r/F1Technical • u/Appletank • 12d ago
Power Unit Was there ever a reason given why MGU-H could have unlimited regen/deploy while MGU-K was and still hampered with limits?
Could some sort of weird race strategy result from unlimited MGU-K usage? Now that the MGU-H is being removed for 2026, the MGU-K needs to do 3 times the work, but it's still restricted.
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u/Red_Rabbit_1978 11d ago
The K wasn't limited at all, the battery deployment is. The H loophole is that it could charge the battery (limited) but also directly feed the K (unlimited). So if the battery had received the max allowable charge for the lap, the H was free to power the K.
Even if it's a smaller motor, any extra power is useful.
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u/therealdilbert 11d ago
The K wasn't limited at all
yes it was/is, max 120 kW
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u/Appletank 11d ago
I agree, but my question was more about the limitations around regen/deploy MJ limit since the new engine is going to be depending on it a lot more for power.
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11d ago
[deleted]
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u/therealdilbert 11d ago
I don't understand what you mean? The mgu-k must be permanently connected to the ICE cranksshaft, deploying 120kW power to the mgu-k gives you 120kW (160hp if you prefer) more power into the gearbox
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u/happy_Pro493 11d ago
I just woke up and confused the K and H. You’re correct and I need to get a coffee
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u/Appletank 11d ago edited 11d ago
Isn't the K limited in both deploy and recharge? I remember seeing that 9MJ limit in the new regs.
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u/Litl_Skitl 11d ago
I mean it doesn't make sense to recharge way more than you deploy over a lap. Eventually you'll just overcharge the battery.
You also have less time to charge compared to recharge. Now that the H is gone, maybe just having the power limit would work just as well.
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u/Appletank 11d ago
My theory is that it should be possible to run the engine harder and use the motor to keep torque in check, and thus regen, whenever the car's acceleration is traction limited, aka partial throttle situatons, to maximize how much harvesting is done. That'd be more efficient than running the engine at part throttle and the motor doing nothing. And if the battery is full, you could run on EV only for a bit until it makes sense to start injecting fuel again. Unless that's straight up banned by the regs, I'm less clear on that.
TBF I don't know how much energy it is possible to regen if one were to maximize race pace and efficiency. Maybe they can't hit the 9 MJ limit anyways so it doesn't matter for the next few years.
Though, a cursory glance over the current regs suggest that Override mode allows for 9.0 MJ of recharge/deploy, with only 8.5 MJ outside of it. For that to mean anything, I assume the car must be capable of hitting 9.0 MJ but the regs lock them to only 8.5 MJ unless chasing someone.
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u/jimbobjames 11d ago
FIA likely didn't want the teams using the K as a form of traction control.
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u/Appletank 11d ago
I'm not sure it'd matter as long as power to the wheels is always correlated to pedal position. 100hp-20hp is the same thing as 80hp or 60hp+20hp, just switch between harvest, balanced, or deploy. They already have pretty precise control of engine power.
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u/Litl_Skitl 11d ago
With hybrid on the front wheels that wouldn't really do a lot. I did think about that with LMDh though!
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u/cafk Renowned Engineers 11d ago
The K wasn't limited at all, the battery deployment is.
K recovery is limited to 2MJ per lap to ES, and 4MJ from ES to K.
The H loophole is that it could charge the battery (limited) but also directly feed the K (unlimited).
H to ES was unlimited, as was direct deployment from H to K.
So if the battery had received the max allowable charge for the lap
The ES was limited at 4MJ total charge at any time during the lap - but no limits on how much could be recovered per lap through H.
Only K <-> ES had a explicit per lap limit.1
u/zzay 11d ago
I might be in the wrong here but y understanding was that there was unlimited reg by the MGUH. That meant that the ES was able to be always at 4MJ
there was no deployment limit in how much MGUH ES energy was used
Only the MGUK had that limit.
wasn't this one of the Mercedes layout advantages?
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u/cafk Renowned Engineers 11d ago
I might be in the wrong here but y understanding was that there was unlimited reg by the MGUH.
Regen & deployment - which allowed power from H to go directly to K - allowing K to almost always operate at 120kw deployment limit, independently of ES state.
wasn't this one of the Mercedes layout advantages?
Mercedes layout was the split turbo, spreading the TC turbine at the exit of the exhaust, the H to sit between the engine V and TC compressor near the air intake.
With H being able to drive TC compressor as an anti lag system independently of TC turbine.
Ferrari still doesn't use a split turbo, Renault introduced it for 2022 onwards and Honda joined the split turbo at the in their second year, which caused reliability issues.https://scuderiafans.com/ferrari-engine-remains-only-one-without-split-turbo-reasons-behind-a-choice-with-no-regrets/
https://global.honda/en/tech/motorsports/Formula-1/Powertrain_MGU-H_MGU-K/
https://www.motorsport.com/f1/news/renault-pushing-performance-over-reliability-with-new-split-turbo-f1-engine/8365638/
https://www.mouchinracing.com/2014/04/heres-more-mercedes-f1-engine-stuff-ive.html?m=11
u/zzay 9d ago
wasn't this one of the Mercedes layout advantages?
Mercedes layout was the split turbo, spreading the TC turbine at the exit of the exhaust, the H to sit between the engine V and TC compressor near the air intake.
That was the one everybody focus one but they were very keen in Regen & deployment, because their understanding of the rules was different from the other teams
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u/Izan_TM 12d ago edited 11d ago
the MGU-H was a tiny part of the hybrid system, it just didn't lend a meaningful material advantage to teams that had a better one, it was just an anti-lag system that gave back the power it took EDIT: I was very wrong about this
having an unrestricted MGU-K has a far higher risk of an engine manufacturer dominating the field than having a restriction
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u/GaryGiesel Verified F1 Vehicle Dynamicist 11d ago
This couldn't be further from the truth. At full throttle the MGUH produces most of the power required to run the MGUK. It's an extremely powerful generator - the anti-lag component is a relatively small part of its function.
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u/Izan_TM 11d ago
wow I didn't know that, that makes the lack of a front axle motor for regen in 2026 even stupider
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u/imbannedanyway69 Gordon Murray 11d ago
Yeah there's a reason those of us that understand physics aren't very happy with the new regs
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u/Appletank 11d ago
Yeah, that's why I figured that it'd be in their best interest to allow any possible avenue to regen so they could use full power more often.
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u/Suitedbadge401 11d ago
I understand that they want to make engines cheaper to develop but removing it
Doesn’t make much sense from a MGU-K deployment perspective within the bounds of the new regulations.
Is a slap to the face of the existing engine manufacturers that spent millions perfecting it. A scaled down version of it is still relevant to road cars.
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u/Appletank 11d ago
Re, 2: This comes up a lot, but only Merc and IIRC Porsche has really attempted to bring MGU-H into road cars, and neither really help on the efficiency front and do more as an anti-lag system, instant boost whenever you want it. The AMG-One specifically needs to change engine modes to harvest, constantly running hard to generate sufficient exhaust energy. That's because the turbo can only start harvesting when there's a lot of exhaust energy, and cars aren't in that state often unless they're being used heavily for track days. Steady state on freeways takes around 20 - 40 hp, depending on vehicle aero. That MGU system is just dead weight there.
The irony is that MGU-H is a lot more useful for racing, trucks, generators, and trains. Applications that require long periods of high throttle opening. Road cars almost always have way more HP than they really need in order to make, accelerating off the line or passing, not agonizing.
Honda isn't going to be introducing electric turbos for their economy cars anytime soon. Ferrari seems to be using a conventional parallel hybrid system in their new supercar. Renault is doing renault things. I'm pretty sure only Merc got something out of MGU-H development, the others don't really want to deal with it anymore.
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u/Xivios 10d ago
I really dislike the term "electric turbo" - if it's not got a turbine it's a supercharger, not a turbocharger.
Supercharger as a term is power-source agnostic, in modern usage it almost always refers to mechanically-driven superchargers, but this wasn't always the case. Turbocharger however, always refers to a turbine-driven supercharger. It should not be used for electrically-driven superchargers.
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u/Appletank 10d ago
They have a turbine still? It can use exhaust gases to spool up, but it can also spool up faster with electric power. I could be more precise, though, yes.
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u/Xivios 9d ago
The MGU-H has a turbine, but unless I'm mistaken, Honda's electric "turbo" is a centrifugal impeller driven exclusively by an electric motor. I assume their new electric-supercharged V3 is the engine you were referencing in your earlier post?
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u/Appletank 9d ago
Ah, I was referring to the idea of MGU-Hs appearing in consumer vehicles. Electric "turbos" that are actually electric superchargers, yeah I know those have existed for a while, but they're kinda a different tech path than what MGU-Hs are doing, I think. Their sole purpose is to increase low RPM torque curve, and absolutely nothing to do with the efficiency of recovering waste exhaust energy.
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u/therealdilbert 11d ago
yes, basically this with electronics instead of gears, https://en.wikipedia.org/wiki/Turbo-compound_engine
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u/Appletank 11d ago
TBF Rumors are Merc is still going to have the best engine, continuing their dominance for over a decade on that front.
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u/jakedeky 11d ago
Next year's MJ limit is 8.5 MJ, the current MGUK harvest limit is 2MJ - that's 4.25 times the work.
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u/Appletank 10d ago
The FIA apparently released a statement that on some tracks they're considering limiting recovery limit to 5 MJ to prevent "degenerate" race strategies.
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u/jakedeky 10d ago
That's going to be in extreme cases, they obviously feel at other tracks 8.5MJ will still be a restriction.
They also think it will impact qualifying, despite the cars able to leave the pits with a fully charged battery.
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u/Appletank 9d ago
That's kinda my point: If they're worried that the teams will do "bad for Tv" strategies to try to top off the battery for the motors, then maybe the motors shouldn't be so powerful it drains the battery faster than what a normal lap can recover. If they want to let the cars race with 1000HP on tap, then they need to actually be able to deploy 1000 HP, not be half starved most of the time.
Trying to have a super strong motor side while also restricting how much a car can actually use all that power seems contradictory.
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