16:1 to 18:1

[BassVirolla]

I'm not going to participate in the wankfest, but a while back there was some research that indicated that high CRs weren't especially efficient, above 20:1 the theoretical thermodynamic advantages were outweighed by mechanical inefficiencies.

Totally true. In the speculation thread I exposed some reasons to not being pushing CR nor boost more than strictly necessary.

[Gooch]

When the initial rumor is this light on information I have a hard time putting any stock in it. Similar to the skid block situation this year, all we’ve been given is a mechanical property with zero explanation or even a hint of the mechanism that’s taking would be needed to take advantage of it. The regulations are too tightly defined to make it as simple as material selection…

Also, FWIW the 2026 regulations state you must use a “conventional” valve seats and guides. I don’t think deep cylindrical valves would use conventional seats, aside from the fact that you would have to compromise so many other aspects of the design to make them work.

[BassVirolla]

When the initial rumor is this light on information I have a hard time putting any stock in it. Similar to the skid block situation this year, all we’ve been given is a mechanical property with zero explanation or even a hint of the mechanism that’s taking would be needed to take advantage of it. The regulations are too tightly defined to make it as simple as material selection…

Also, FWIW the 2026 regulations state you must use a “conventional” valve seats and guides. I don’t think deep cylindrical valves would use conventional seats, aside from the fact that you would have to compromise so many other aspects of the design to make them work.

Not deep I was thinking. A standard poppet valve with 2 or 3 mm of cylindrical section above the conical seat can be fitted with very much standard guides and seats, but compromising flow (not as important in boosted vs. atmospheric, but important, nevertheless).

[Dr. Acula]

Perhaps the 18:1 Cr that was permitted in the past was close to optimal and there was little gain in exceeding it. Now they have to reduce the CR two points from the 18:1 they have been working with for a number of seasons.

That is my thought also, but mind that we had also the MGU-H past seasons and regularized fuel. Maybe the fuel could not handle more compression as there is the limited factor.

Actually if i'm not mistaken, the 2026 rules also introduce a maximum reasearch octane number for the fuel of 102. Until now there was no maximum octane number stated in the rules. So if they can run 18:1 with 102 octane, fuel certainly wasn't the limiting factor before. For instance in Germany you can even buy 102RON fuel at some fuel stations.

[Rodak]

I'm not going to participate in the wankfest, but a while back there was some research that indicated that high CRs weren't especially efficient, above 20:1 the theoretical thermodynamic advantages were outweighed by mechanical inefficiencies.

And the compression ratio is simply the geometric ratio of volume at the top and bottom of the stroke; there is also an increase in actual compression ration from the turbo-charged inlet air. I'd be curious to know the operating compression ratio; seems at 18:1 geometric we are in the area of compression ignition and knock. The 2026 fuel is limited to a RON of 102.0; that hardly seems usable in a turbo-charged 18:1 engine, so they must have some tricks to achieve a higher actual octane rating higher than the RON number.

[Tommy Cookers]

And the compression ratio is simply the geometric ratio of volume at the top and bottom of the stroke; there is also an increase in actual compression ration from the turbo-charged inlet air. I'd be curious to know the operating compression ratio; seems at 18:1 geometric we are in the area of compression ignition and knock. The 2026 fuel is limited to a RON of 102.0; that hardly seems usable in a turbo-charged 18:1 engine, so they must have some tricks to achieve a higher actual octane rating higher than the RON number.

'operating' CR is like ON - a mythical concept
quantifying detonation resistance isn't like eg measuring temperature - there's no 'detonation thermometer'

ON is reference fuel behaviour at 600 or 900 rpm in a design of test engine fixed for almost a century
not how a different fuel behaves at 10500 rpm in a different engine
100 MON and 100 RON are of course identical with reference fuel but with street fuel very different
this proves that ON is a very poor predictor for high-speed engines
in 1960 Honda dominated motorcycle GPs with 18000 rpm engines winning on 75 ON fuel - because it was fast-igniting

hybrid F1 cools the air after compression then chills it (by Miller-style expansion) then ....
compresses in-cylinder equivalent to 8:1 then fuels & burns at dilution ratio 1.3 lambda and expands equivalent to 16:1
high pressure but not very high temperature
(pre-2026) Honda even tuned-out its VLIM at times to cool the charge enough to avoid detonation

F1 racing went 'pump petrol' in 1958 - but different countries had different 'pump petrol' ....
so they settled on Avgas the global standard (parrots say 100/130 but 108/135 was in F1 fuel blends pre 58)
Avgas 100/130 means 100 ON when NA lean and 30% more power (ie 130) when supercharged rich
there's no such thing as 130 ON - no matter if it is so-called for practical reasons (130 is a PN performance number)
Avgas 100/130 will actually be about 106 ON /130 PN because US crude lacks aromatics so needs 106 ON to get 130 PN
Avgas 108/135 PN was quite handy (its actual ON might have been c. 112)

in WW2 there was a mini war US vs UK involving US breaches of fuel specs contracted (the UK and its 100/130 won)
100/130 was a UK invention rather difficult to make from US crude (except Californian)
essentially its high aromatic content helps supercharging when used rich (but ON test's reference fuels don't)

[BassVirolla]

hybrid F1 cools the air after compression then chills it (by Miller-style expansion) then ....
compresses it in-cylinder eg '9:1 CR' then fuels & burns at dilution ratio eg 1.3 lambda and expands at '16:1 ER'
very high pressure but not very high temperature
(pre-2026) Honda even tuned-out its VLIM at times to cool the charge enough to avoid detonation
don't worry !

Never is enough stressed that power are harvested from raw heat energy during expansion. Compression is a by-product of the need to expand.

[maddim]

When the initial rumor is this light on information I have a hard time putting any stock in it. Similar to the skid block situation this year, all we’ve been given is a mechanical property with zero explanation or even a hint of the mechanism that’s taking would be needed to take advantage of it. The regulations are too tightly defined to make it as simple as material selection…

Also, FWIW the 2026 regulations state you must use a “conventional” valve seats and guides. I don’t think deep cylindrical valves would use conventional seats, aside from the fact that you would have to compromise so many other aspects of the design to make them work.

Too many unknowns for so complex accusation. I do think we may never know the full contrast of the situation here. As It may go to a settlement by the FIA if there is ground.

[FW17]

The engine regulations do not mention anything on the type on injectors that an be used.

The manufacturer can therefore use an compressed air assisted injector that could inject more air into the cylinder as it reaches TDC to increase the compressed air pressure from 77bar to 87bar by adding 2cc of compressed air.

[wuzak]

C5.1.9 Dismountable components assembled to the Cylinder Head exposed to the combustion chamber must be approved by the FIA Technical Department and are confined to:
a. The Fuel Injectors
b. The spark plugs
c. The poppet valves (Article C5.3.4)
d. A single component per cylinder to replace an In-Cylinder pressure sensor with a maximum outside diameter of 7mm.
e. A component whose part residing in the cylinder head is wholly contained in a cylinder of external diameter 15 mm coaxial with the axis of the spark plug

[BassVirolla]

The engine regulations do not mention anything on the type on injectors that an be used.

The manufacturer can therefore use an compressed air assisted injector that could inject more air into the cylinder as it reaches TDC to increase the compressed air pressure from 77bar to 87bar by adding 2cc of compressed air.

There are rules about the ingressing and exhaust of air / gasses (all air entering the cylinder must pass through...). I don't remember the exact wording, but it would be worth a search through the new ruleset. I don't think this that you expose is allowed.

[vorticism]

Might be possible to incorporate it into the fuel injector assembly or spark plug along with the defense of them not being fully defined, although trying to add after IVC will demand a second higher pressure air compressor, but the big rule against it is C5.3.1 "Pressure charging may only be affected by use of a sole single stage, single side turbocharger compressor with a..."

[FW17]

The primary purpose of air injection is fuel atomization, the injector regulations is not very elaborate on limits of type of injector that may be used.

Yes a compressor would be required, likely cam driven.

[wuzak]

The engine regulations do not mention anything on the type on injectors that an be used.

The manufacturer can therefore use an compressed air assisted injector that could inject more air into the cylinder as it reaches TDC to increase the compressed air pressure from 77bar to 87bar by adding 2cc of compressed air.

There are rules about the ingressing and exhaust of air / gasses (all air entering the cylinder must pass through...). I don't remember the exact wording, but it would be worth a search through the new ruleset. I don't think this that you expose is allowed.

C5.6 Engine intake air
C5.6.1 With the exception of incidental leakage through joints or cooling ducts in the engine intake air system (either into or out of the system), all air entering the engine must enter the bodywork through a maximum of two inlets which are located on a single X plane between XC= −850 and XR= −500 and above Z=200.
Furthermore, any such inlets must be visible in their entirety when viewed from the front of the car without the driver seated in the car and with the secondary roll structure and any parts attached to it removed (see Article C12.4.2).
C5.6.2 The addition of any substance other than fuel, as described in Article C5.11.3, into the air destined for combustion is forbidden. Exhaust gas recirculation is forbidden.
C5.6.3 There must be no more than one butterfly or rotating barrel, as explained in the Throttle definition, in the geometrical path of air exiting the Compressor Outlet and going to any cylinder.
C5.6.4 Any component of the ICE intake air system forming a volume whose surface area, measured perpendicular to the geometrical path of the air directed to any cylinder, is at least 10000mm² per bank or 3400mm² per cylinder supplied, shall be defined as Engine Plenum.

[gruntguru]

The engine regulations do not mention anything on the type on injectors that an be used.

The manufacturer can therefore use a compressed air assisted injector that could inject more air into the cylinder as it reaches TDC to increase the compressed air pressure from 77bar to 87bar by adding 2cc of compressed air.

Two posts above yours, it was stressed that high "compression" is not the goal. (The goal is high "expansion"). The current engines deliberately reduce the "compression" using Miller cycle valve timing. The 18:1 permitted CR is utilised in order to achieve a high expansion ratio.