Honda Power Unit Hardware & Software

[Craigy]

Where did he say that? Give us the quote and source.

It doesn't make sense to "thump your chest" about something when you are actually struggling with it. He's a real paddock source saying the exact opposite of what you are saying That doesn't eliminate the possibility that someone is struggling with their fuel, but not everyone.

Maybe problems is not the right word but technically challenges are the are his real words "They are more complex, because they are composed of elements with different evaporation points.”
“With sustainable fuels, some components evaporate later than others, and this makes combustion more complex. We are working with hotter combustion chambers, a condition that opens up.

In other words he didn't say what you attributed to him. But he very clearly said that they could do higher compression, and that the 16:1 CR was "too low".

On the topic of compression ratios for the 2026 formula.

The measured value at room temperature of 16:1 or just under that value, for legality. The Historic limit of 18:1 at any time. If I read this correctly, there's not really a hot running limit at all in 2026. You could engineer for 20:1 or more in a hot running config if you wanted to.

People keep talking about this as if the manufacturers have achieved the hot running/room temperature differences using only the bottom end (crank/rods/pistons) - presumably some form of elastic behaviour based on temperature. I think it'd make a lot of sense for it to also be in the injector, where you could (for example) control temperature of materials at will more easily.

A system to up the compression ratio by (for example) disabling a cooling loop that causes a material to expand and lower the volume in the injectors would be pretty straightforward to implement and relatively easy to tune.

With 70kg per race and 3000MJ/h flow, 2026 is a fuel efficiency formula for the ICE. Nobody's measuring the horrific NOx emissions practically guaranteed from high compression ratios, so the development direction is pretty clear in that regard.

If nothing else, ignore the discussed 18:1 limit. It was in the previous formula and doesn't exist any more. The sky is the limit now.

[Badger]

Maybe problems is not the right word but technically challenges are the are his real words "They are more complex, because they are composed of elements with different evaporation points.”
“With sustainable fuels, some components evaporate later than others, and this makes combustion more complex. We are working with hotter combustion chambers, a condition that opens up.

In other words he didn't say what you attributed to him. But he very clearly said that they could do higher compression, and that the 16:1 CR was "too low".

On the topic of compression ratios for the 2026 formula.

The measured value at room temperature of 16:1 or just under that value, for legality. The Historic limit of 18:1 at any time. If I read this correctly, there's not really a hot running limit at all in 2026. You could engineer for 20:1 or more in a hot running config if you wanted to.

People keep talking about this as if the manufacturers have achieved the hot running/room temperature differences using only the bottom end (crank/rods/pistons) - presumably some form of elastic behaviour based on temperature. I think it'd make a lot of sense for it to also be in the injector, where you could (for example) control temperature of materials at will more easily.

A system to up the compression ratio by (for example) disabling a cooling loop that causes a material to expand and lower the volume in the injectors would be pretty straightforward to implement and relatively easy to tune.

With 70kg per race and 3000MJ/h flow, 2026 is a fuel efficiency formula for the ICE. Nobody's measuring the horrific NOx emissions practically guaranteed from high compression ratios, so the development direction is pretty clear in that regard.

If nothing else, ignore the discussed 18:1 limit. It was in the previous formula and doesn't exist any more. The sky is the limit now.

There was never a "hot limit" as far as I understand, the test was always done at ambient. However there are several regulatory constraints on materials and such that make it hard to greatly expand your compression ratio much above the ambient measurement.

[Craigy]

In other words he didn't say what you attributed to him. But he very clearly said that they could do higher compression, and that the 16:1 CR was "too low".

On the topic of compression ratios for the 2026 formula.

The measured value at room temperature of 16:1 or just under that value, for legality. The Historic limit of 18:1 at any time. If I read this correctly, there's not really a hot running limit at all in 2026. You could engineer for 20:1 or more in a hot running config if you wanted to.

People keep talking about this as if the manufacturers have achieved the hot running/room temperature differences using only the bottom end (crank/rods/pistons) - presumably some form of elastic behaviour based on temperature. I think it'd make a lot of sense for it to also be in the injector, where you could (for example) control temperature of materials at will more easily.

A system to up the compression ratio by (for example) disabling a cooling loop that causes a material to expand and lower the volume in the injectors would be pretty straightforward to implement and relatively easy to tune.

With 70kg per race and 3000MJ/h flow, 2026 is a fuel efficiency formula for the ICE. Nobody's measuring the horrific NOx emissions practically guaranteed from high compression ratios, so the development direction is pretty clear in that regard.

If nothing else, ignore the discussed 18:1 limit. It was in the previous formula and doesn't exist any more. The sky is the limit now.

There was never a "hot limit" as far as I understand, the test was always done at ambient. However there are several regulatory constraints on materials and such that make it hard to greatly expand your compression ratio much above the ambient measurement.

I understand why you say this - it's not in the clear, direct wording of the old reg, but in the effect of it.
Previous reg -- https://www.fia.com/sites/default/files ... -04-07.pdf

5.4.6 No cylinder of the engine may have a geometric compression ratio higher than 18.0.

Note that this never specified how it was measured, which is why it was taken to be universally applied, even when hot. Presumably the FIA just looked at stuff along the lines of in-cylinder pressure transducers from team telemetry.
The new regs aren't worded like that at all.

2026 wording (so different that it's essentially a different regulation)

C5.4.3 No cylinder of the engine may have a geometric compression ratio higher than 16.0. The procedure
to measure this value will be detailed by each PU Manufacturer according to the Guidance
Document FIA-F1-DOC-C042 and executed at ambient temperature. This procedure must be
approved by the FIA Technical Department and included in the PU Manufacturer homologation
dossier.

https://www.fia.com/system/files/docume ... 2-10_0.pdf

Hm. Perhaps this belongs in a different thread rather than the Honda dedicated one.

[Badger]

On the topic of compression ratios for the 2026 formula.

The measured value at room temperature of 16:1 or just under that value, for legality. The Historic limit of 18:1 at any time. If I read this correctly, there's not really a hot running limit at all in 2026. You could engineer for 20:1 or more in a hot running config if you wanted to.

People keep talking about this as if the manufacturers have achieved the hot running/room temperature differences using only the bottom end (crank/rods/pistons) - presumably some form of elastic behaviour based on temperature. I think it'd make a lot of sense for it to also be in the injector, where you could (for example) control temperature of materials at will more easily.

A system to up the compression ratio by (for example) disabling a cooling loop that causes a material to expand and lower the volume in the injectors would be pretty straightforward to implement and relatively easy to tune.

With 70kg per race and 3000MJ/h flow, 2026 is a fuel efficiency formula for the ICE. Nobody's measuring the horrific NOx emissions practically guaranteed from high compression ratios, so the development direction is pretty clear in that regard.

If nothing else, ignore the discussed 18:1 limit. It was in the previous formula and doesn't exist any more. The sky is the limit now.

There was never a "hot limit" as far as I understand, the test was always done at ambient. However there are several regulatory constraints on materials and such that make it hard to greatly expand your compression ratio much above the ambient measurement.

I understand why you say this - it's not in the clear, direct wording of the old reg, but in the effect of it.
Previous reg -- https://www.fia.com/sites/default/files ... -04-07.pdf

5.4.6 No cylinder of the engine may have a geometric compression ratio higher than 18.0.

Note that this never specified how it was measured, which is why it was taken to be universally applied, even when hot. Presumably the FIA just looked at stuff along the lines of in-cylinder pressure transducers from team telemetry.
The new regs aren't worded like that at all.

2026 wording (so different that it's essentially a different regulation)

C5.4.3 No cylinder of the engine may have a geometric compression ratio higher than 16.0. The procedure
to measure this value will be detailed by each PU Manufacturer according to the Guidance
Document FIA-F1-DOC-C042 and executed at ambient temperature. This procedure must be
approved by the FIA Technical Department and included in the PU Manufacturer homologation
dossier.

https://www.fia.com/system/files/docume ... 2-10_0.pdf

Hm. Perhaps this belongs in a different thread rather than the Honda dedicated one.

The test hasn't changed, it was always done at ambient. The FIA only clarified this in the written rules recently though, presumably because some manufacturers were starting to ask questions about this "trick". But the FIA have never had a way of measuring hot compression. The way I understand it is that it was never an issue when the rule said 18:1 because that was so close to the optimum CR that there was little to no gain to be had by trying to push it much more. When they lowered it to 16:1 it suddenly became an area for improvement.