2025/2026 Hybrid Powerunit speculation

[Holm86]

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

Wait.. what? It's banned?? Is that an effort to cut cost due to stabilising a very high RPM part across the distance of the V vs hot/cold being right next to one another?

This is the regulation that basically bans split turbochargers:

Referring to Drawing 4 of Appendix C3, the turbocharger compressor and turbine must satisfy the
following dimensional constraints. Only compressor and turbine wheels approved by the FIA
Technical Department will be allowed:

a. The compressor exducer blade outer diameter (A) must lie between 100mm and 110mm. For
the avoidance of doubt, no part of the compressor wheel (including blades, hub and any
blade/hub fillet radius) can have a diameter more than the upper limit and the maximum
diameter of the compressor wheel (including blades, hub and any blade/hub fillet radius)
cannot have a diameter smaller than the lower limit.
b. The compressor axial distance from the outside diameter of the inducer blade edge to rear
plane of exducer, at its outer diameter (B) must lie between 30mm and 35mm
c.
The turbine inducer blade outer diameter (C) must lie between 90mm and 100mm. For the
avoidance of doubt, no part of the turbine wheel (including blades, hub and any blade/hub fillet
radius) can have a diameter more than the upper limit and the maximum diameter of the
turbine wheel (including blades, hub and any blade/hub fillet radius) cannot have a diameter
smaller than the lower limit.
d. The turbine axial distance from the outside diameter of the exducer blade edge to forward
plane of inducer, at its outer diameter (D) must lie between 35mm and 40mm
e.
The maximum distance between the rear of the compressor exducer and the front of the
turbine inducer (E) will be 175mm

https://www.fia.com/sites/default/files ... -12-11.pdf

[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?