2025/2026 Hybrid Powerunit speculation

[vorticism]

So, same amount of fuel to go slower? Any chance that the 70kg/hr fuel flow rate could lead to similar or better thermal efficiency from the ICE? Simply by reducing boost & fuel within the same capacity engine. And will the PU unit as a whole be able to match or surpass the ~50% TE of the current PUs? That would be the ultimate measure. Can these cars run a race with less fuel or not. Otherwise it's a step back in terms of efficiency. It might be hard to tell with the active aero they're adding. If the '26 PUs prove to be less efficient then it seems like their primary design criteria will have to be considered as cost reduction. Like '05 to '06, where the engines became less powerful in the name of cost saving. Some of the magic was lost and that might be the case again.

[diffuser]

So, same amount of fuel to go slower? Any chance that the 70kg/hr fuel flow rate could lead to similar or better thermal efficiency from the ICE? Simply by reducing boost & fuel within the same capacity engine. And will the PU unit as a whole be able to match or surpass the ~50% TE of the current PUs? That would be the ultimate measure. Can these cars run a race with less fuel or not. Otherwise it's a step back in terms of efficiency. It might be hard to tell with the active aero they're adding. If the '26 PUs prove to be less efficient then it seems like their primary design criteria will have to be considered as cost reduction. Like '05 to '06, where the engines became less powerful in the name of cost saving. Some of the magic was lost and that might be the case again.

I'm sure they'll make the new ICE more energy efficient but how do they make up for the loss of efficiency from losing the MGU-H?

[gruntguru]

So, same amount of fuel to go slower? Any chance that the 70kg/hr fuel flow rate could lead to similar or better thermal efficiency from the ICE? Simply by reducing boost & fuel within the same capacity engine. And will the PU unit as a whole be able to match or surpass the ~50% TE of the current PUs? That would be the ultimate measure. Can these cars run a race with less fuel or not. Otherwise it's a step back in terms of efficiency. It might be hard to tell with the active aero they're adding. If the '26 PUs prove to be less efficient then it seems like their primary design criteria will have to be considered as cost reduction. Like '05 to '06, where the engines became less powerful in the name of cost saving. Some of the magic was lost and that might be the case again.

I'm sure they'll make the new ICE more energy efficient but how do they make up for the loss of efficiency from losing the MGU-H?

Unlikely the new ICE will match the efficiency of the current one. The loss of the MGU-H is significant.

[diffuser]

So, same amount of fuel to go slower? Any chance that the 70kg/hr fuel flow rate could lead to similar or better thermal efficiency from the ICE? Simply by reducing boost & fuel within the same capacity engine. And will the PU unit as a whole be able to match or surpass the ~50% TE of the current PUs? That would be the ultimate measure. Can these cars run a race with less fuel or not. Otherwise it's a step back in terms of efficiency. It might be hard to tell with the active aero they're adding. If the '26 PUs prove to be less efficient then it seems like their primary design criteria will have to be considered as cost reduction. Like '05 to '06, where the engines became less powerful in the name of cost saving. Some of the magic was lost and that might be the case again.

I'm sure they'll make the new ICE more energy efficient but how do they make up for the loss of efficiency from losing the MGU-H?

Unlikely the new ICE will match the efficiency of the current one. The loss of the MGU-H is significant.

Think you meant "Unlikely the new PU will match the efficiency of the current one. The loss of the MGU-H is significant." but I got you.

[gruntguru]

I get your point. It is really only the ICE that converts fuel energy to mechanical - and that includes the turbo-compounding. Current efficiency of 50%+ includes a very minor loss converting turbine energy to electrical.

Does anyone have any thoughts on how the ICE might change and what efficiency might be possible, now that the only source of work is the crankshaft?

My initial thoughts:
1. Later EVO to increase in-cylinder expansion and minimise EGT.
2. Reduce or eliminate EIVC (Miller) to maximise pumping work done on piston during intake stroke. (This will be the sole means of returning recovered exhaust energy to the PU)
3. Larger turbine and housing to reduce backpressure. Minimise wastegating.

[BassVirolla]

... and call it heavily electrified.

but isn't this the 50/50 that we've all been waiting for ? ....

It's so dumb that they got rid of the MGU-H. They should have just made it a standard part. Maybe soemthing that's like Honda's that all 1 piece with the turbo, to keep the price down. That's the MGU-H is a big fuel saver.

Even more when the MGUHs are doing its way into the automotive market.

[BassVirolla]

I get your point. It is really only the ICE that converts fuel energy to mechanical - and that includes the turbo-compounding. Current efficiency of 50%+ includes a very minor loss converting turbine energy to electrical.

Does anyone have any thoughts on how the ICE might change and what efficiency might be possible, now that the only source of work is the crankshaft?

My initial thoughts:
1. Later EVO to increase in-cylinder expansion and minimise EGT.
2. Reduce or eliminate EIVC (Miller) to maximise pumping work done on piston during intake stroke. (This will be the sole means of returning recovered exhaust energy to the PU)
3. Larger turbine and housing to reduce backpressure. Minimise wastegating.

The way to totally avoid wastegating is achieving a steady state as in some old diesel engines, regulated by fuel flow (a.k.a. very lean burning).

Nevertheless, pumping more air to further lean the combustion increases backpressure, increasing the pumping losses.

Seems like a very difficult balance more suited to stationary machines (constant rpm & load).

In respect to EVO, I don't know if it is a good idea to keep some exhaust gas not vented in order to achieve peak efficiency. I doubt it.

With lean combustion and reducing wastegating, could be good idea (?) to have early injection and long valve overlap to:

- good scavenging
- reduce EGT (cold air in exhaust)
- reduce backpressure (reduced compressor work )

Just thinking out loud, in reality I don't have a clue.

[wuzak]

I get your point. It is really only the ICE that converts fuel energy to mechanical - and that includes the turbo-compounding. Current efficiency of 50%+ includes a very minor loss converting turbine energy to electrical.

Does anyone have any thoughts on how the ICE might change and what efficiency might be possible, now that the only source of work is the crankshaft?

My initial thoughts:
1. Later EVO to increase in-cylinder expansion and minimise EGT.
2. Reduce or eliminate EIVC (Miller) to maximise pumping work done on piston during intake stroke. (This will be the sole means of returning recovered exhaust energy to the PU)
3. Larger turbine and housing to reduce backpressure. Minimise wastegating.

3. The size of the turbo is restrcited by the rules.

C5.3.5 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

Not sure how that relates to minimising back pressure.

[wuzak]

There have been some reports that the best ICE will have about 420kW, which is 50.4% TE.

A while back, Tombazis suggested that the PU could have as much as 1,100hp peak power, which would mean ICE power of 470kW and TE of 56%!

[BassVirolla]

I get your point. It is really only the ICE that converts fuel energy to mechanical - and that includes the turbo-compounding. Current efficiency of 50%+ includes a very minor loss converting turbine energy to electrical.

Does anyone have any thoughts on how the ICE might change and what efficiency might be possible, now that the only source of work is the crankshaft?

My initial thoughts:
1. Later EVO to increase in-cylinder expansion and minimise EGT.
2. Reduce or eliminate EIVC (Miller) to maximise pumping work done on piston during intake stroke. (This will be the sole means of returning recovered exhaust energy to the PU)
3. Larger turbine and housing to reduce backpressure. Minimise wastegating.

3. The size of the turbo is restrcited by the rules.

C5.3.5 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

Not sure how that relates to minimising back pressure.

There is no mention to the turbine housing. At such high-ish rpm for maximum fuel flow, we can expect some serious size turbine housing, even more with the torque fill of the mguk (assuming that you can deploy after every corner at the desired rate).

[mzso]

Fuel density is between 720kg/m³ and 785kg/m³.

Energy density is between 38.0MJ/kg and 41.0MJ/kg.

For 3000MJ, the fuel weight is between 78.9kg and 73.2kg.

The volume of fuel will be between 93L (highest energy density and highest SG) and 109L (lowest energy density and lowest SG) depending on those properties.

Means they're gonna have to have tanks that can hold 150 liters? Maybe more? I mean lots of tracks are 65% full throttle and now you'll be burning fuel off full power demand to charge the battery.

I doubt it. The extra weight and volume will be more harmful than useful at some point. And since there are a lot of turns usually, not much extra fuel will be worth it.
Not sure how they will deal with the few outstanding fast circuits. I don't think they can add extra fuel tanks. And for most tracks packaging a lot of empty space is really a negative factor.

[mzso]

I'm sure they'll make the new ICE more energy efficient but how do they make up for the loss of efficiency from losing the MGU-H?

How? The ICE part is mostly the same and they've been working on this for more than a decade.
And the only manufacturer with significant room for improvement stops supplying PUs.

[diffuser]

Fuel density is between 720kg/m³ and 785kg/m³.

Energy density is between 38.0MJ/kg and 41.0MJ/kg.

For 3000MJ, the fuel weight is between 78.9kg and 73.2kg.

The volume of fuel will be between 93L (highest energy density and highest SG) and 109L (lowest energy density and lowest SG) depending on those properties.

Means they're gonna have to have tanks that can hold 150 liters? Maybe more? I mean lots of tracks are 65% full throttle and now you'll be burning fuel off full power demand to charge the battery.

I doubt it. The extra weight and volume will be more harmful than useful at some point. And since there are a lot of turns usually, not much extra fuel will be worth it.
Not sure how they will deal with the few outstanding fast circuits. I don't think they can add extra fuel tanks. And for most tracks packaging a lot of empty space is really a negative factor.

Multiple tanks is not allowed. There isn't a limit in tank size in the new regs. Just a flow rate restriction. I think my math says 93L/hr ish. You can do the math for a 1.5hr race.

[diffuser]

I'm sure they'll make the new ICE more energy efficient but how do they make up for the loss of efficiency from losing the MGU-H?

How? The ICE part is mostly the same and they've been working on this for more than a decade.
And the only manufacturer with significant room for improvement stops supplying PUs.

I'd doubt it will be a big improvement but there will be some improvement. Also the fuel is improving all the time now.

[gruntguru]

I get your point. It is really only the ICE that converts fuel energy to mechanical - and that includes the turbo-compounding. Current efficiency of 50%+ includes a very minor loss converting turbine energy to electrical.

Does anyone have any thoughts on how the ICE might change and what efficiency might be possible, now that the only source of work is the crankshaft?

My initial thoughts:
1. Later EVO to increase in-cylinder expansion and minimise EGT.
2. Reduce or eliminate EIVC (Miller) to maximise pumping work done on piston during intake stroke. (This will be the sole means of returning recovered exhaust energy to the PU)
3. Larger turbine and housing to reduce backpressure. Minimise wastegating.

3. The size of the turbo is restrcited by the rules.

C5.3.5 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

Not sure how that relates to minimising back pressure.

Yes. Those dimensions are more critical to achieving a high tip velocity and hence pressure ratio. Reducing turbine PR (ie backpressure) requires a reduction in tip diameter and/or increase in flow passage CSA (tip height, exducer diameter and turbine housing CSA). (as mentioned by Bass Virolla)