necessarily "full power") is recovered in MGUK.

And why is disengagement of clutch limited to some ms? What prevents to hold the clutch manually while L&C?

[diffuser]

.... anything in the rules that prevent totally disengage the engine from the transmission while stay clutched to the MGUK, and keep the ICE in generator mode, while lifting but not braking?
Keeping the MGUK charging but not dramatically slowing the car (sort of lift & coast).

yes there is
the PU output torque (ie after crankshaft/MGU-K mixing) must accord with the accelerator/PU output map rules
this cannot happen if the clutch is disengaged ie clutch disengagement time is limited to some milliseconds

the better question might be ....
what generation can be done with the clutch engaged ?

Note that I'm talking about ICE, not complete PU.

If torque demand is zero, net output of PU can be zero if all ICE power (as "instantaneous power"; not necessarily "full power") is recovered in MGUK.

And why is disengagement of clutch limited to some ms? What prevents to hold the clutch manually while L&C?

Aren't we just talking about accelerating with the rear brakes on?

[BassVirolla]

yes there is
the PU output torque (ie after crankshaft/MGU-K mixing) must accord with the accelerator/PU output map rules
this cannot happen if the clutch is disengaged ie clutch disengagement time is limited to some milliseconds

the better question might be ....
what generation can be done with the clutch engaged ?

Note that I'm talking about ICE, not complete PU.

If torque demand is zero, net output of PU can be zero if all ICE power (as "instantaneous power"; not necessarily "full power") is recovered in MGUK.

And why is disengagement of clutch limited to some ms? What prevents to hold the clutch manually while L&C?

Aren't we just talking about accelerating with the rear brakes on?

No, I think in lift & coast with clutch disengaged and ICE running for MGUK recovery.

Of course, matching ICE power with MGUK generating, net output torque would be zero while the driver has the throttle pedal lifted.

[wuzak]

Note that I'm talking about ICE, not complete PU.

If torque demand is zero, net output of PU can be zero if all ICE power (as "instantaneous power"; not necessarily "full power") is recovered in MGUK.

And why is disengagement of clutch limited to some ms? What prevents to hold the clutch manually while L&C?

Aren't we just talking about accelerating with the rear brakes on?

No, I think in lift & coast with clutch disengaged and ICE running for MGUK recovery.

Of course, matching ICE power with MGUK generating, net output torque would be zero while the driver has the throttle pedal lifted.

The amount of fuel flow is further restricted when the driver is off throttle. The lower the torque demand is, teh lower the fuel flow is allowed.

In lifting and coasting, the MGUK can potentially recover 350kW.

On full throttle, the maximum MGUK recovery is 100kW.

Also, disconnecting the drive from the PU using the clutch in lift and coast sort of defeats the purpose of the ERS.

Clutch operation by the ECU is limited to gearshifts, and the time is limited to prevent them using it for TC, or other.

It could be operated manually, but coordinating that with the engne controls would be difficult - the driver can't just prss on the throttle, as that gives a certain torque demand which has to be sent to the rear wheels.

[BassVirolla]

Aren't we just talking about accelerating with the rear brakes on?

No, I think in lift & coast with clutch disengaged and ICE running for MGUK recovery.

Of course, matching ICE power with MGUK generating, net output torque would be zero while the driver has the throttle pedal lifted.

The amount of fuel flow is further restricted when the driver is off throttle. The lower the torque demand is, teh lower the fuel flow is allowed.

In lifting and coasting, the MGUK can potentially recover 350kW.

On full throttle, the maximum MGUK recovery is 100kW.

Also, disconnecting the drive from the PU using the clutch in lift and coast sort of defeats the purpose of the ERS.

Clutch operation by the ECU is limited to gearshifts, and the time is limited to prevent them using it for TC, or other.

It could be operated manually, but coordinating that with the engne controls would be difficult - the driver can't just prss on the throttle, as that gives a certain torque demand which has to be sent to the rear wheels.

In my mind it was a sort of "zero torque net output" recovery mode, possibly configurated with the clutch manually pressed while moving (not pushing the throttle pedal, but automatically accelerating the ICE vs. MGUK load until a net zero torque in the full PU).

Only sense it would possibly have would be a L&C with less speed losing that if you put 350kw of rear braking.

The 100kW limit under full torque demand would not apply while lifting.

What's the fuel limit while off throttle?

[wuzak]

C5.4.5 At partial load, the fuel energy flow must not exceed the limit curve defined below:
EF (MJ/h) = 380 when the engine power is equal to or below -50kW
EF (MJ/h) = 9.78 x engine power (kW) + 869 when the engine power is above -50kW

[BassVirolla]

C5.4.5 At partial load, the fuel energy flow must not exceed the limit curve defined below:
EF (MJ/h) = 380 when the engine power is equal to or below -50kW
EF (MJ/h) = 9.78 x engine power (kW) + 869 when the engine power is above -50kW

Engine refers to full PU or ICE alone? Because I see no sense in the ICE producing minus 50kW.

I understand that the fuel at complete PU power = 0W (ICE vs MGUK for net zero) would be 869MJ/h, which amounts to 241,8kW of gross available power.

If the PU efficiency is nearing 50% (which we cannot know, at least right now), putting the ICE vs. MGUK with clutch disengaged and none torque request from the driver, it would be possible to harvest at 120kW. Not negligible!

Even then, the wording says "at partial load". What's the definition of load? Torque request ≠ load? Load on the ICE? Load in the full PU?

If the driver don't push on the throttle, could be accounted as another scenario not under " partial load", I suppose.

[Tommy Cookers]

C5.4.5 At partial load, the fuel energy flow must not exceed the limit curve defined below:
EF (MJ/h) = 380 when the engine power is equal to or below -50kW
EF (MJ/h) = 9.78 x engine power (kW) + 869 when the engine power is above -50kW

Engine refers to full PU or ICE alone? Because I see no sense in the ICE producing minus 50kW.
I understand that the fuel at complete PU power = 0W (ICE vs MGUK for net zero) would be 869MJ/h, which amounts to 241,8kW of gross available power.
If the PU efficiency is nearing 50% (which we cannot know, at least right now), putting the ICE vs. MGUK with clutch disengaged and none torque request from the driver, it would be possible to harvest at 120kW. Not negligible!
Even then, the wording says "at partial load". What's the definition of load? Torque request ≠ load? Load on the ICE? Load in the full PU?
If the driver don't push on the throttle, could be accounted as another scenario not under " partial load", I suppose.

-50 kW or below is the ICE power (accelerator-off) for rpms above idle - ie so-called 'engine braking'
engine power means ICEngine power not Power Unit power

clutch-disengaged or clutch-engaged the energy sum is the same