How F1 teams are using 3D printed pistons to circumvent compression rules
Additive manufacturing has enabled targeted thermal expansion to boost effective compression beyond the 16:1 limit set for the 2026 season, and is understandably ruffling feathers in the paddock
Formula 1’s governing body, the FIA, introduced a revised compression ratio ceiling of 16:1 for the 2026 season, down from the previous limit of 18:1, with the aim of reducing engine development costs and lowering barriers for new entrants. But as has been the case many times before in a sport where the world’s top engineers are employed, a smart loophole is being exploited to squeeze the absolute maximum out of the cars, and this time it involves 3D printing.
The FIA measures the static geometric piston compression ratio with the engine at ambient temperature, calculating the difference between cylinder volume at bottom dead center and top dead center. That measurement methodology left an opening.
At racing speeds and temperatures, pistons expand and connecting rods stretch, altering the effective compression ratio beyond what the static test captures. Mercedes and Red Bull have been reported in F1 media as two teams that have identified this gap, and set about engineering pistons specifically designed to exploit it.
Additive manufacturing as a performance tool
F1 teams have shifted in recent years from forging pistons from steel billet — a subtractive process — to 3D printing them. The additive process allows engineers to design complex internal structures within solid metal components and vary material density throughout each part.
Engineers at both Mercedes and Red Bull appear to have used that capability to create internal piston architectures that channel combustion heat toward specific points, causing the piston to expand more than a conventionally manufactured equivalent would. The result, if effective, is a compression ratio at operating temperature that exceeds the 16:1 figure recorded during the FIA’s static test.
Rivals seek regulatory clarification and the FIA are on it
Other teams reportedly submitted a joint letter to the FIA requesting clarification on the engine regulations and asking that a measurement methodology be established to assess compression ratios at operating temperature.
The FIA has reacted, and a rule change that will measure compression ratio at both ambient and a “representative operating temperature of 130ºC” has been proposed, due to come into effect at the start of August.
That will be just over the halfway point in the season, meaning there’s still a lot of racing under the current grey-area rule to be run this year. As it stands, Mercedes has won the opening two Grands Prix of 2026.
They normally forget pistons from steel billets? Steel? That’s some heavy pistons!!!
If the measurement were taken at ambient temperature, then thermal n physical expansion will be the same for all of the competitors Therefore. No Problem!
All the engine builders can do as their sneaky engineers will be able to get away with. Surely there’s a limited possibility for “stretching” the rules as presented but I wonder if it would amount to . . . let’s say 1.5 points on compression.
If the engines have to be “baked” to a temperature higher than ambient, imagine the extra complexity it will add to scrutineering. Would the whole car have to be baked? Or just the engine? Not the sort of thing can easily be done at the track.
All Hail to Smokey’s dictum (if it don’t say no, then it’s ok)
Jess
I highly doubt F1 is doing billet steel pistons, an aluminum alloy is much more likely.
I think that was implied. Like they were forging them from steel, now they are 3D printing them (in other materials). And yes I’m pretty sure they use aluminum from Elementum 3D. We did an article about it in the past
Or possibly Scalmalloy from APWORKS