Concept power units from 2030

[Hoffman900]

it's a fact that fatigue life is driven by stresses proportional to piston acceleration - and so is hugely affected by rpm

race rules often limit rpm but never limit piston speed
the voiture legere & voiturette rules c.1910 first proved that piston acceleration was important and piston speed wasn't

No one said it wasn’t, and history is neat, but the bar is much higher in 2025 than 1910

[gruntguru]

:

piston acceleration

piston acceleration says Indycar would make 13200 rpm if scaled to 53mm stroke
(piston speed says 14500)

Indy is doing it with a heavier piston

NASCAR is seeing near 42m/s peak, with a 400g piston+pin+rings+locks (per rules), spending the majority of their time near there. 3-4 races on each motor, about 2500 miles or so, or about 5-6 F1 race weekends.

A current F1 dimmensions of 53mm stroke, 122mm c-c length, at 15,000 rpm would be 41m/s peak. Piston weight with these PU’s is probably in the 300g-ish range.

If the NASCAR boys can do it with a much heavier piston, the F1 gang can too. To quote my Hendricks contact:

They typically only gain .0-.2 cfm blowby, and are down in power less than most can accurately measure when they are "wore out".

That’s hard data / fact.

There is no correlation between piston speed limitation and piston mass.

Acceleration limit vs mass - maybe.

[Hoffman900]

:

piston acceleration

piston acceleration says Indycar would make 13200 rpm if scaled to 53mm stroke
(piston speed says 14500)

Indy is doing it with a heavier piston

NASCAR is seeing near 42m/s peak, with a 400g piston+pin+rings+locks (per rules), spending the majority of their time near there. 3-4 races on each motor, about 2500 miles or so, or about 5-6 F1 race weekends.

A current F1 dimmensions of 53mm stroke, 122mm c-c length, at 15,000 rpm would be 41m/s peak. Piston weight with these PU’s is probably in the 300g-ish range.

If the NASCAR boys can do it with a much heavier piston, the F1 gang can too. To quote my Hendricks contact:

They typically only gain .0-.2 cfm blowby, and are down in power less than most can accurately measure when they are "wore out".

That’s hard data / fact.

There is no correlation between piston speed limitation and piston mass.

Acceleration limit vs mass - maybe.

It doesn’t take a rocket scientist to see the connection. Honda has two white papers on it and I quote Honda:

Reducing the inertial weight of the recripocating system is the most important subject to increase enginr speeds

And they document how a 16% reduction in piston + pin + ring mass raised rpm by 400rpm for the same longevity. Same piston rod / stroke as before.

For a given bottom and design, a heavier piston is always going to be harder on parts for a given operating duration and going to dictate how long the whole thing can stay together.

[Tommy Cookers]

compared with the F1 cylinder the NASCAR cylinder is about 3x the capacity
wouldn't we expect its piston to be heavier ? (eg about 3x)
it seems to me that NASCAR has the (relatively) 'light' piston

F1 has steel pistons and cannot manage otherwise
it microsecond-manages fuel heat release at 10500-12000 rpm - and IMO can't do this so well at 15000
and is in part compression ignition - this will also not be so good at 15000 ?

[Hoffman900]

compared with the F1 cylinder the NASCAR cylinder is about 3x the capacity
wouldn't we expect its piston to be heavier ? (eg about 3x)
it seems to me that NASCAR has the (relatively) 'light' piston

F1 has steel pistons and cannot manage otherwise
it microsecond-manages fuel heat release at 10500-12000 rpm - and IMO can't do this so well at 15000
and is in part compression ignition - this will also not be so good at 15000 ?

Now we’re discussing combustion concepts. I do agree the HCCI / TJI hybrid may have problems approaching 15,000rpm.

NASCAR pistons can be relatively light since they only see like 110 bar or so peak cylinder pressure. Same as the NA F1 engines.

[gruntguru]

:

Indy is doing it with a heavier piston

NASCAR is seeing near 42m/s peak, with a 400g piston+pin+rings+locks (per rules), spending the majority of their time near there. 3-4 races on each motor, about 2500 miles or so, or about 5-6 F1 race weekends.

A current F1 dimmensions of 53mm stroke, 122mm c-c length, at 15,000 rpm would be 41m/s peak. Piston weight with these PU’s is probably in the 300g-ish range.

If the NASCAR boys can do it with a much heavier piston, the F1 gang can too. To quote my Hendricks contact:

That’s hard data / fact.

There is no correlation between piston speed limitation and piston mass.

Acceleration limit vs mass - maybe.

It doesn’t take a rocket scientist to see the connection. Honda has two white papers on it and I quote Honda:

Reducing the inertial weight of the recripocating system is the most important subject to increase enginr speeds

And they document how a 16% reduction in piston + pin + ring mass raised rpm by 400rpm for the same longevity. Same piston rod / stroke as before.

For a given bottom and design, a heavier piston is always going to be harder on parts for a given operating duration and going to dictate how long the whole thing can stay together.

RPM is not piston speed.
ie Lighter piston > higher rpm limit tells you that the engine was limited by piston acceleration.
F=ma

[Hoffman900]

There is no correlation between piston speed limitation and piston mass.

Acceleration limit vs mass - maybe.

It doesn’t take a rocket scientist to see the connection. Honda has two white papers on it and I quote Honda:

Reducing the inertial weight of the recripocating system is the most important subject to increase enginr speeds

And they document how a 16% reduction in piston + pin + ring mass raised rpm by 400rpm for the same longevity. Same piston rod / stroke as before.

For a given bottom and design, a heavier piston is always going to be harder on parts for a given operating duration and going to dictate how long the whole thing can stay together.

RPM is not piston speed.
ie Lighter piston > higher rpm limit tells you that the engine was limited by piston acceleration.
F=ma

Well there isn’t a lot of velocity if the crank isn’t spinning

There is a reason I included stroke and connecting rod length…

[NL_Fer]

I expect the return of the MGU-H, probably either simplified or specifically cost capped, along with and a pretty big rear-axle MGU-K in the 250-300KW range. I expect a low displacement turbo engine. I can't rule out another 1.6L V6, but I think it might be time to switch engine layouts to an inline 4 or maybe even a tiny 2L V8.

Years back I pitched about a FIA standard GU-H to replace the MGU-H. An exhaust driven turbine generator, charging the ERS with heat energy from the exhaust gas. It would be much more balanced instead of running the MGU-K as a generator during accelerating.

A standard unit would reduce the cost greatly, also because it will less rewarding to develop the combustion side for more MGU-H recovery, like it was with current 1.6 V6 Hybrids in the past.