So this Compression restrictions sounds counter productive. Why are FIA restricting the compression ratio? I presume it has something to do with costs
My guess is that it has something to do with the fuel. Tough to cook up fuel in a lab that has the same energy density / calorific value as fossil fuels which had earth's gravity acting on them for millions of years. Which in turn could mean more turbo compression along with running much richer, with less guarantee against auto-ignition/knock.
So this Compression restrictions sounds counter productive. Why are FIA restricting the compression ratio? I presume it has something to do with costs
My guess is that it has something to do with the fuel. Tough to cook up fuel in a lab that has the same energy density / calorific value as fossil fuels which had earth's gravity acting on them for millions of years. Which in turn could mean more turbo compression along with running much richer, with less guarantee against auto-ignition/knock.
Yeah, that sounds like a good argument for not having a ratio limit. Why have a limit if technically you can't make it work if you excceed the limit?
Re: 2025/2026 Hybrid Powerunit speculation
Posted: 21 Dec 2025, 15:43
by diffuser
Problem I see with this is that Article C.5.4.3 was only updated in October to say that the ratio test would be done at Ambiant temperature. That opened the door for PU manufactures to by pass the 16:1 ratio. Sounds pretty easy to roll it back.
Re: 2025/2026 Hybrid Powerunit speculation
Posted: 21 Dec 2025, 17:43
by vorticism
How about: traverse the entire crankshaft fore or aft slightly along the crank axis, causing all six of the connecting rods big ends to fall away or toward the cylinder centers. +/- Xmm to achieve center when the engine is running to get the extra travel at TDC. Design the crank throw journals and/or bearings with crown such that they are spherical. Might get away with using a typical cylindrical wrist pin and live with the piston itself being angled slightly within the bore during the test. At rest (incl when turned slowly for test), the conrods would be slightly angled, when running the conrods are straight with the big ends aligned with the cylinder centers.
I guess this could be achieved with TE; a static plastic disc pushing on a thrust bearing that contacts the crankshaft f.e. Or by oil pressure or some other means. At operating speeds would centrifugal forces be sufficient to take over and assure alignment? Or would the device always be receiving thrust/axial loads from the conrods trying to push off-axis. In which case how bad would frictional losses to thrust bearings be.
Edit: while this could alter piston stroke sufficiently at rest during a it would require significant displacement of the crankshaft, over 5mm axially to alter the piston TDC locations by ~0.4mm. Conrods would be tilted about 5* off center so spherical journals would be be need on both ends of the conrod which conflicts with the wrist pin needing to be 18-19 mm in diameter i.e. a sphere section fitted to that would be too narrow. It also may conflict with the engine cubic capacity which must be 1600cc +0/-10.
In general it may be good to keep that 10cc tolerance in mind. We have been talking about a 2cc/cylinder alteration of the TDC CC volume, which would be 12cc across 6 cylinders. This has implications for the true amount of compression ratio change available and for what the actual total cubic displacement of the engine would be. I doubt the FIA inspects the cubic capacity of the finished engines but if CAD shows it would be outside of that tolerance window then it would be a non-starter.
------------
Sidenote: the previous 18:1 CR was not inspected for (afaict). This new one will be and there are only so many ways to do that. I’m assuming it is an optical or contact measurement of the piston face performed through the spark plug hole, or with the cylinder heads removed. Obviously running temperatures would not be convenient to achieve in that scenario, short of heating the engine in an oven, removing it, and performing all of the measurements within a certain amount of time as it cools down. Why is a CAD inspection not sufficient? Presumably that is what was done over preceding decade. Why does the FIA now want to measure this instead of infer it?
Re: 2025/2026 Hybrid Powerunit speculation
Posted: 21 Dec 2025, 18:58
by Farnborough
Of interest to the discussion, if not seen before.
How about: traverse the entire crankshaft fore or aft slightly along the crank axis, causing all six of the connecting rods big ends to fall away or toward the cylinder centers. +/- Xmm to achieve center when the engine is running to get the extra travel at TDC. Design the crank throw journals and/or bearings with crown such that they are spherical. Might get away with using a typical cylindrical wrist pin and live with the piston itself being angled slightly within the bore during the test. We're only talking about half millimeters and fractions of degrees here. At rest (incl when turned slowly for test), the conrods are slightly angled, when running the conrods are straight with the big ends aligned with the cylinder centers.
I guess this could be achieved with TE; a static plastic disc pushing on a thrust bearing that contacts the crankshaft f.e. Or by oil pressure or some other means. At operating speeds would centrifugal forces be sufficient to take over and assure alignment? Or would the device always be receiving thrust/axial loads from the conrods trying to push off-axis. In which case how bad would frictional losses to thrust bearings be.
Note the previous 18:1 CR was not inspected for (afaict). This new one will be and there are only so many ways to do that. I’m assuming it is an optical or contact measurement of the piston face performed through the spark plug hole, or with the cylinder heads removed. Obviously running temperatures would not be convenient to achieve in that scenario, short of heating the engine in an oven, removing it, and performing all of the measurements within a certain amount of time as it cools down. Why is a CAD inspection not sufficient? Presumably that is what was done over preceding decade. Why does the FIA now want to measure this instead of infer it?
Angled pistons are a neat receipt for a fast piston and cylinder failure, it's why is important for the rods to not being twisted nor bent.
Nevertheless, I can understand why you talk about spherical throws (and piston pin!) to angle the rod, but I still cannot figure how you get the throw from offset to centered.
Interesting. Most interesting is they have in cylinder pressure sensors.....
Timestamp? I ask because the new regs seem to imply such sensors may not always be in place. My post on the previous page regarding dismountable components.
Interesting. Most interesting is they have in cylinder pressure sensors.....
Timestamp? I ask because the new regs seem to imply such sensors may not always be in place. My post on the previous page regarding dismountable components.
I'd have to go back and watch it but it was the 2nd question in Q&A section at the end.
I thought it was interesting cause I figured they can use that for compression ratio testing?
Interesting. Most interesting is they have in cylinder pressure sensors.....
Timestamp? I ask because the new regs seem to imply such sensors may not always be in place. My post on the previous page regarding dismountable components.
Around 37mins 20 secs. He later says they may get rid of them for the 2026 regulations on cost grounds as the sensors are expensive.
Re: 2025/2026 Hybrid Powerunit speculation
Posted: 23 Dec 2025, 23:09
by vorticism
Is 16:1 less about limiting compression and more about limiting IVO:EVO duration ratios (i.e. turbocharger contribution)? If they were using Miller cycle previously then 18:1 may also have been about that. Since the IVO duration would have been somewhat free if Miller cycle was the norm. I suppose the dev path otherwise would have been ever longer IVO durations along with higher boost pressures but not necessarily higher in-cylinder compression.
Interesting. Most interesting is they have in cylinder pressure sensors.....
Timestamp? I ask because the new regs seem to imply such sensors may not always be in place. My post on the previous page regarding dismountable components.
Around 37mins 20 secs. He later says they may get rid of them for the 2026 regulations on cost grounds as the sensors are expensive.
Thanks for that. The 'dismountable components' list for the combustion chamber includes a 'component' to replace a pressure sensor, but not a pressure sensor itself. Maybe they're used for breaking in the engine, then plugged for use in competition. Reinserted for diagnostics between FP, Q, & races.
The plug is of free geometry (beyond diameter) & material (afaict) so could be another magic TE device to guess at. A plunger filled with wax or plastic and voila, TE based CR effector. Seems a bit too on the nose, though. FIA: "What is that?"
It's silicon-carbon, not carbide. They've been talking about silicon this and that in the anode for many years. It never really came to pass. Best I remember is Tesla adding some silicon.
In any way a proper solid-state battery is better. It has neither silicon nor carbon, just lithium metal.
It's silicon-carbon, not carbide. They've been talking about silicon this and that in the anode for many years. It never really came to pass. Best I remember is Tesla adding some silicon.
In any way a proper solid-state battery is better. It has neither silicon nor carbon, just lithium metal.
Are SSB's anywhere near advanced enough to be considered for use in F1? I believe Mercedes, who are the only relevant manu here that has also conducted real life prototyping and testing, say they are at least still 4 years away, from producing EVs using SSB'S. I believe it was developed in-house, in conjunction with HPP.
It's silicon-carbon, not carbide. They've been talking about silicon this and that in the anode for many years. It never really came to pass. Best I remember is Tesla adding some silicon.
In any way a proper solid-state battery is better. It has neither silicon nor carbon, just lithium metal.
Are SSB's anywhere near advanced enough to be considered for use in F1? I believe Mercedes, who are the only relevant manu here that has also conducted real life prototyping and testing, say they are at least still 4 years away, from producing EVs using SSB'S. I believe it was developed in-house, in conjunction with HPP.
I initially misunderstood the requirements. The battery duty cycle in Formula 1 is fundamentally different from that of an EV. An F1 battery may alternate between charge and discharge on the order of 50 times per lap, which demands extremely high C-rates and rapid transient response. I don’t recall the exact regulation, but F1 is limited to roughly three energy storage systems per season.
This is in stark contrast to EV batteries, which typically experience a few charge cycles per week, followed by relatively slow, continuous discharge. EV battery design prioritizes long-term degradation resistance and calendar life, often with warranties extending to around 200,000 km.