2025/2026 Hybrid Powerunit speculation

[J.A.W.]

The biggest issue with 2-stroke engines IMO, is the stupidly narrow powerband - they would make F1 cars undrivable. I reckon the 80's turbo cars would be more drivable than an NA 2-stroke F1 car!

In point of fact, you'll have to revise that opinion, & actually, its about 180 degrees off course...

A few cases in point: Cosworth sliced a pair of cylinders from its very successful DFV F1 V8
back in the mid `70s - in an attempt to provide Norton with a 4-stroke capable of winning
bike G.P.'s ahead of the newly rampant 2-strokes, but it was a fail, being 'unrideable' tuned-up.

Honda tried again in `79-80, with a radical 'virtual V8' NR500 4-stroke, yet it was 'unrideable''.

Once the FIM allowed 990cc 4-strokes to compete in the 'Senior/500cc' class, Aprilia tried a 3cyl
slice off Cosworth's V10 F1, 'The Cube' - but this too, was... yeah, you guessed it.. 'unrideable'...

Not only did these massive Moto GP machines have to be 'de-rated' specific output-wise,
they also required all manner of electro-mechanical assists, from a back-torque limiting
'slipper' clutch, to traction-control for power-limiting in corners...

See the Honda dyno graph linked below - showing their 2-stroke G.P. bikes from over a 1/4
century ago, current Moto GP bikes are still nowhere near the (non-assisted, as Mick Doohan
pointed out, other than by the rider's proprioception & reaction time skills) power-density of
those Championship-winning 2-stroke G.P. bikes...

https://www.kiwibiker.co.nz/forums/atta ... 1546116747

[djos]

You missed my point, I was talking about the extremely narrow 2 stroke power band, not overall power.

[J.A.W.]

You missed my point, I was talking about the extremely narrow 2 stroke power band, not overall power.

No I didn't...

If you have a proper perusal of those dyno curves, you'll see for yourself.

Formula cars with 4 fat tyres & downforce are much more forgiving of
sudden/brutal powerbands than big heavy bikes...

What is the likely useful powerband of the current F1 cars? 1500-2000rpm?

[djos]

In terms of 2-stroke power bands, as I understand it, it’s also got a very narrow efficiency window.

I don’t think the curves you showed are representative of the driving feel of a 2 stroke.

Yes, a two stroke can be as efficient as a four stroke, but only by increasing its complexity and/or abandoning the well established paradigms driving a need to have a wide power band.

The primary reason designers were interested in two strokes was their simplicity, and the need to add complexity to overcome their challenges eliminated their attractiveness.

Hence OEM’s like Honda advocating for their removal from MotoGP in favour of 4-strokes.

[J.A.W.]

In terms of 2-stroke power bands, as I understand it, it’s also got a very narrow efficiency window.

I don’t think the curves you showed are representative of the driving feel of a 2 stroke.

Yes, a two stroke can be as efficient as a four stroke, but only by increasing its complexity and/or abandoning the well established paradigms driving a need to have a wide power band.

The primary reason designers were interested in two strokes was their simplicity, and the need to add complexity to overcome their challenges eliminated their attractiveness.

Hence OEM’s like Honda advocating for their removal from MotoGP in favour of 4-strokes.

Djos, you'll just have to keep revising your ideas about 2-strokes:

1, Those (kosher) Honda power curves rise sans dips or glitches, so quite evidently they
are not demonstrating any "...narrow efficiency window".

2, That Honda chart shows the 3 types running 125cc cylinders to be quite close in profile,
& even the outlier 250cc cylinder machine offers a "representative...driving feel..." curve.

3, Actually, when Honda's hugely expensive NR500 'virtual V8' program failed, the 'loss of face'
to a dedicated 4-stroke company drove them to repeat a previous winning solution, to use
their 2-stroke racing knowledge accrued in Moto-X G.P. efforts for over a decade.
Indeed, their 1st 500cc FIM World Championship was won on bikes built by the HRC MX team.

4,No way known were Honda's winning 500cc bikes anywhere near the cost/complexity of their
failed 4-stroke NR500, & yet they won by dint of useable power far in excess both max & in
powerband terms (losing only when the HRC engineers tried to 2nd guess the race team/riders).

5, Honda's founder established an ethos for Honda "...as a 4-stroke company", & they lobbied hard
to ensure the FIM/Dorna 'moved the goalposts' to exclude 2-strokes, 1stly by allowing double
the capacity for 4-strokes, then by outright bans.. It was an entirely attitudinal/political thing,
since costs rose hugely, & only factory supported teams could have any chance of a race win.

[Tommy Cookers]

comparisons of 4 stroke vs 2 stroke are utterly false unless cylinder sizes are equal ... because by geometry ....

the 2 stroke benefits disproportionately (in effective port area) from smaller cylinder sizes .....and ....
the 2 stroke loses disproportionately (in effective port area) from larger cylinder sizes
the last-attempt 500cc twin cylinder 2 strokes had 'only' c.140 hp NA because of this
(peakiness ? - both 4 and 2 cylinder GP bikes had 6 speed gearboxes)
also ....
wall-ported engines (2 stroke) cannot benefit in rpm from a high bore:stroke ratio as head-ported engines (4 stroke) can


turbocharged to 8 or 10 bar ? .... well .....
of course the 2 stroke can be wall ported and head ported
and unburnt fuel leaving the exhaust port can be turned into turbine power better than the early jet engines managed

the nice man tells us 2025/6 F1 will have maybe 70 kg of fuel
that's 500 hp ICE and 500 hp MGU-K

[Zynerji]

8-10 BAR?!?

You mean PSI?

[Tommy Cookers]

it's 5.5 bar at present

next engine could be small displacement and so more a 'balanced' compound - for higher thermodynamic efficiency
2 stage compressor and perhaps a 2 stage turbine

[Holm86]

it's 5.5 bar at present

next engine could be small displacement and so more a 'balanced' compound - for higher thermodynamic efficiency
2 stage compressor and perhaps a 2 stage turbine

If they're ditching the MGU-H wouldn't it make more sense to up the displacement, and run lower boost, so you don't have such a laggy engine.

[vorticism]

Multi stage...

Series, parallel or sequential?

Axial, yes, but perhaps centrifugal as well ("in line" whatever the nomenclature may be).



How about twin MGUH just to totally miss the point. One MGUH per bank, outboard in the sidepods like 80s F1. MGUK moved inside block vee. 120* bank angle, cylinders halved and offset providing a W12.





As for two strokes, there is the double two stroke option: perhaps a W8 or VR6 set up as a split cycle.

[NL_Fer]

Yet, the sportscar world championship was successfully killed, when an engine that no-one wanted to use was forced.

Bad ideas will have consequences.

I stopped watching WEC when Audi showed up with Diesel engines - Diesel's belong in Semi-trucks, tractors and large commercial vehicles, not in race cars and passenger cars, IMHO. It's not that I dont like the engines, it's the toxic cancer causing by-products they emit that I dislike (plus they are not much fun to drive unless torque is all you care about).

But that is just your opinion. I really like that low rumble, combined with the insane visible acceleration from the onboards. Still at the time we had Porsche V4 and Toyota and LMP2 high rev na engines.

[NL_Fer]

it's 5.5 bar at present

next engine could be small displacement and so more a 'balanced' compound - for higher thermodynamic efficiency
2 stage compressor and perhaps a 2 stage turbine

If they're ditching the MGU-H wouldn't it make more sense to up the displacement, and run lower boost, so you don't have such a laggy engine.

No increase the revs, that is what we all want.

[pgfpro]

it's 5.5 bar at present

next engine could be small displacement and so more a 'balanced' compound - for higher thermodynamic efficiency
2 stage compressor and perhaps a 2 stage turbine

If they're ditching the MGU-H wouldn't it make more sense to up the displacement, and run lower boost, so you don't have such a laggy engine.

After building and racing three different petrol/ethanol 2.0L turbo compound engines you wouldn't need to worry about a laggy turbo engine. In the case of F1 the MGU-H wouldn't even be needed for low rpm spool up. The low-end torque is insane. I have always thought a turbo compound was a perfect fit for F1 clear back in 2013 when a bunch of us were discussion it on this page. Tommy, Gruntguru to name a few.

Both compressors and turbines get to run in their high efficiency's part of the map.
The compressors run cooler due to their high efficiency map so less intercooling needed.
Perfect for lean burn because you can run a much higher boost level utilizing the extra air for the cooling.
Awesome delta-p because the high-pressure turbo can stay in its most efficient part of its turbine map due to the
by-pass gate.

[mzso]

Make the rules. Set them in stone. Open the tender and do NOT believe that it will fail without certain participants.

After that, the racing will sort the rest.

Yet, the sportscar world championship was successfully killed, when an engine that no-one wanted to use was forced.

Bad ideas will have consequences.

Such as "setting rules in stone" that no-one wants to compete by. You can't just ignore what potential competitors want.

[mzso]

Btw. The diesel semitrucks racing on Burningwhee1s are fun as heck to watch as well!

I rather enjoy the 5800lb Tractor pull class - there's just something oddly entertaining watching giant Diesel's driven to destruction!

That said, I'd never go see them in person, I'm not keen on breathing in all those carcinogens!

I can never fathom how people can such ridiculous amounts of time and money to build stuff like these in some parts of the world (sadly not where I live). Don't they need to work?