2025/2026 Hybrid Powerunit speculation

[Tommy Cookers]

...wouldn't it be advantageous to have multiple, smaller turbos anyway? (I'm guessing 2 or 3 might be viable with a V6)

Packaging and, to a little amount, turbo lag is somewhat better to have twin turbos. But a single larger turbo is more efficient.

a single larger turbo is more efficient only if the exhaust pulses (waves) have by design been cancelled (not preserved)
we stopped doing that 50 years ago
preserved exhaust pulses can significantly or substantially drive the turbo without back pressure
ok 2026 F1 has unusually high expansion ratio and unusually lean AFR so turbine work relative to demand will be low

a V6 is crying out for 2 turbos
because the exhaust pulses are ideal with each bank of 3 cylinders having its own turbo
(ok slightly less than ideal with a 90 deg V6)

[saviour stivala]

Exhaust gasses drives the turbocharger turbine with back-pressure. It is an inherent part of the turbocharging process, not something that is avoided. The difference in pressure between the exhaust manifold (pre-turbine) and the exhaust pipe (post-turbine) is what causes the turbine to spin. This pressure to flow creates back pressure in the exhaust manifold. Without this back pressure in the exhaust manifold when the waste-gate/s is/are open (free-load-mode) the formula one ICE produces the most power.

[BassVirolla]

...wouldn't it be advantageous to have multiple, smaller turbos anyway? (I'm guessing 2 or 3 might be viable with a V6)

Packaging and, to a little amount, turbo lag is somewhat better to have twin turbos. But a single larger turbo is more efficient.

a single larger turbo is more efficient only if the exhaust pulses (waves) have by design been cancelled (not preserved)
we stopped doing that 50 years ago
preserved exhaust pulses can significantly or substantially drive the turbo without back pressure
ok 2026 F1 has unusually high expansion ratio and unusually lean AFR so turbine work relative to demand will be low

a V6 is crying out for 2 turbos
because the exhaust pulses are ideal with each bank of 3 cylinders having its own turbo
(ok slightly less than ideal with a 90 deg V6)

While I can and should aknowledge it, it's just true for the turbine. For the compressor, still better one big than two small.

[BassVirolla]

...wouldn't it be advantageous to have multiple, smaller turbos anyway? (I'm guessing 2 or 3 might be viable with a V6)

Packaging and, to a little amount, turbo lag is somewhat better to have twin turbos. But a single larger turbo is more efficient.

a single larger turbo is more efficient only if the exhaust pulses (waves) have by design been cancelled (not preserved)
we stopped doing that 50 years ago
preserved exhaust pulses can significantly or substantially drive the turbo without back pressure
ok 2026 F1 has unusually high expansion ratio and unusually lean AFR so turbine work relative to demand will be low

a V6 is crying out for 2 turbos
because the exhaust pulses are ideal with each bank of 3 cylinders having its own turbo
(ok slightly less than ideal with a 90 deg V6)

Thus, it should be noted that pure pulse turbocharging requires a turbine size which has to be designed only for the single cylinder displacement, while a pure constant pressure turbocharging requires a turbine size depending only on the total displacement of the engine.

https://link.springer.com/article/10.10 ... 19-00048-8

I've still haven't read it completely, but all points to 4 cylinder per turbine being better than 2 or 3, at least in some simulations.

I much doubt that there is an "ideal" cylinder count, but more likely an ideal set of variables (rpm, turbine size, housing size, manifold size, ...).

Edit: some pages more into the article, it is explained that the speed component of the exhaust pressure amounts to less than a 2% (while talking about turbine work).

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

Truly an insightful read. If you, fellow members, are inclined to engines, turbocharging or merely thermodynamics, is quite interesting.

[Tommy Cookers]

Thus, it should be noted that pure pulse turbocharging requires a turbine size which has to be designed only for the single cylinder displacement, while a pure constant pressure turbocharging requires a turbine size depending only on the total displacement of the engine.
https://link.springer.com/article/10.10 ... 19-00048-8

....the speed component of the exhaust pressure amounts to less than a 2% (while talking about turbine work).

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

yes
turbocharging is the dutiful son of the (so-called) Diesel engine, its practicalities, and the exhaust gas thereof

preserving the exhaust 'pulses' is in principle unrelated to 'tuned length' exhausts
as WW2 and later piston-engined aircraft showed
either the 'TurboCompound' (18 pipe 3 turbine recovery power driving the crankshaft/propeller shaft) ....
or direct momentum addition to the ambient air by entrainment ('jet effect') - 12, 14, 18 or 24 'stub' pipes 'fishtailed'
either was 'free' power - not power gained by increasing mass flow of air and fuel
there was no backpressure (except when engineered to enhance jet thrust for some particular situation)

Pinkel of the NACA Lewis Propulsion Laboratory c. 1941 was the real brains in this field ....
all the rest were blinkered and wrong in their thinking

of course the engines all had eg 6 or 7:1 CR to allow high boost for high takeoff power ....
so there was a lot of energy potential left in those pulses


by 2015 all the F1 engines had already or adopted the 'pulse tuned length' exhaust system
for 2026 will they throw away this seemingly 'free power' ?

[vorticism]

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

I'd say they're for improving *both scavenging and pulse velocity--which is the greater beneficiary I'm not sure. In a log manifold the pulse is expanded across the shared volume of the log rather than directed exclusively toward the turbine. Some of the initial F1 turbo-hybrid engines had log manifolds which to me suggests scavenging wasn't necessarily an issue as boost pressure and valve overlap could clear out the cylinder; use of Miller-cycle would support such a pressure gradient existing during overlap. Log manifolds are smaller and lighter, which may have been the initial use case.

[Holm86]

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

I'd say they're for improving *both scavenging and pulse velocity--which is the greater beneficiary I'm not sure. In a log manifold the pulse is expanded across the shared volume of the log rather than directed exclusively toward the turbine. Some of the initial F1 turbo-hybrid engines had log manifolds which to me suggests scavenging wasn't necessarily an issue as boost pressure and valve overlap could clear out the cylinder; use of Miller-cycle would support such a pressure gradient existing during overlap. Log manifolds are smaller and lighter, which may have been the initial use case.

Mercedes used log style manifolds in the first year of the turbo hybrid era, I think they chose this for space optimization. They also sounded quite different.

But does equal length manifolds really make sense in an odd fire engine?? A 90° V6 with shared crank pins fires in a 90-150-90-150-90-150 order, wouldn't unequal length exhaust pipes make it possible to space out exhaust pulses more even at a given RPM?? Has any team tried this??

[BassVirolla]

Thus, it should be noted that pure pulse turbocharging requires a turbine size which has to be designed only for the single cylinder displacement, while a pure constant pressure turbocharging requires a turbine size depending only on the total displacement of the engine.
https://link.springer.com/article/10.10 ... 19-00048-8

....the speed component of the exhaust pressure amounts to less than a 2% (while talking about turbine work).

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

yes
turbocharging is the dutiful son of the (so-called) Diesel engine, its practicalities, and the exhaust gas thereof

preserving the exhaust 'pulses' is in principle unrelated to 'tuned length' exhausts
as WW2 and later piston-engined aircraft showed
either the 'TurboCompound' (18 pipe 3 turbine recovery power driving the crankshaft/propeller shaft) ....
or direct momentum addition to the ambient air by entrainment ('jet effect') - 12, 14, 18 or 24 'stub' pipes 'fishtailed'
either was 'free' power - not power gained by increasing mass flow of air and fuel
there was no backpressure (except when engineered to enhance jet thrust for some particular situation)

Pinkel of the NACA Lewis Propulsion Laboratory c. 1941 was the real brains in this field ....
all the rest were blinkered and wrong in their thinking

of course the engines all had eg 6 or 7:1 CR to allow high boost for high takeoff power ....
so there was a lot of energy potential left in those pulses


by 2015 all the F1 engines had already or adopted the 'pulse tuned length' exhaust system
for 2026 will they throw away this seemingly 'free power' ?

Why would they throw it away?

I'm not arguing with (against) anybody, just adding relevant info to the thread with the aim of get a bigger picture.

As Vorticism well points, log manifolds have been tested and ditched.

Which (with your mention of the WW2 pulse preservation) adds even more to my point: Tuned lengths are more a thing of aiding the ICE rather than the turbo.

Nevertheless, we are heavily drifting away from the matter about compressor and / or turbine sizes (and I like it!).

[BassVirolla]

So, probably tuned length exhausts in F1 are more related to cylinder scavenging than turbine work.

I'd say they're for improving *both scavenging and pulse velocity--which is the greater beneficiary I'm not sure. In a log manifold the pulse is expanded across the shared volume of the log rather than directed exclusively toward the turbine. Some of the initial F1 turbo-hybrid engines had log manifolds which to me suggests scavenging wasn't necessarily an issue as boost pressure and valve overlap could clear out the cylinder; use of Miller-cycle would support such a pressure gradient existing during overlap. Log manifolds are smaller and lighter, which may have been the initial use case.

Mercedes used log style manifolds in the first year of the turbo hybrid era, I think they chose this for space optimization. They also sounded quite different.

But does equal length manifolds really make sense in an odd fire engine?? A 90° V6 with shared crank pins fires in a 90-150-90-150-90-150 order, wouldn't unequal length exhaust pipes make it possible to space out exhaust pulses more even at a given RPM?? Has any team tried this??

Uneven lengths for even pulse spacing.
Even lengths for cylinder scavenging (exhaust tuned for rpms).

[Tommy Cookers]

what I write whenever this topic comes up ......

each bank and its 3 equal branch manifold is an island (of equal 240 deg firing)
what matters is to make the pipes beyond each manifold different to each other in length
by enough to compensate for the inequality in firing times (this can only be exactly correct at one rpm)
about 20 cm difference IIRC
the early Renault turbo F1 did this (for about 18 months before the twin turbo came along)

[BassVirolla]

what I write whenever this topic comes up ......

each bank and its 3 equal branch manifold is an island (of equal 240 deg firing)
what matters is to make the pipes beyond each manifold different to each other in length
by enough to compensate for the inequality in firing times (this can only be exactly correct at one rpm)
about 20 cm difference IIRC
the early Renault turbo F1 did this (for about 18 months before the twin turbo came along)

Without wanting to sound stubborn or defying... Just truly curious and with an insatiable appetite for learning... Probably steaming from my liking for tuning turbo diesel engines.

- What do you think is better in the general picture: Tuned lengths for cylinder efficiency or a manifold made to retain / improve blowdown / pulses?

- Why 3 cylinder better than 4 (or 2) per bank? What makes you say that 3 is the ideal number?

[gruntguru]

what I write whenever this topic comes up ......

each bank and its 3 equal branch manifold is an island (of equal 240 deg firing)
what matters is to make the pipes beyond each manifold different to each other in length
by enough to compensate for the inequality in firing times (this can only be exactly correct at one rpm)
about 20 cm difference IIRC
the early Renault turbo F1 did this (for about 18 months before the twin turbo came along)

Without wanting to sound stubborn or defying... Just truly curious and with an insatiable appetite for learning... Probably steaming from my liking for tuning turbo diesel engines.

- What do you think is better in the general picture: Tuned lengths for cylinder efficiency or a manifold made to retain / improve blowdown / pulses?

- Why 3 cylinder better than 4 (or 2) per bank? What makes you say that 3 is the ideal number?

"Cylinder efficiency or maximum blowdown"
Not sure if they are mutually exclusive. There is probably a runner length that achieves a useful compromise for both (along with packaging of course).

"Why three cylinders?"
Blowdown energy cannot be effectively recovered if more than three cylinders share a manifold. The high pressure blowdown pulse from one cylinder will increase backpressure in the previous cylinder at a disadvantageous time (late in its exhaust phase).

Fewer than three cylinders works OK but will require a smaller turbine which will always be less efficient than a larger one.

[aleks_ader]

Dammn dint know that MGUK needs to be inside survival cell, witch genius had this idea? Quite bad optimisation.

NOTE: edit - WHAT IS OFFICIAL REASOING FOR THAT? That quite bothers me not gonna lie. Why ditch established well known paradigms.

[BassVirolla]

what I write whenever this topic comes up ......

each bank and its 3 equal branch manifold is an island (of equal 240 deg firing)
what matters is to make the pipes beyond each manifold different to each other in length
by enough to compensate for the inequality in firing times (this can only be exactly correct at one rpm)
about 20 cm difference IIRC
the early Renault turbo F1 did this (for about 18 months before the twin turbo came along)

Without wanting to sound stubborn or defying... Just truly curious and with an insatiable appetite for learning... Probably steaming from my liking for tuning turbo diesel engines.

- What do you think is better in the general picture: Tuned lengths for cylinder efficiency or a manifold made to retain / improve blowdown / pulses?

- Why 3 cylinder better than 4 (or 2) per bank? What makes you say that 3 is the ideal number?

"Cylinder efficiency or maximum blowdown"
Not sure if they are mutually exclusive. There is probably a runner length that achieves a useful compromise for both (along with packaging of course).

"Why three cylinders?"
Blowdown energy cannot be effectively recovered if more than three cylinders share a manifold. The high pressure blowdown pulse from one cylinder will increase backpressure in the previous cylinder at a disadvantageous time (late in its exhaust phase).

Fewer than three cylinders works OK but will require a smaller turbine which will always be less efficient than a larger one.

Well, the old Renault single turbo engine would be a case of mutually exclusive with inequal lengths to have even spaced pulses.

[wuzak]

Dammn dint know that MGUK needs to be inside survival cell, witch genius had this idea? Quite bad optimisation.

NOTE: edit - WHAT IS OFFICIAL REASOING FOR THAT? That quite bothers me not gonna lie. Why ditch established well known paradigms.

The answer is that it doesn't.

Being mounted on the survival cell is one option:

C5.18.1 The MGU-K must be mechanically fixed to the Survival Cell, the ICE or both.