F1 2026 compression ratio controversy

[Klutch9]

It’s been in the news that Mercedes and RBPT (Red Bull/Ford) have found a way to dynamically increase the compression ratio of their engines when hot. Per the regulations, they cannot use a mechanism like the Infiniti VC engines do, where the stroke is modified.

So how on earth are they doing it?

It’s been genuinely bugging me and I’m fascinated by it. My only guess is that they have found a material for the connecting rod that expands when hot. True, this would raise the height of BDC, thereby reducing compression volume, but it would also slightly raise TDC and the piston’s proximity to the head, which would, as a ratio, given how close the piston would already be to the head at ambient, increase compression.

The rulebook does limit what materials can be used for certain components, so I don’t know if they even have any freedom with the conrod materials. But it’s the only way I can think of. The valves, head, and cylinder walls are more or less fixed, otherwise you would have clearance issues if they changed dimension. Maybe the piston crown has some weird expanding material?

 

[Chris142]

Sounds like something smokey yunik would do.

 

[Klutch9]

Sounds like something smokey yunik would do.

Haha true. It’s about time F1 had a ‘controversy’ like this though. Rule books are meant to be exploited in racing. They always have been. This is akin to the double-diffuser of 09. Love to see teams innovate outside the box.

 

[Chris142]

Do they measure the compression by measurements like combustion chamber size or cranking pressure?

 

[Klutch9]

Do they measure the compression by measurements like combustion chamber size or cranking pressure?

Not sure. All I know is that for the 2026 regs, there is a specific note that mentions the compression ratio is measured at ‘ambient temperature’, whatever that means. That note was not present in the previous rulebook, likely why it is being exploited now.

 

[Chris142]

Not sure. All I know is that for the 2026 regs, there is a specific note that mentions the compression ratio is measured at ‘ambient temperature’, whatever that means. That note was not present in the previous rulebook, likely why it is being exploited now.

That sounds like they are measuring the psi and not the chamber volume. If so maybe they came up with a ring material that "Bleeds off" compression until it gets up to temperature?

A lot of cam overlap will also lower cylinder pressure at low speeds.

 

[Klutch9]

That sounds like they are measuring the psi and not the chamber volume. If so maybe they came up with a ring material that "Bleeds off" compression until it gets up to temperature?

A lot of cam overlap will also lower cylinder pressure at low speeds.

You may be right on both of those points. It’s fascinating either way. That’s why I love this stuff. It’s like redneck engineering with money behind it.

 

[Hall]

Go to YouTube - there are videos explaining what is most likely going on (as no one can say with 100% certainty). I want to say it involves the 'height' is where they're gaining.

 

[barryh]

I haven't looked a youtube but a proper explanation for this doesn't seem to exist in the F1 media. It has to be more subtle than a change in the static compression ratio because that's not the whole story in terms of fine comparisons between one engine and another. Real or dynamic compression doesn't begin until the inlet valves are closed which is way past the bottom dead centre point where static compression is measured. Throw in the fact that these are turbo engines and it gets even more complicated. It will be fascinating when it does get explained.

 

[Vercingetorix]

Or it could be rumours fueled to force other teams to spend money on dead end research. I see none of this amounting to anything concrete.

 

[Hall]

Or it could be rumours fueled to force other teams to spend money on dead end research. I see none of this amounting to anything concrete.

Speculation is Mercedes discovered (or developed) it a couple years ago and in the meantime, RBPT hired many powertrain engineers away from Mercedes, who brought the concept with them. Hence why Mercedes and RBPT are the only engine makers believed to use this. My question is, how does anyone outside of either team know this exists ?