2025/2026 Hybrid Powerunit speculation

[TimW]

.....

if the MGU-K doesn't run at full RPM it can't make full voltage and so the battery will never be fully charged

Incorrect, power electronics takes care of voltage regulation to the battery. There wil be some variation in efficiency but it can charge at any rpm.

[wuzak]

You can reduce the ERS for the turbo V6 and save some weight too.

The difference between the 2026 ICE and a 2013 like V8 is going to be ~30kg.

Lose the ERS altogether and you can save 55kg (ERS components) plus the weight of coolers for the ERS.

The V8 is heavier right ?
The 2025 ICE (V6 1.6L turbo, not including the MGUs) 100KG + 15KG for Turbocharger & ancillaries, total 115KG. If you divide the 100KG by 3 then multiply by 4 to get you V8 weight, it comes out to 133KG but that assume everything else is the same and only gets to 2.13 Liters. So I think the V8 will be more like 140KG - 150KG.

Plus 40KG more fuel at the beginning of the race if we go back to 110KG limit.

Minimum weight of 2025 PU is 151kg. This does not include the battery.

The minimum weight of the MGUK is 7kg and the MGUH is 4kg, so the ICE without the ERS is 140kg.

The minimum weight of the 2026 ICE is 130kg without ERS. This includes the turbo.

The minimum weight of the 2013 V8 was 95kg.

[FW17]

Are there ways of reducing engine braking so that maximum harvesting by the MGU?

Is it possible for compression stroke pressure to be released out through the spark or injector ports?

[saviour stivala]

Engine braking (lift off throttle) adds to the braking force of the brakes, the use of both the brakes and engine resistance will result in more braking force, the more braking force, the more energy harvesting.

[Martin Keene]

Yes, the simplest way is to open the throttles on the overrun during braking.

[FW17]

Yes, the simplest way is to open the throttles on the overrun during braking.

How does that relieve cylinder pressure?

[Tommy Cookers]

Yes, the simplest way is to open the throttles on the overrun during braking.

How does that relieve cylinder pressure?

and ...
what is the turbocharger doing ?
to conserve turbocharger rpm it might be circulating air not compressing it (how the 917 turbo changed our world)
and now it has variable geometry inlet vanes for control without the traditional throttling losses

the 'engine braking' torque is increased at the rear wheels with every downshift below the high gear
so EB is reduced if there is downshifting only at the end of braking (but the MGU-K designers don't like this)

[FW17]

Yes, the simplest way is to open the throttles on the overrun during braking.

How does that relieve cylinder pressure?

and ...
what is the turbocharger doing ?
to conserve turbocharger rpm it might be circulating air not compressing it (how the 917 turbo changed our world)
and now it has variable geometry inlet vanes for control without the traditional throttling losses

the 'engine braking' torque is increased at the rear wheels with every downshift below the high gear
so EB is reduced if there is downshifting only at the end of braking (but the MGU-K designers don't like this)

With every J generated by the MGU possible, engine braking is just a very big loss in this game. Any small advantage in reducing this undesirable effect will yield an additional mili-second of deployment.

[diffuser]

Yes, the simplest way is to open the throttles on the overrun during braking.

How does that relieve cylinder pressure?

and ...
what is the turbocharger doing ?
to conserve turbocharger rpm it might be circulating air not compressing it (how the 917 turbo changed our world)
and now it has variable geometry inlet vanes for control without the traditional throttling losses

the 'engine braking' torque is increased at the rear wheels with every downshift below the high gear
so EB is reduced if there is downshifting only at the end of braking (but the MGU-K designers don't like this)

You're also not injecting any fuel which leaves 8-9% less volume to compress.

[saviour stivala]

The present (2025) fuel volume injected into the cylinder, that makes-up the volume that the cylinder have to compress is around 0.017 of the total volume.

[Tommy Cookers]

well I have posted as recently as last week on the general desirability of reduced engine braking ......
but it seems that we don't really know what has been going on in the twelve seasons 2014-2025

for 2026 the (350 kW) regenerator rate is relative to the prime mover energy rate (the fuel heat rate) increased fourfold
so eg if we have treated 'engine braking' in 2025 then the benefit will be less in 2026
natural 2026 EB would be roughly 30% less than natural 2025 EB (as the 2026 ICE fuel rate is 30% less)

sorry .... but ....
lots seem to be unchanged from 2025 eg the magic 10500 rpm ???
do the 2026 fuelling rules really encourage running below 10500 ??? (didn't the 2025 rules deter that ?)
is less rpm really going to be the answer efficiencywise ? (the rules expect 60000 rpm MGU-Ks - for response I say)
still (200 msec? allowed) downshifts throughout the braking - automatically blipping fuel and MGU-K motor blips?
and of course we have the MG in regeneration from PU inertia on every upshift - this will be greater in 2026
(and 2026 allows 300 KJ energy storage onboard control electronics CE - I think more generous than 2025 ??)

2026 has less aero DF so the regen time available is longer and better matched to the increased regeneration power
but the full power regen window will close earlier ie partial power regen seems inevitable (unlike 2025 imo)

regen can be increased by so-called coasting ...
and surely by the driver eg if using earlier (less than maximum) braking ?
or does the friction brake : regen brake proportioning only accomodate a fixed level of braking ?
and eg what happens when the regen braking cuts out because eg the battery etc is full or overheating ?

[wuzak]

lots seem to be unchanged from 2025 eg the magic 10500 rpm ???
do the 2026 fuelling rules really encourage running below 10500 ??? (didn't the 2025 rules deter that ?)

The maximum fuel flow rate of 3,000MJ/h is from 10,500rpm and above.

C5.2.3 Fuel energy flow must not exceed 3000MJ/h.
C5.2.4 Below 10500rpm the fuel energy flow must not exceed EF(MJ/h)=0.27*N(rpm)+ 165
C5.2.5 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

2026 has less aero DF so the regen time available is longer and better matched to the increased regeneration power
but the full power regen window will close earlier ie partial power regen seems inevitable (unlike 2025 imo)

Yes, the braking times will be longer, but will he peak braking times be shorter?

It is also likely that they will use the MGUK against the ICE near the end when the driver is still at maximum power demand, as is allowed for in the rules.This will slow the cars a bit, and reduce the braking time.

[saviour stivala]

''What happens when the regenerating braking cuts-out, eg the battery is full or overheating?'' The amount of regenerating braking, the level of regenerating which will depend on driver settings, is shared by the MGU-K regenerating 'braking' effect and the rear wheels hydraulics, When the MGU-K regenerating braking cuts-out, the rear wheels hydraulic brakes will take over the full braking torque . The rules mandates that the rear wheels hydraulic brakes without assistance from MGU-K are capable to provide a minimum of 2500 Nm of torque per wheel.

[saviour stivala]

''What happens when the regenerating braking cuts-out, eg the battery is full or overheating?''

The amount of regenerating braking, the level of regenerating which will depend on driver settings, is shared by the MGU-K regenerating 'braking' effect and the rear wheels hydraulics, When the MGU-K regenerating braking cuts-out, the rear wheels hydraulic brakes will take over the full braking torque .

The rules mandates that the rear wheels hydraulic brakes without assistance from MGU-K are capable to provide a minimum of 2500 Nm of torque per wheel.

[Martin Keene]

Yes, the simplest way is to open the throttles on the overrun during braking.

How does that relieve cylinder pressure?

Prevent the engine trying to suck air past a blockage, thus reducing the engine braking effect.